Exhibit 3.2

AMENDED AND RESTATED BYLAWS

Acceleron Pharma Inc.

Article I - STOCKHOLDERS

Section 1.

Annual Meeting.

An annual meeting of the stockholders, for the election of directors to succeed those whose terms expire and for the transaction of such other business as may properly come before the meeting, shall be held at such place, on such date, and at such time as the Board of Directors (the “Board of Directors”) of Acceleron Pharma Inc. (the “Corporation”) shall each year fix, which date shall be within 13 months of the last annual meeting of stockholders or, if no such meeting has been held, the date of incorporation.

Section 2.

Special Meetings.

Special meetings of the stockholders, for any purpose or purposes prescribed in the notice of the meeting, may be called by the Board of Directors or the president and shall be held at such place, on such date, and at such time as they or he or she shall fix.

Section 3.

Notice of Meetings.

Notice of the place, if any, date, and time of all meetings of the stockholders, the means of remote communications, if any, by which stockholders and proxyholders may be deemed to be present in person and vote at such meeting, and the record date for determining the stockholders entitled to vote at the meeting, if such date is different from the record date for determining stockholders entitled to notice of the meeting, shall be given, not less than 10 nor more than 60 days before the date on which the meeting is to be held, to each stockholder entitled to vote at such meeting as of the record date for determining the stockholders entitled to notice of the meeting, except as otherwise provided herein or required by law (meaning, here and hereinafter, as required from time to time by the Delaware General Corporation Law or the Certificate of Incorporation of the Corporation (the “Certificate of Incorporation”)).

When a meeting is adjourned to another time or place, notice need not be given of the adjourned meeting if the time and place, if any, thereof, and the means of remote communications, if any, by which stockholders and proxyholders may be deemed to be present in person and vote at such adjourned meeting are announced at the meeting at which the adjournment is taken; provided, however, that if the date of any adjourned meeting is more than 30 days after the date for which the meeting was originally noticed, notice of the place, if any, date, and time of the adjourned meeting and the means of remote communications, if any, by which stockholders and proxyholders may be deemed to be present in person and vote at such adjourned meeting, shall be given to each stockholder in conformity herewith. If after the adjournment a new record date for stockholders entitled to vote is fixed for the adjourned meeting, the Board of Directors shall fix a new record date for notice of such adjourned meeting, which record date shall not precede the date upon which the resolution fixing the record date is adopted by the Board of Directors and, except as otherwise required by law, shall not be more than 60 nor less than 10 days before the date of such adjourned meeting, and shall give notice of the adjourned meeting to each stockholder of record entitled to vote at such adjourned meeting as of the record date fixed for notice of such adjourned meeting. At any adjourned meeting, any business may be transacted which might have been transacted at the original meeting.

Section 4.

Quorum.

At any meeting of the stockholders, the holders of a majority of all of the shares of the stock entitled to vote at the meeting, present in person or by proxy, shall constitute a quorum for all purposes, unless or except to the extent that the presence of a larger number may be required by law. Where a separate vote by a class or classes or series is required, a majority of the shares of such class or classes or series present in person or represented by proxy shall constitute a quorum entitled to take action with respect to that vote on that matter. A quorum once established, shall not be broken by the subsequent withdrawal of enough votes to leave less than a quorum.

If a quorum shall fail to attend any meeting, the chairman of the meeting or the holders of a majority of the shares of stock entitled to vote who are present, in person or by proxy, may adjourn the meeting to another place, if any, date, or time. At any such adjourned meeting at which there is a quorum, any business may be transacted that might have been transacted at the meeting originally called.

Section 5.

Organization.

Such person as the Board of Directors may have designated or, in the absence of such a person, the President of the Corporation or, in his or her absence, such person as may be chosen by the holders of a majority of the shares entitled to vote who are present, in person or by proxy, shall call to order any meeting of the stockholders and act as chairman of the meeting. In the absence of the Secretary of the Corporation, the secretary of the meeting shall be such person as the chairman of the meeting appoints.

Section 6.

Conduct of Business.

The chairman of any meeting of stockholders shall determine the order of business and the procedure at the meeting, including such regulation of the manner of voting and the conduct of discussion as seem to him or her in order. The date and time of the opening and closing of the polls for each matter upon which the stockholders will vote at the meeting shall be announced at the meeting.

Section 7.

Proxies and Voting.

At any meeting of the stockholders, every stockholder entitled to vote may vote in person or by proxy authorized by an instrument in writing or by a transmission permitted by law filed in accordance with the procedure established for the meeting. Any copy, facsimile, email or other reliable reproduction of the writing or transmission created pursuant to this paragraph may be substituted or used in lieu of the original writing or transmission for any and all purposes for which the original writing or transmission could be used, provided that such copy, facsimile, email or other reproduction shall be a complete reproduction of the entire original writing or transmission.

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The Corporation may, and to the extent required by law, shall, in advance of any meeting of stockholders, appoint one or more inspectors to act at the meeting and make a written report thereof. The Corporation may designate one or more alternate inspectors to replace any inspector who fails to act. If no inspector or alternate is able to act at a meeting of stockholders, the person presiding at the meeting may, and to the extent required by law, shall, appoint one or more inspectors to act at the meeting. Each inspector, before entering upon the discharge of his or her duties, shall take and sign an oath faithfully to execute the duties of inspector with strict impartiality and according to the best of his or her ability. Every vote taken by ballots shall be counted by an inspector or inspectors appointed by the chairman of the meeting.

All elections shall be determined by a plurality of the votes cast, and except as otherwise required by law, all other matters shall be determined by a majority of the votes cast affirmatively or negatively.

Section 8.

Stock List.

The officer who has charge of the stock ledger of the Corporation shall, at least 10 days before every meeting of stockholders, prepare and make a complete list of stockholders entitled to vote at any meeting of stockholders, provided, however, if the record date for determining the stockholders entitled to vote is less than 10 days before the meeting date, the list shall reflect the stockholders entitled to vote as of the 10th day before the meeting date, arranged in alphabetical order and showing the address of each such stockholder and the number of shares registered in his or her name. Such list shall be open to the examination of any stockholder for a period of at least 10 days prior to the meeting in the manner provided by law.

A stock list shall also be open to the examination of any stockholder during the whole time of the meeting as provided by law. This list shall presumptively determine (a) the identity of the stockholders entitled to examine such stock list and to vote at the meeting and (b) the number of shares held by each of them.

Section 9.

Consent of Stockholders in Lieu of Meeting.

Any action required to be taken at any annual or special meeting of stockholders of the Corporation, or any action which may be taken at any annual or special meeting of the stockholders, may be taken without a meeting, without prior notice and without a vote, if a consent or consents in writing, setting forth the action so taken, shall be signed by the holders of outstanding stock having not less than the minimum number of votes that would be necessary to authorize or take such action at a meeting at which all shares entitled to vote thereon were present and voted and shall be delivered to the Corporation by delivery to its registered office in Delaware, its principal place of business, or an officer or agent of the Corporation having custody of the book in which proceedings of meetings of stockholders are recorded. Delivery made to the Corporation’s registered office shall be made by hand or by certified or registered mail, return receipt requested.

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Every written consent shall bear the date of signature of each stockholder who signs the consent and no written consent shall be effective to take the corporate action referred to therein unless, within 60 days of the earliest dated consent delivered to the Corporation, a written consent or consents signed by a sufficient number of holders to take action are delivered to the Corporation in the manner prescribed in the first paragraph of this Section. A telegram, cablegram or other electronic transmission consenting to an action to be taken and transmitted by a stockholder or proxyholder, or by a person or persons authorized to act for a stockholder or proxyholder, shall be deemed to be written, signed and dated for the purposes of this Section to the extent permitted by law. Any such consent shall be delivered in accordance with Section 228(d)(1) of the Delaware General Corporation Law.

Any copy, facsimile, email or other reliable reproduction of a consent in writing may be substituted or used in lieu of the original writing for any and all purposes for which the original writing could be used, provided that such copy, facsimile, email or other reproduction shall be a complete reproduction of the entire original writing.

Article II - BOARD OF DIRECTORS

Section 1.

General Powers.

The business and affairs of the Corporation shall be managed by or under the direction of the Board of Directors. The Board of Directors may adopt such rules and procedures, not inconsistent with the Certificate of Incorporation, these Bylaws, or applicable law, as it may deem proper for the conduct of its meetings and the management of the Corporation.

Section 2.

Number and Term of Office.

The number of directors who shall constitute the whole Board of Directors shall be such number as the Board of Directors shall from time to time have designated, provided that the size of the initial Board of Directors shall be equal to the number of directors elected by the Incorporator of the Corporation. Each director shall be elected for a term of the earlier of one year and until his or her successor is elected and qualified, except as otherwise provided herein or required by law.

Whenever the authorized number of directors is increased between annual meetings of the stockholders, a majority of the directors then in office shall have the power to elect such new directors for the balance of a term and until their successors are elected and qualified. Any decrease in the authorized number of directors shall not become effective until the expiration of the term of the directors then in office unless, at the time of such decrease, there shall be vacancies on the board which are being eliminated by the decrease.

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Section 3.

Vacancies.

If the office of any director becomes vacant by reason of death, resignation, disqualification, removal or other cause, a majority of the directors remaining in office, although less than a quorum, may elect a successor for the unexpired term and until his or her successor is elected and qualified.

Section 4.

Regular Meetings.

Regular meetings of the Board of Directors shall be held at such place or places, on such date or dates, and at such time or times as shall have been established by the Board of Directors and publicized among all directors. A notice of each regular meeting shall not be required.

Section 5.

Special Meetings.

Special meetings of the Board of Directors may be called by one-third of the directors then in office (rounded up to the nearest whole number) or by the President and shall be held at such place, on such date, and at such time as they or he or she shall fix. Notice of the place, date, and time of each such special meeting shall be given to each director by whom it is not waived by mailing written notice not less than five days before the meeting or by facsimile, email or other electronic transmission of the same not less than 24 hours before the meeting. Unless otherwise indicated in the notice thereof, any and all business may be transacted at a special meeting.

Section 6.

Quorum.

At any meeting of the Board of Directors, a majority of the total number of the whole Board of Directors shall constitute a quorum for all purposes. If a quorum shall fail to attend any meeting, a majority of those present may adjourn the meeting to another place, date, or time, without further notice or waiver thereof.

Section 7.

Participation in Meetings By Conference Telephone.

Members of the Board of Directors, or of any committee thereof, may participate in a meeting of such Board of Directors or committee by means of conference telephone or other communications equipment by means of which all persons participating in the meeting can hear each other and such participation shall constitute presence in person at such meeting.

Section 8.

Conduct of Business.

At any meeting of the Board of Directors, business shall be transacted in such order and manner as the Board of Directors may from time to time determine, and all matters shall be determined by the vote of a majority of the directors present, except as otherwise provided herein or required by law. Action may be taken by the Board of Directors without a meeting if all members thereof consent thereto in writing or by electronic transmission, and the writing or writings or electronic transmission or transmissions are filed with the minutes of proceedings of the Board of Directors. Such filing shall be in paper form if the minutes are maintained in paper form and shall be in electronic form if the minutes are maintained in electronic form.

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Section 9.

Compensation of Directors.

Directors, as such, may receive, pursuant to resolution of the Board of Directors, fixed fees and other compensation for their services as directors, including, without limitation, their services as members of committees of the Board of Directors.

Section 10.

Action Without Meeting.

Unless otherwise restricted by the Certificate of Incorporation or these Bylaws, any action required or permitted to be taken at any meeting of the Board of Directors or of any committee thereof may be taken without a meeting if all directors or members of such committee, as the case may be, consent thereto in writing or by electronic transmission, and the writings or electronic transmissions are filed with the minutes of proceedings of the Board of Directors or committee in accordance with applicable law.

Section 11.

Resignation.

Any director may resign at any time by notice given in writing or by electronic transmission to the Corporation. Such resignation shall take effect at the date of receipt of such notice by the Corporation or at such later time as is therein specified. A verbal resignation shall not be deemed effective until confirmed by the director in writing or by electronic transmission to the Corporation.

Section 12.

Removal.

Except as prohibited by applicable law or the Certificate of Incorporation, the stockholders entitled to vote in an election of directors may remove any director from office at any time, with or without cause, by the affirmative vote of a majority in voting power thereof.

Article III - COMMITTEES

Section 1.

Committees of the Board of Directors.

The Board of Directors may from time to time designate committees of the Board of Directors, with such lawfully delegable powers and duties as it thereby confers, to serve at the pleasure of the Board of Directors and shall, for those committees and any others provided for herein, elect a director or directors to serve as the member or members, designating, if it desires, other directors as alternate members who may replace any absent or disqualified member at any meeting of the committee. In the absence or disqualification of any member of any committee and any alternate member in his or her place, the member or members of the committee present at the meeting and not disqualified from voting, whether or not he or she or they constitute a quorum, may by unanimous vote appoint another member of the Board of Directors to act at the meeting in the place of the absent or disqualified member.

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Section 2.

Conduct of Business.

Each committee may determine the procedural rules for meeting and conducting its business and shall act in accordance therewith, except as otherwise provided herein or required by law. Adequate provision shall be made for notice to members of all meetings; one-third of the members shall constitute a quorum unless the committee shall consist of one or two members, in which event one member shall constitute a quorum; and all matters shall be determined by a majority vote of the members present. Action may be taken by any committee without a meeting if all members thereof consent thereto in writing or by electronic transmission, and the writing or writings or electronic transmission or transmissions are filed with the minutes of the proceedings of such committee. Such filing shall be in paper form if the minutes are maintained in paper form and shall be in electronic form if the minutes are maintained in electronic form.

Article IV - OFFICERS

Section 1.

Generally.

The officers of the Corporation shall be elected annually by the Board of Directors and shall include a president, a treasurer, one or more vice presidents, and a secretary. The Board of Directors, in its discretion, may also elect one or more vice presidents, assistant treasurers, assistant secretaries, and other officers. Any two or more offices may be held by the same person. Each officer shall hold office until his or her successor is elected and qualified or until his or her earlier resignation or removal.

Section 2.

President.

The president shall have general supervision over the business of the Corporation and other duties incident to the office of president, and any other duties as may be from time to time assigned to the president by the Board of Directors and subject to the control of the Board of Directors in each case. He or she shall have power to sign all stock certificates, contracts and other instruments of the Corporation which are authorized and shall have general supervision and direction of all of the other officers, employees and agents of the Corporation.

Section 3.

Vice President.

Each vice president shall have such powers and duties as may be delegated to him or her by the Board of Directors or the president. One vice president shall be designated by the Board of Directors to perform the duties and exercise the powers of the President in the event of the President’s absence or disability.

Section 4.

Treasurer.

The Treasurer shall have the responsibility for maintaining the financial records of the Corporation. He or she shall make such disbursements of the funds of the Corporation as are authorized and shall render from time to time an account of all such transactions and of the financial condition of the Corporation. The Treasurer shall also perform such other duties as the Board of Directors may from time to time prescribe.

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Section 5.

Secretary.

The Secretary shall issue all authorized notices for, and shall keep minutes of, all meetings of the stockholders and the Board of Directors. He or she shall have charge of the corporate books and shall perform such other duties as the Board of Directors may from time to time prescribe.

Section 6.

Delegation of Authority.

In case any officer is absent, or for any other reason that the Board of Directors may deem sufficient, the president or the Board of Directors may delegate for the time being the powers or duties of such officer to any other officer or to any director.

Section 7.

Removal.

Any officer of the Corporation may be removed at any time, with or without cause, by the Board of Directors.

Section 8.

Action with Respect to Securities of Other Corporations.

Unless otherwise directed by the Board of Directors, the President or any officer of the Corporation authorized by the President shall have power to vote and otherwise act on behalf of the Corporation, in person or by proxy, at any meeting of stockholders of or with respect to any action of stockholders of any other corporation in which this Corporation may hold securities and otherwise to exercise any and all rights and powers which this Corporation may possess by reason of its ownership of securities in such other corporation.

Article V - STOCK

Section 1.

Certificates of Stock.

Shares of stock of the Corporation may, but need not be, represented by certificates. Each holder of stock represented by certificates shall be entitled to a certificate signed by, or in the name of the Corporation by, any two authorized officers of the Corporation, including the President or a Vice President, and by the Secretary or an Assistant Secretary, or the Treasurer or an Assistant Treasurer, certifying the number of shares owned by him or her. Any or all of the signatures on the certificate may be by facsimile.

Section 2.

Transfers of Stock.

Transfers of stock shall be made only upon the transfer books of the Corporation kept at an office of the Corporation or by transfer agents designated to transfer shares of the stock of the Corporation. Except where a certificate is issued in accordance with Section 4 of Article V of these Bylaws, an outstanding certificate, if one has been issued, for the number of shares involved shall be surrendered for cancellation before a new certificate, if any, is issued therefor.

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Section 3.

Record Date.

In order that the Corporation may determine the stockholders entitled to notice of any meeting of stockholders or any adjournment thereof, the Board of Directors may, except as otherwise required by law, fix a record date, which record date shall not precede the date upon which the resolution fixing the record date is adopted by the Board of Directors, and which record date shall not be more than 60 nor less than 10 days before the date of such meeting. If the Board of Directors so fixes a date, such date shall also be the record date for determining the stockholders entitled to vote at such meeting unless the Board of Directors determines, at the time it fixes such record date, that a later date on or before the date of the meeting shall be the date for making such determination. If no record date is fixed by the Board of Directors, the record date for determining stockholders entitled to notice of and to vote at a meeting of stockholders shall be at the close of business on the day next preceding the day on which notice is given or, if notice is waived, at the close of business on the day next preceding the day on which the meeting is held. A determination of stockholders of record entitled to notice of or to vote at a meeting of stockholders shall apply to any adjournment of the meeting; provided, however, that the Board of Directors may fix a new record date for determination of stockholders entitled to vote at the adjourned meeting, and in such case shall also fix as the record date for stockholders entitled to notice of such adjourned meeting the same or an earlier date as that fixed for determination of stockholders entitled to vote in accordance with the foregoing provisions of this Section 3 at the adjourned meeting.

In order that the Corporation may determine the stockholders entitled to receive payment of any dividend or other distribution or allotment of any rights or the stockholders entitled to exercise any rights in respect of any change, conversion or exchange of stock, or for the purpose of any other lawful action, the Board of Directors may fix a record date, which record date shall not precede the date upon which the resolution fixing the record date is adopted, and which record date shall be not more than 60 days prior to such action. If no record date is fixed, the record date for determining stockholders for any such purpose shall be at the close of business on the day on which the Board of Directors adopts the resolution relating thereto.

In order that the Corporation may determine the stockholders entitled to consent to corporate action without a meeting, (including electronic transmission as permitted by law), the Board of Directors may fix a record date, which shall not precede the date upon which the resolution fixing the record date is adopted by the Board of Directors, and which record date shall be not more than ten days after the date upon which the resolution fixing the record date is adopted. If no record date has been fixed by the Board of Directors and no prior action by the Board of Directors is required by the Delaware General Corporation Law, the record date shall be the first date on which a consent setting forth the action taken or proposed to be taken is delivered to the Corporation in the manner prescribed by Article I, Section 9 hereof. If no record date has been fixed by the Board of Directors and prior action by the Board of Directors is required by the Delaware General Corporation Law with respect to the proposed action by consent of the stockholders without a meeting, the record date for determining stockholders entitled to consent to corporate action without a meeting shall be at the close of business on the day on which the Board of Directors adopts the resolution taking such prior action.

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Section 4.

Lost, Stolen or Destroyed Certificates.

In the event of the loss, theft or destruction of any certificate of stock, another may be issued in its place pursuant to such regulations as the Board of Directors may establish concerning proof of such loss, theft or destruction and concerning the giving of a satisfactory bond or bonds of indemnity.

Section 5.

Regulations.

The issue, transfer, conversion and registration of certificates of stock shall be governed by such other regulations as the Board of Directors may establish.

Article VI - NOTICES

Section 1.

Notices.

If mailed, notice to stockholders shall be deemed given when deposited in the mail, postage prepaid, directed to the stockholder at such stockholder’s address as it appears on the records of the Corporation. Without limiting the manner by which notice otherwise may be given effectively to stockholders, any notice to stockholders may be given by electronic transmission in the manner provided in Section 232 of the Delaware General Corporation Law.

Section 2.

Waivers.

A written waiver of any notice, signed by a stockholder or director, or waiver by electronic transmission by such person, whether given before or after the time of the event for which notice is to be given, shall be deemed equivalent to the notice required to be given to such person. Neither the business nor the purpose of any meeting need be specified in such a waiver.

Article VII - MISCELLANEOUS

Section 1.

Facsimile Signatures.

In addition to the provisions for use of facsimile signatures elsewhere specifically authorized in these Bylaws, facsimile signatures of any officer or officers of the Corporation may be used whenever and as authorized by the Board of Directors or a committee thereof.

Section 2.

Books and Records.

Any records administered by or on behalf of the Corporation in the regular course of its business, including its stock ledger, books of account, and minute books, may be maintained on any information storage device, method, or one or more electronic networks or databases (including one or more distributed electronic networks or databases); provided that the records so kept can be converted into clearly legible paper form within a reasonable time, and, with respect to the stock ledger, the records so kept comply with Section 224 of the Delaware General Corporation Law. The Corporation shall so convert any records so kept upon the request of any person entitled to inspect such records pursuant to applicable law.

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Section 3.

Corporate Seal.

The Board of Directors may provide a suitable seal, containing the name of the Corporation, which seal shall be in the charge of the Secretary. If and when so directed by the Board of Directors or a committee thereof, duplicates of the seal may be kept and used by the Treasurer or by an Assistant Secretary or Assistant Treasurer.

Section 4.

Reliance upon Books, Reports and Records.

Each director, each member of any committee designated by the Board of Directors, and each officer of the Corporation shall, in the performance of his or her duties, be fully protected in relying in good faith upon the books of account or other records of the Corporation and upon such information, opinions, reports or statements presented to the Corporation by any of its officers or employees, or committees of the Board of Directors so designated, or by any other person as to matters which such director or committee member reasonably believes are within such other person’s professional or expert competence and who has been selected with reasonable care by or on behalf of the Corporation.

Section 5.

Fiscal Year.

The fiscal year of the Corporation shall begin on January 1 and end on December 31 of each year.

Section 6.

Checks, Notes, Drafts, Etc.

All checks, notes, drafts, or other orders for the payment of money of the Corporation shall be signed, endorsed, or accepted in the name of the Corporation by such officer, officers, person, or persons as from time to time may be designated by the Board of Directors or by an officer or officers authorized by the Board of Directors to make such designation.

Section 7.

Dividends.

Subject to applicable law and the Certificate of Incorporation, dividends upon the shares of capital stock of the Corporation may be declared by the Board of Directors at any regular or special meeting of the Board of Directors. Dividends may be paid in cash, in property, or in shares of the Corporation's capital stock, unless otherwise provided by applicable law or the Certificate of Incorporation

Section 8.

Time Periods.

In applying any provision of these Bylaws which requires that an act be done or not be done a specified number of days prior to an event or that an act be done during a period of a specified number of days prior to an event, calendar days shall be used, the day of the doing of the act shall be excluded, and the day of the event shall be included.

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Section 9.

Conflict with Applicable Law or Certificate of Incorporation.

These Bylaws are adopted subject to any applicable law and the Certificate of Incorporation. Whenever these Bylaws may conflict with any applicable law or the Certificate of Incorporation, such conflict shall be resolved in favor of such law or the Certificate of Incorporation

Article VIII - INDEMNIFICATION OF DIRECTORS AND OFFICERS

Section 1.

Right to Indemnification.

The Corporation shall indemnify, defend and hold harmless, to the fullest extent permitted by applicable law as it presently exists or may hereafter be amended, any person (an “Indemnitee”) who was or is made, or is threatened to be made, a party or is otherwise involved in any action, suit or proceeding, whether civil, criminal, administrative or investigative (a “Proceeding”), by reason of the fact that he or she, or a person for whom he or she is the legal representative, is or was a director or an officer of the Corporation or, while a director or an officer of the Corporation, is or was serving at the request of the Corporation as a director, officer, employee, member, trustee or agent of another corporation or of a partnership, joint venture, trust, nonprofit entity or other enterprise (including, but not limited to, service with respect to employee benefit plans) (any such entity, an “Other Entity”), against all liability and loss suffered (including, but not limited to, expenses (including, but not limited to, attorneys’ fees and expenses), judgments, fines and amounts paid in settlement actually and reasonably incurred by such Indemnitee in connection with such Proceeding). Notwithstanding the preceding sentence, the Corporation shall be required to indemnify an Indemnitee in connection with a Proceeding (or part thereof) commenced by such Indemnitee only if the commencement of such Proceeding (or part thereof) by the Indemnitee was authorized by the Board of Directors of the Corporation or the Proceeding (or part thereof) relates to the enforcement of the Corporation’s obligations under this Section 1 of ARTICLE VIII.

Section 2.

Right to Advancement of Expenses.

The Corporation shall to the fullest extent not prohibited by applicable law pay, on an as-incurred basis, all expenses (including, but not limited to attorneys’ fees and expenses) incurred by an Indemnitee in defending any proceeding in advance of its final disposition. Such advancement shall be unconditional, unsecured and interest free and shall be made without regard to Indemnitee’s ability to repay any expenses advanced; provided, however, that, to the extent required by law, such payment of expenses in advance of the final disposition of the Proceeding shall be made only upon receipt of an unsecured undertaking by the Indemnitee to repay all amounts advanced if it should be ultimately determined that the Indemnitee is not entitled to be indemnified under this ARTICLE VIII or otherwise.

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Section 3.

Claims.

If a claim for indemnification (following the final disposition of such proceeding) or advancement of expenses under this ARTICLE VIII is not paid in full within 60 days after a written claim therefor by the Indemnitee has been received by the Corporation, the Indemnitee may file suit to recover the unpaid amount of such claim and, if successful in whole or in part, shall be entitled to be paid the expense of prosecuting such claim to the fullest extent permitted by law. In any such action the Corporation shall have the burden of proving that the Indemnitee is not entitled to the requested indemnification or advancement of expenses under applicable law.

Section 4.

Insurance.

The Corporation shall have the power to purchase and maintain insurance on behalf of any person who is or was a director, officer, trustee, employee, member, trustee or agent of the Corporation, or was serving at the request of the Corporation as a director, officer, trustee, employee or agent of an Other Entity, against any liability asserted against the person and incurred by the person in any such capacity, or arising out of his or her status as such, whether or not the Corporation would have the power or the obligation to indemnify such person against such liability under the provisions of this ARTICLE VIII or the Delaware General Corporation Law.

Section 5.

Non-Exclusivity of Rights.

The rights conferred on any Indemnitee by this ARTICLE VIII are not exclusive of other rights arising under any bylaw, agreement, vote of directors or stockholders or otherwise, and shall inure to the benefit of the heirs and legal representatives of such Indemnitee.

Section 6.

Amounts Received from an Other Entity.

Subject to Section 7 of ARTICLE VIII, the Corporation’s obligation, if any, to indemnify or to advance expenses to any Indemnitee who was or is serving at the Corporation’s request as a director, officer, employee or agent of an Other Entity shall be reduced by any amount such Indemnitee may collect as indemnification or advancement of expenses from such Other Entity.

Section 7

Amendment or Repeal.

Any right to indemnification or to advancement of expenses of any Indemnitee arising hereunder shall not be eliminated or impaired by an amendment to or repeal of this ARTICLE VIII after the occurrence of the act or omission that is the subject of the civil, criminal, administrative or investigative action, suit, proceeding or other matter for which indemnification or advancement of expenses is sought.

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Section 8

Other Indemnification and Advancement of Expenses.

This ARTICLE VIII shall not limit the right of the Corporation, to the extent and in the manner permitted by law, to indemnify and to advance expenses to persons other than Indemnitees when and as authorized by appropriate corporate action.

Section 9

Reliance.

Indemnitees who after the date of the adoption of this ARTICLE VIII become or remain an Indemnitee described in Section 1 of ARTICLE VIII will be conclusively presumed to have relied on the rights to indemnity, advancement of expenses and other rights contained in this ARTICLE VIII in entering into or continuing the service. The rights to indemnification and to the advancement of expenses conferred in this ARTICLE VIII will apply to claims made against any Indemnitee described in Section 1 of Article VIII arising out of acts or omissions that occurred or occur either before or after the adoption of this ARTICLE VIII in respect of service as a director or officer of the corporation or other service described in Section 1 of ARTICLE VIII.

Section 10

Successful Defense.

In the event that any proceeding to which an Indemnitee is a party is resolved in any manner other than by adverse judgment against the Indemnitee (including, without limitation, settlement of such proceeding with or without payment of money or other consideration) it shall be presumed that the Indemnitee has been successful on the merits or otherwise in such proceeding for purposes of Section 145(c) of the Delaware General Corporation Law. Anyone seeking to overcome this presumption shall have the burden of proof and the burden of persuasion by clear and convincing evidence.

Article IX - AMENDMENTS

These Bylaws may be adopted, amended or repealed by the Board of Directors at any meeting or by the stockholders at any meeting. In the case of any such amendment or repeal of Article VIII or any section thereof, the amendment or repeal shall be subject to Article VIII, Section 7.

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ACCELERON PHARMA INC 8-K