UNITED STATES


SECURITIES AND EXCHANGE COMMISSION


Washington, D.C. 20549





FORM 10-Q/A


(Amendment No. 1)





(Mark One)


ý  QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934


For the quarterly period ended June 30, 2014


OR


o  TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 (d) OF THE SECURITIES EXCHANGE ACT OF 1934


For the transition period from                      to


Commission File Number: 001-36065





ACCELERON PHARMA INC.


(Exact name of registrant as specified in its charter)


Delaware(State or other jurisdiction ofincorporation or organization)2836(Primary Standard IndustrialClassification Code Number)27-0072226(I.R.S. EmployerIdentification Number)


128 Sidney Street


Cambridge, MA 02139


(617) 649-9200


(Address, including zip code, and telephone number, including


area code, of registrant’s principal executive offices)





Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes  x No  o





Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). Yes  ý No  o





Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer”, “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):


Large accelerated fileroAccelerated fileroNon-accelerated filerx(Do not check if a smaller reporting company)Smaller reporting companyo





Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes  o No  ý





As of July 31, 2014 , there were 31,797,085 shares of the registrant’s Common Stock, par value $0.001 per share, outstanding.




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EXPLANATORY NOTE





This Amendment No. 1 to the Quarterly Report on Form 10-Q/A (this “Amendment”) amends the Quarterly Report on Form 10-Q for the quarter ended June 30, 2014 (the “Original Report”) filed by Acceleron Pharma Inc. with the Securities and Exchange Commission on August 12, 2014. This Amendment is being filed solely for the purpose of amending an error on Exhibit 32.1 under Item 6 of Part II of the Original Report.





Except as described above, no other changes have been made to the Original Report and this Amendment does not modify or update disclosures in the Original Report and does not reflect subsequent events occurring after date of the Original Report. Accordingly, this Amendment should be read in conjunction with the Original Report, which continues to speak as of the date of the Original Report.





PART II.  OTHER INFORMATION





Item 6. Exhibits





(a) Exhibits





ExhibitnumberDescription of exhibit31.1Certification of Principal Executive Officer pursuant to Rule 13a-14(a) or Rule 15d-14(a) of the Securities Exchange Act of 1934, as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.31.2Certification of Principal Financial Officer pursuant to Rule 13a-14(a) or Rule 15d-14(a) of the Securities Exchange Act of 1934, as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.32.1Certification of Principal Executive Officer and Principal Financial Officer pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002.











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Signatures





Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.





ACCELERON PHARMA INC.Date: August 12, 2014By:/s/ JOHN L. KNOPF, PH.D.John L. Knopf, Ph.D.Chief Executive Officer and PresidentDate: August 12, 2014By:/s/ KEVIN F. MCLAUGHLINKevin F. McLaughlinChief Financial Officer


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ExhibitnumberDescription of exhibit31.1Certification of Principal Executive Officer pursuant to Rule 13a-14(a) or Rule 15d-14(a) of the Securities Exchange Act of 1934, as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.31.2Certification of Principal Financial Officer pursuant to Rule 13a-14(a) or Rule 15d-14(a) of the Securities Exchange Act of 1934, as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.32.1Certification of Principal Executive Officer and Principal Financial Officer pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002.








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