X0306 4 2018-03-06 0 0001280600 ACCELERON PHARMA INC XLRN 0001126490 POPS RICHARD F 128 SIDNEY STREET CAMBRIDGE MA 02139 1 0 0 0 Common Stock 2018-03-06 4 M 0 37500 5.08 A 68750 D Common Stock 2018-03-06 4 S 0 34598 41.34 D 34152 D Common Stock 2018-03-06 4 S 0 2902 42.32 D 31250 D Option to Purchase Common Stock 5.08 2018-03-06 4 M 0 37500 0 D 2018-03-27 Common Stock 37500 0 D The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $40.98 to $41.97 inclusive. The reporting person undertakes to provide Acceleron Pharma Inc., any security holder of Acceleron Pharma Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote (1) to this Form 4. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $41.98 to $42.70 inclusive. The reporting person undertakes to provide Acceleron Pharma Inc., any security holder of Acceleron Pharma Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote (2) to this Form 4. The options of registrants common stock vested as to one third of the shares annually beginning on the first anniversary of the grant. /s/ John D. Quisel, as attorney-in-fact for Richard F. Pops 2018-03-08