X0306 4 2020-05-22 0 0001383701 Histogen Inc. HSTO 0001324466 Mento Steven J C/O HISTOGEN INC. 10655 SORRENTO VALLEY ROAD, SUITE 200 SAN DIEGO CA 92121 1 0 0 0 Common Stock 2020-05-22 4 M 0 65000 0.00 A 71000 D Common Stock 2020-05-22 4 F 0 31428 0.56 D 39572 D Common Stock 42708 I See footnote Restricted Stock Units 2020-05-22 4 M 0 65000 0.00 D Common Stock 65000 0 D Held by a family trust of which Dr. Mento is a trustee. Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock. Pursuant to the Agreement and Plan of Merger and Reorganization (the "Merger Agreement") by and among Conatus Pharmaceuticals Inc. ("Conatus"), Chinook Merger Sub, Inc. and Histogen Inc., all outstanding Conatus restricted stock units vested in full and were settled in shares of common stock prior to the closing of the merger contemplated by the Merger Agreement. All share amounts in this Form 4 reflect the 10 for 1 reverse stock split implemented by Conatus Pharmaceuticals Inc. on May 26, 2020 in connection with the Merger Agreement. /s/ Steven J. Mento 2020-05-27