Deficiency of heat shock protein A12A promotes browning of white adipose tissues in mice

Browning of white adipose tissues (WAT) is critical for a variety of physiological and pathophysiological events. Given the limited understanding in molecular control of WAT browning, further research is needed. Heat shock protein AI2A (HSPAI2A) is a new member of multigene Hsp70 family. This study investigated the effect of HSPAI2A on the browning of WAT. WAT Browning in mice was induced by cold exposure for 5 days. We observed that nuclear HSPAI2A content was increased in WAT after cold exposure, while deficiency of HSPA12A (Hspal 2a-1-) promoted the cold-induced browning of WAT in mice compared to wild type (WT) littermates. Accordingly, Hspal2a-/- mice showed attenuation of body temperature drop and increase of thermogenic gene expression compared to WT mice after cold exposure. However, in vitro experiments demonstrated that HSPA12A deficiency in primary white adipocytes did not affect their browning and thermogenic gene expression. Further loss- and gain-of-HSPAI2A functional studies revealed that HSPA12A deficiency promoted whereas HSPA12A overexpression impeded M2 macrophage polarization. Importantly, the conditioned medium (CM) from Hspal2a-/- bone marrow-derived macrophages (BMDMs) enhanced the browning of primary white adipocytes when compared to the CM from WT BMDMs. The data identified macrophage HSPA12A as a novel regulator of WAT browning through a paracrine mechanism. Targeting HSPA12A might provide meaningful advances for the management of browning-associated physiological events such as hypothermia adaptation and pathophysiological disorders such as obesity and cancer-related cachexia.