CHIT1 and metabolic disease: The first two AM-like macrophage populations—referred to here as mac_ MRC1+FABP4hiCHIT1+(mac_1) and mac_MRC1hiFABP4hiCHIT1+(mac_2)—highly expressed MRC1, Fatty Acid-Binding Protein 4 (FABP4), which is primarily involved in lipid metabolism and has implications for metabolic diseases and inflammation, and Chitotriosidase 1 (CHIT1), which is associated with the immune response and known as a marker for macrophage activation (Fig. 2B), suggesting their contribution to metabolism and immune response.