Lysosomal exocytosis by macrophages as a druggable mechanism for anti-inflammatory clearance of dead adipocytes in adipose tissue

The clearance of dead adipocytes in adipose tissue (AT) poses a major challenge due to their large size, which exceeds the phagocytic capacity of macrophages and prevents classical, anti-inflammatory efferocytosis. Instead, adipose tissue macrophages (ATMs) accumulate around dying adipocytes, forming crown-like structures (CLS), and engage in lysosomal exocytosis - the extracellular degradation of adipocytes. In this study, we used an ex vivo explant model of murine epididymal white AT, cultured over seven days to investigate pharmacological strategies that modulate lysosomal exocytosis. We observed a progressive increase in CLS formation, secretion of the lysosomal enzymes ß-Hexosaminidase A (HEXA) and lysosomal acid lipase (LAL), and surface abundance of LAMP1 and LAMP2, confirming ATMs as key mediators of this process. Notably, activation of lysosomal exocytosis with the mTOR inhibitor Rapamycin enhanced adipocyte clearance and significantly reduced inflammatory ATM abundance and TNF-α secretion. Bulk RNA sequencing of ATMs revealed a highly significant impact of Rapamyin on ATM proliferation. In contrast, inhibition of lysosomal exocytosis with PIKfyve inhibitor Apilimod or targeted inhibition of LAL using Lalistat-2 disrupted lysosomal function and promoted a pro-inflammatory ATM phenotype. Our findings highlight lysosomal exocytosis as a critical pathway for the resolution of dead adipocytes and the regulation of inflammation in adipose tissue. Pharmacological enhancement of this process may represent a promising therapeutic approach to attenuate inflammation in AT and its metabolic consequences, including insulin resistance and type 2 diabetes.