HSPA12A impairs lipophagy to exaggerate septic cardiomyopathy by promoting MTOR's competition against LC3-II in binding with PNPLA2

Accumulation of lipid droplets (LDs) in cardiomyocytes contributes to developmentof septic cardiomyopathy, a fatal complication of critical illness in patients.Lipophagy is a selective autophagic mechanism for LD degradation. This processis inhibited by mTOR, but is activated by PNPLA2 via its binding with LC3-II toform LD-containing autophagosomes. However, optimum lipophagic interventions tomanage septic cardiomyopathy have not been developed, thus furtherinvestigation is required to identify novel regulators of lipophagy in theseptic heart. HSPA12A (heat shockprotein 12A) encodes an atypical member of the HSPA/HSP70family. Here, we report that sepsis decreased HSPA12Aexpression in cardiomyocytes, whereas cardiomyocyte-specific HSPA12Aoverexpression aggravated sepsis-induced cardiomyocyte death and cardiacdysfunction in mice. Notably, HSPA12A promoted sepsis-induced LD accumulationin cardiomyocytes. By contrast, HSPA12A inhibited lipophagy in septiccardiomyocytes, as reflected by a decreased level of LD-containing autophagosomes,a reduced content of LC3-II, and an increased level of SQSTM1/p62. In-depthmolecular analysis revealed that HSPA12A increased phosphorylation of mTOR andthus its binding to PNPLA2 on LDs. mTOR thereby competed against LC3-II inbinding with PNPLA2 to suppress LD-containing autophagosome formation subsequentlyimpairing lipophagy and ultimately promoting cardiomyocyte death to exaggerate septiccardiomyopathy. We demonstrated that mTOR competed against LC3-II in bindingwith PNPLA2 to inhibit lipophagy and also identified HSPA12A as a driver ofthis competition with mTOR to impair lipophagy for exaggerating septic cardiomyopathy. Strategiesthat inhibit HSPA12A in cardiomyocytes might be a potential therapeuticintervention for septic cardiomyopathy.

Cardiomyocyte; HSPA12A; MTOR; PNPLA2; lipophagy; septic cardiomyopathy.