Lipotoxic stress, a hallmark of metabolic dysfunction-associated fatty liver disease (MAFLD), disrupts cellular homeostasis by shifting the balance between autophagy and apoptosis. While autophagy generally promotes cell survival, its impairment coupled with enhanced apoptosis contributes to liver injury. However, The molecular mechanisms governing this transition remain unclear.
p21 (CDKN1A), a cyclin-dependent kinase inhibitor, and TXNIP (thioredoxin-interacting protein), a regulator of cellular redox and glucose metabolism, have both been implicated in MAFLD pathogenesis. p21 regulates cell-cycle arrest and stress-induced cell fate decisions, while TXNIP promotes oxidative stress by inhibiting thioredoxin and modulating AMPK–mTOR signaling. Both proteins influence autophagy, yet their potential interplay in hepatocytes has not been explored.
To begin with, analysis of the obesity-related single-cell RNA-seq dataset GSE136103 showed that both TXNIP and p21 are commonly expressed in hepatocytes, implicating their potential interplay in the liver under metabolic stress. Building on this finding, we performed a series of cellular experiments using HepG2 cells to investigate whether TXNIP and p21 act cooperatively or antagonistically in the regulation of autophagy and apoptosis. We found that overexpression of either p21 or TXNIP individually enhanced autophagy, but co-expression of TXNIP with p21 suppressed autophagy and instead promoted apoptosis. Mechanistically, TXNIP directly bound to p21 in both endogenous and exogenous settings, and this interaction was further strengthened under lipotoxic stress. Moreover, palmitic acid elevated the expression of both TXNIP and p21, thereby regulating the balance between autophagy and apoptosis.
These results identify TXNIP as a key molecular switch that reprograms p21 function from an autophagy-promoting to an apoptosis-inducing role under metabolic stress.