miR-378a and NPNT coordinate autophagy regulation in podocytes through mTOR and MAPK signaling

Abstract

Autophagy is a critical homeostatic mechanism in podocytes, maintaining cellular integrity under stress and proteostatic challenges. Dysregulation of autophagy has been implicated in different glomerular diseases such as diabetes and membranous glomerulonephropathy (MGN), yet the underlying molecular drivers remain incompletely understood. We identified microRNA-378a (miR-378a), previously found upregulated in MGN, as a functional enhancer of autophagic flux in human podocytes and tubular epithelial cells. While miR-378a did not directly alter transcription of canonical autophagy genes (ATG2A, ATG5, ATG7, ATG12), it increased autophagic flux through suppression of mTOR phosphorylation at Ser2448. Given that NPNT is a miR-378a target and a key glomerular basement membrane component, we investigated its role in autophagy regulation. NPNT knockdown reduced ATG2A, ATG7, and BCN1 expression, but paradoxically increased autophagic flux, independent of mTOR, accompanied by enhanced ERK1/2 phosphorylation. These findings reveal a dual-layered regulatory network in which miR-378a promotes autophagy via mTOR inhibition, whereas NPNT modulates autophagy probably through MAPK-dependent signaling. Our results highlight the complex interplay between miRs, extracellular matrix components, and intracellular signaling pathways in podocyte autophagy. Dysregulation of these pathways in kidney disease may reflect both adaptive and maladaptive responses, providing mechanistic insights and potential therapeutic targets to preserve glomerular filtration barrier integrity in immune-mediated kidney disease.