Astragaloside IV Restores Autophagy and Inhibits Apoptosis for Podocyte Protection in Diabetic Nephropathy by Inhibiting Notch1 Signaling via SIRT6-Mediated Deacetylation.

Abstract

Astragaloside IV (AS-IV) has demonstrated efficacy in ameliorating proteinuria and attenuating renal tubular damage in preclinical diabetic nephropathy (DN) models. Despite these multi-target benefits, the molecular mechanisms underlying its podocyte-protective effects remain largely uncharacterized, particularly its potential epigenetic regulatory capacity within glomerular cells. This study aimed to test the hypothesis that AS-IV protects against DN by activating the deacetylase sirtuin 6 (SIRT6). Specifically, AS-IV activates SIRT6, which deacetylates Histone H3 at Lysine 9 (H3K9) at the Notch1 promoter, thereby suppressing Notch1 expression. This suppression is expected to enhance autophagy and reduce apoptosis, ultimately repairing renal filtration barrier injury. A murine model of DN was induced with streptozotocin and a high-fat diet. To simulate diabetic damage, MPC-5 podocytes were subjected to high glucose (HG, 33 mM). Renal function metrics were extensively evaluated, and glomerular histopathological and ultrastructural changes were assessed by hematoxylin and eosin staining and electron microscopy. Subsequently, downstream mechanisms involving podocyte autophagy and apoptosis were investigated by immunofluorescence staining and Western blotting. To confirm that SIRT6 directly regulates Notch1 transcription via histone deacetylation, our study utilized chromatin immunoprecipitation (ChIP). Our results showed that AS-IV treatment alleviated renal biochemical and pathological abnormalities in DN mice and attenuated podocyte injury, evidenced by restoring nephrin and podocin expression and reducing glomerular basement membrane thickness (p < 0.01). Functionally, AS-IV treatment reversed HG-induced podocyte apoptosis and autophagy dysfunction (p < 0.01). Mechanistically, AS-IV was confirmed to directly bind to SIRT6 (Kd = 0.164 μM). ChIP assays demonstrated increased SIRT6 occupancy and consequently reduced H3K9ac enrichment at the Notch1 promoter (p < 0.01). In summary, AS-IV may ameliorate DN by activating the SIRT6/H3K9ac/Notch1 epigenetic axis, providing a strong molecular basis for AS-IV as a promising therapeutic agent against DN.