Hyperglycemia in combination with excess fat intake promotes renal pyroptosis and fibrosis through Gα12-dependent endoplasmic reticulum stress.

Background

Chronic exposure to free fatty acids (FFAs) and glucose may disrupt metabolic homeostasis and initiate pathological processes. This study investigated the effects of hyperglycemia and fat overload on renal endoplasmic reticulum (ER) stress, pyroptosis and fibrogenesis in mice and the underlying basis. We hypothesized that the combined insult would more severely induce Gα12-dependent ER stress and renal complications.

Methods

Mice were subjected to either high fat diet (HFD)+streptozotocin (STZ), or STZ treatment, and AZ2 was used as an anti-diabetic agent. Blood sera were used for blood biochemistry, and tissues were employed for RNA sequencing, immunoblottings, TEM, histology and immunohistochemistry. HEK293 and other cells were used for high glucose (HG) and palmitate treatment, or Gα12 or siGα12 transfection.

Results

The combined HFD and STZ treatment, showing enrichment of genes related to GPCR signaling, inflammasome, ER stress, and pyroptosis in the RNA-sequencing analysis, upregulated Gα12 in the kidney, alongside increased PGC1α and PPARα. IRE1α and ATF6 were elevated without an increase in GRP78. This was accompanied by elevated blood glucose, creatinine, and BUN levels. We also found increases of pro-IL-1β, IL-1β, caspase-1, and NLRP3, demonstrating pyroptosis. Immunoassays revealed increased fibrosis markers. AZ2 reversed these changes. STZ treatment alone exhibited mild complications in the absence of Gα12 induction despite severe hyperglycemia. In cell-based assays, HG+palmitate elicited IRE1 activation along with Gα12 overexpression although HG alone had a minimal effect. Overexpression of Gα12 facilitated the effect of HG+palmitate on ER stress, pyroptosis, and fibrosis, whereas Gα12 knockdown had the opposite effect, as corroborated by the outcomes obtained using STZ-treated Gα12-/-, Gα12+/-, and Gα13 liver-specific KO mice.

Conclusion

These findings support the role of HG and lipid overload combination in driving renal pyroptosis and fibrogenesis through Gα12-mediated ER stress and inflammasome, delineating the mechanism underlying the conditions of diabetic renal complications and pharmacological intervention.