Activation of farnesoid X receptor upregulates binding immunoglobulin protein expression and alleviates diabetic nephropathy

Abstract

BACKGROUND

The exact mechanisms underlying diabetic nephropathy (DN) remain incompletely elucidated, prompting researchers to explore new perspectives and identify novel intervention targets in this field.

AIM

To explore the role and underlying mechanisms of farnesoid X receptor (FXR) in the development of DN by regulating endoplasmic reticulum stress (ERS) molecular chaperone binding immunoglobulin protein (BiP) expression.

METHODS

Bioinformatics analyses identified potential FXR-binding elements in the BiP promoter. Dual-luciferase and chromatin immunoprecipitation (ChIP) assays confirmed FXR-BiP binding sites. In vitro studies used SV40 MES 13 cells under varying glucose conditions and treatments with FXR modulators [obeticholic acid (INT-747) and guggulsterones] or BiP small interfering RNA. The expression of BiP and ERS-related proteins [protein kinase R-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1 (IRE1), activating transcription factor 6 (ATF6)] was assessed alongside cell proliferation and extracellular matrix (ECM) synthesis. In vivo studies in DN mice (db/db) examined the effects of FXR activation on renal function and morphology.

RESULTS

FXR bound to the target sequence in the BiP promoter region, enhancing transcriptional activity, as confirmed by ChIP experiments. FXR expression decreased in SV40 MES 13 cells stimulated with high glucose and in renal tissues of DN mice compared with control. Treatment of SV40 MES 13 cells with the FXR agonist INT-747 significantly increased intracellular BiP expression, whereas silencing the FXR gene led to the downregulation of BiP levels. In vivo administration of INT-747 significantly elevated BiP levels in renal tissues, improved renal function and fibrosis in DN mice, while inhibiting the expression of ERS-related signaling proteins PERK, IRE1, and ATF6.

CONCLUSION

FXR promotes BiP expression by binding to its promoter, suppressing ERS pathways, and reducing mesangial cell proliferation and ECM synthesis. These findings highlight FXR as a potential therapeutic target for diabetic glomerulosclerosis.

Keywords: Binding immunoglobulin protein; Chromatin immunoprecipitation; Diabetic nephropathy; Endoplasmic reticulum stress; Farnesoid X receptor

Core Tip: What was known: Farnesoid X receptor (FXR) agonists alleviate proteinuria and glomerulosclerosis in diabetic nephropathy mice by inhibiting inflammation and oxidative stress. Hence, their protective effects have become a research focus in recent years. However, the specific targets and signaling pathways involved in their regulation remain unclear. This study adds: We demonstrated for the first time that using bioinformatics prediction, protein immunoprecipitation, and luciferase reporter assays that FXR directly binds to the promoter region of the binding immunoglobulin protein (BiP) gene. FXR activates the transcriptional activity of BiP, thereby explaining the molecular mechanism of FXR-regulated BiP transcription. We confirmed through in vitro experiments that FXR agonist obeticholic acid (INT-747) administration significantly promotes BiP expression in high-glucose-induced SV40 MES13 cells, while FXR inhibitors downregulated BiP expression. Potential impact: FXR has a direct regulatory effect on BiP. This study provides valuable insights regarding the prevention and treatment of diabetic nephropathy.