Heterogeneous Nuclear Ribonucleoprotein F Mediates Insulin Inhibition of Bcl2-Modifying Factor Expression and Tubulopathy in Diabetic Kidney

Abstract

We investigated the molecular mechanism(s) by which insulin prevents Bcl2-modifying factor (Bmf)-induced renal proximal tubular cell (RPTC) apoptosis and loss in diabetic mice. Transgenic mice (Tg) mice specifically overexpressing human BMF in RPTCs and non-Tg littermates were studied at 10 to 20 weeks of age. Non-diabetic littermates, diabetic Akita mice +/− insulin implant, Akita Tg mice specifically overexpressing heterogeneous nuclear ribonucleoprotein F (hnRNP F) in their RPTCs and immortalized rat renal proximal tubular cells (IRPTCs) were also studied. BMF -Tg mice exhibited higher systolic blood pressure, urinary albumin/creatinine ratio, RPTC apoptosis and urinary RPTCs than non-Tg mice. Insulin treatment in Akita mice and Akita mice overexpressing hnRNP F suppressed Bmf expression and RPTC apoptosis. In hyperinsulinemic-euglycemic wild type mice, renal Bmf expression was down-regulated with up-regulation of hnRNP F . In vitro , insulin inhibited high glucose-stimulation of Bmf expression, predominantly via p44/42 mitogen-activated protein kinase (MAPK) signaling. Transfection of p44/42 MAPK or hnRNP F small interfering RNA (siRNA) prevented insulin inhibition of Bmf expression. HnRNP F inhibited Bmf transcription via hnRNP F-responsive element in the Bmf promoter. Our results demonstrate that hnRNP F suppression of Bmf transcription is an important mechanism by which insulin protects RPTCs from apoptosis in diabetes.

Tubular Deficiency of Heterogeneous Nuclear Ribonucleoprotein F Elevates Systolic Blood Pressure and Induces Glycosuria in Mice

“…Semi-quantitation of the relative staining was done by NIH Image J software (http://rsb.info.nih.gov/ij/). Mean glomerular tuft and RPTC volumes, and the tubular luminal area were determined by the methods of Weibel 45 and Gundersen 46 , as described previously 47,48 .…”

Overexpression of Nrf2 in Renal Proximal Tubular Cells Stimulates Sodium–Glucose Cotransporter 2 Expression and Exacerbates Dysglycemia and Kidney Injury in Diabetic Mice

“…Generation of Akita Nrf2 À/À /NRF2 RPTC Tg Mice Tg mice specifically overexpressing rat Nrf2-Flag in their RPTCs were generated using a strategy similar to the method that we described previously for the generation of Agt RPTC , Cat RPTC , hnRNP F RPTC , and Bmf RPTC Tg mice (31)(32)(33)(34). The non-Akita wild type (WT) and Akita mice were born at and obtained from the same breeders.…”

“…SBP was monitored with a BP-2000 tail-cuff pressure monitor (Visitech Systems, Apex, NC) in the morning at least two to three times every 2 weeks for 8 weeks (25,(29)(30)(31)(32)(33)(34). Each animal was accustomed to the procedure for at least 15-20 min per day for 5 days before the first SBP measurement at week 10.…”

“…SBP values are presented as mean ± SEM of two to three determinations per mouse per group. GFR was estimated with FITC inulin, as recommended by the Animal Models of Diabetic Complications Consortium (https://www.diacomp.org) with slight modifications (25,33,34).…”

“…The mice were housed individually in metabolic cages for 6 h for urine collection. Urine samples were assayed for albumin and creatinine by albumin Exocell ELISA (Albuwell and Creatinine Companion; Ethos Biosciences, Philadelphia, PA) (25,(29)(30)(31)(32)(33)(34) and Ang II by ELISA (Bachem Americas, Torrence, CA) as described (35).…”