Reduced Insulin Receptor Expression Enhances Proximal Tubule Gluconeogenesis

Abstract

Reduced insulin receptor protein levels have been reported in the kidney cortex from diabetic humans and animals. We recently reported that, targeted deletion of insulin receptor (IR) from proximal tubules (PT) resulted in hyperglycemia in non-obese mice. To elucidate the mechanism, we examined human proximal tubule cells (hPTC) and C57BL/6 mice fed with high-fat diet (HFD, 60% fat for 20 weeks). Immunoblotting revealed a significantly lower protein level of IR in HFD compare to normal chow diet (NCD). Furthermore, a blunted rise in p-AKT levels in the kidney cortex of HFD mice was observed in response to acute insulin (0.75 IU/kg body weight, i.p) relative to NCD n = 8/group, P < 0.05). Moreover, we found significantly higher transcript levels of phosphoenolpyruvate carboxykinase (PEPCK, a key gluconeogenic enzyme) in the kidney cortex from HFD, relative to mice on NCD. The higher level of PEPCK in HFD was confirmed by immunoblotting. However, no significant differences were observed in cortical glucose-6-phosphatase (G6Pase) or fructose-1,6, bisphosphosphatase (FBPase) enzyme transcript levels. Furthermore, we demonstrated insulin inhibited glucose production in hPTC treated with cyclic AMP and dexamethasone (cAMP/DEXA) to stimulate gluconeogenesis. Transcript levels of the gluconeogenic enzyme PEPCK were significantly increased in cAMP/DEXA-stimulated hPTC cells (n = 3, P < 0.05), and insulin attenuated this upregulation Furthermore, the effect of insulin on cAMP/DEXA-induced gluconeogenesis and PEPCK induction was significantly attenuated in IR (siRNA) silenced hPTC (n = 3, P < 0.05). Overall the above data indicate a direct role for IR expression as a determinant of PT-gluconeogenesis. Thus reduced insulin signaling of the proximal tubule may contribute to hyperglycemia in the metabolic syndrome via elevated gluconeogenesis. J. Cell. Biochem. 118: 276-285, 2017. © 2016 Wiley Periodicals, Inc.

miR-451 Loaded Exosomes Are Released by the Renal Cells in Response to Injury and Associated With Reduced Kidney Function in Human

“…Inhibition of miR-451 by locked nucleic acid (LNA) was, however, not achieved in podocytes even at the highest recommended dose of LNA. Phenotypic and functional characterization of hPT cells cultured from human kidney tissues have previously published by us (Pandey et al, 2017). The downregulation of miR-451 in hPT cells by LNA inhibitor was confirmed by real-time PCR, which showed a significant decrease in miR-451 expression as compared to LNA-miR-451a inhibitor control-transfected cells (negative control) (Figure 3).…”

“…Human primary proximal tubule (hPT) cells were cultured and characterized from human kidney we previously described (Pandey et al, 2017).…”

Effect of Insulin on Proximal Tubules Handling of Glucose: A Systematic Review

“…In accordance, PT cells from human nephrectomies [176] and HK2 cell cultures [4] exposed to insulin undergo gluconeogenesis reduction. However, a high gluconeogenic enzyme content in human renal biopsies from T2D was reported [46] which could be interpreted as an impairment of insulin action on kidneys, maybe a kidney-specific insulin resistance.…”

“…Insulin action on the sympathetic system can, indirectly, modulate SGLT2, hence changing glucose handling [22]. In addition, renal gluconeogenesis is enhanced in diabetes [4,14,46,67,110,[173][174][175][176][177] and is inhibited by insulin [4,179], which could influence glucose reabsorption through SGLT2 [21,22].…”

“…Renal gluconeogenesis is enhanced in STZ rats [4,14,46,67,110,173], in murine model knockout for IRecs [174] or IRS1 plus IRS2 [4], in a mix model of high-fat diet plus STZ [175], and in T2D murine models [176,177] demonstrating the essential insulin role.…”