Metformin overcomes high glucose-induced insulin resistance of podocytes by pleiotropic effects on SIRT1 and AMPK

Abstract

Podocyte insulin sensitivity is critical for glomerular function, and the loss of appropriate insulin signaling leads to alterations and disorders featuring diabetic nephropathy. Energy-sensing pathways, such as AMP-dependent protein kinase (AMPK) and protein deacetylase SIRT1, have been shown to play an important role in insulin resistance. The absence of a stimulating effect of insulin on glucose uptake into podocytes after exposure to hyperglycemic conditions has been demonstrated to be related to a decreased level and activity of SIRT1 protein, leading to reduced AMPK phosphorylation. The present work was undertaken to investigate metformin's ability to restore the insulin responsiveness of podocytes by regulating SIRT1 and AMPK activities. Primary rat podocytes cultured with standard or high glucose concentrations for 5days were transfected with siRNAs targeting SIRT1, AMPKα1, or AMPKα2. SIRT1 activity was measured by a fluorometric method. Insulin-stimulated changes in glucose uptake were used to detect insulin resistance. Podocyte permeability was measured by a transmembrane albumin flux assay to examine podocytes functioning. Our results demonstrated that metformin activated SIRT1 and AMPK, prevented hyperglycemia-induced reduction of SIRT1 protein levels, ameliorated glucose uptake into podocytes, and decreased glomerular filtration barrier permeability. Furthermore, metformin activated AMPK in a SIRT1-independent manner, as the increase in AMPK phosphorylation after metformin treatment was not affected by SIRT1 downregulation. Therefore, the potentiating effect of metformin on insulin-resistant podocytes seemed to be dependent on AMPK, as well as SIRT1 activity, establishing multilateral effects of metformin action.

SHIPping out diabetes—Metformin, an old friend among new SHIP2 inhibitors

“…In rats with T2D, metformin increases the expression of nephrin and podocalyxin, both known to be downregulated or mislocalized in DKD . Treatment of primary rat podocytes with metformin activates protein deacetylase sirtuin 1 (SIRT1) and AMPK, and prevents high glucose‐induced downregulation of SIRT1 expression . Metformin also reduces high glucose‐induced apoptosis of podocytes in vitro .…”

Metformin inhibits high glucose‐induced mesangial cell proliferation, inflammation and ECM expression through the SIRT1‐FOXO1‐autophagy axis

“…Our previous work indicated that metformin inhibits the in vitro expression of inflammatory cytokines and activation of nuclear factor‐κB induced by high glucose in rat glomerular mesangial cells. Emerging studies have shown that metformin can improve the blood glucose levels of DM patients through activating AMP‐activated protein kinase (AMPK), which also activates SIRT1 and regulates energy metabolism through FOXO1 . Wang et al revealed that although high glucose reduces the SIRT1 level and increases inflammatory factor expression in mesangial cells, SIRT1 activation downregulates the transcriptional activity of nuclear factor‐kappaB (NF‐κB) and inhibits inflammatory factor production and improves the inflammatory response in the kidney …”

“…Emerging studies have shown that metformin can improve the blood glucose levels of DM patients through activating AMP-activated protein kinase (AMPK), which also activates SIRT1 and regulates energy metabolism through FOXO1. 14 Wang et al 15 revealed that although high glucose reduces the SIRT1 level and increases inflammatory factor expression in mesangial cells, SIRT1 activation downregulates the transcriptional activity of nuclear factor-kappaB (NF-κB) and inhibits inflammatory factor production and improves the inflammatory response in the kidney. 15 The present work explores the role of metformin in mesangial cell proliferation, inflammation and ECM accumulation induced by high glucose and elucidates the underlying mechanism of metformin function on SIRT1/FOXO1-mediated autophagy to provide new insight into the development of DN.…”

Salidroside ameliorates diabetic nephropathy in rats by activating renal AMPK/SIRT1 signaling pathway

“…Of interest, AMPK and SIRT1 levels and activities were significantly declined in the kidneys T1DM, T2DM, and metabolic animal models and were correlated with the higher levels of ROS, apoptosis, and renal damage, whereas their activation afforded renoprotection (Declèves et al, ; Dugan et al, ; Eid et al, ; Lee et al, ; Piwkowska et al, ; Rogacka et al, , ; Xue et al, ; Yao et al, ; Zhang et al, ). These findings were also confirmed in the kidneys of our diabetic rats and in the HG‐treated mesangial cells.…”

“…Interestingly, AMPK levels and activities were significantly suppressed in the kidneys of diabetic patients and animals and were positively correlated with the severity of the degree of the DN, renal damage, and the clinical symptoms (Bandyopadhyay, Yu, Ofrecio, & Olefsky, 2006;Declèves, Mathew, Cunard, & Sharma, 2011;Eid et al, 2010;Lee et al, 2007;Rogacka, Piwkowska, Audzeyenka, Angielski, & Jankowski, 2014;Rogacka et al, 2018;Xu et al, 2012;Vitale, Mercuro, Silvestri, Fini, & Rosano, 2003). However, pharmacological activation of AMPK improved renal function, and attenuated the clinical-pathological features of DN in patients and experimental animals through reducing ROS levels, stimulating fatty acids oxidation, and inhibition of cellular inflammation, fibrosis, and apoptosis (Szrejder & Piwkowska, 2019).…”