Mesenchymal stem cell-conditioned medium alleviates high fat-induced hyperglucagonemia via miR-181a-5p and its target PTEN/AKT signaling

Highlights

• bmMSC-CM infusion protected against HFD-induced hyperglycemia and hyperglucagonemia in vivo.

• bmMSC-CM decreased glucagon secretion, accompanied by reduction of PTEN expression and restoration of AKT signaling.

• miR-181a-5p secreted by BM-MSCs was involved in regulating glucagon secretion via PTEN/AKT signaling.

Abstract

Background

α-cell dysregulation gives rise to fasting and postprandial hyperglycemia in type 2 diabetes mellitus(T2DM). Administration of Mesenchymal stem cells (MSCs) or their conditioned medium can improve islet function and enhance insulin secretion. However, studies showing the direct effect of MSCs on islet α-cell dysfunction are limited.

Methods

In this study, we used high-fat diet (HFD)-induced mice and α-cell line exposure to palmitate (PA) to determine the effects of bone marrow-derived MSC-conditioned medium (bmMSC-CM) on glucagon secretion. Plasma and supernatant glucagon were detected by enzyme-linked immunosorbent assay(ELISA). To investigate the potential signaling pathways, phosphatase and tensin homolog deleted on chromosome 10 (PTEN), AKT and phosphorylated AKT(p-AKT) were assessed by Western blotting.

Results

In vivo, bmMSC-CM infusion improved the glucose and insulin tolerance and protected against HFD-induced hyperglycemia and hyperglucagonemia. Meanwhile, bmMSC-CM infusion ameliorated HFD-induced islet hypertrophy and decreased α- and β-cell area. Consistently, in vitro, glucagon secretion from α-cells or primary islets was inhibited by bmMSC-CM, accompanied by reduction of intracellular PTEN expression and restoration of AKT signaling. Previous studies and the TargetScan database indicate that miR-181a and its target PTEN play vital roles in ameliorating α-cell dysfunction. We observed that miR-181a-5p was highly expressed in BM-MSCs but prominently lower in αTC1-6 cells. Overexpression or downregulation of miR-181a-5p respectively alleviated or aggravated glucagon secretion in αTC1-6 cells via the PTEN/AKT signaling pathway.

Conclusions

Our observations suggest that MSC-derived miR-181a-5p mitigates glucagon secretion of α-cells by regulating PTEN/AKT signaling, which provides novel evidence demonstrating the potential for MSCs in treating T2DM.

Introduction

Pronounced changes in lifestyle and environment have made type 2 diabetes mellitus (T2DM) a global health issue. Among adults in China, the estimated overall prevalence of diabetes is 10.9%, and that for prediabetes is 35.7% (Wang et al., 2017a). T2DM is characterized by dysfunction of pancreatic β-cells and insulin resistance. Nevertheless, α-cells cannot be underestimated because their function to release glucagon and stimulate the liver to produce glucose (Baetens et al., 1979). Dysregulation of α-cells results in fasting and postprandial hyperglycemia in T2DM (Dunning and Gerich, 2007) and is accompanied by a higher glucagon-to-insulin ratio and augmentation of the pancreatic α-to β-cell area ratio (Fujita et al., 2018; Lee et al., 2019). In addition, enhanced glucagon concentrations is also observed in prediabetes population(Sharma et al., 2018). Fasting glucagon concentrations are associated with a longitudinal decline of β-cell function in non-diabetics (Adams et al., 2020).

Free fatty acids increase glucagon secretion from α-cell lines and primary islets (Hong et al., 2007; Bollheimer et al., 2004; Olofsson et al., 2004; Collins et al., 2008; Piro et al., 2010). α-Cells exposed to fatty acids exhibit insulin resistance, manifested as impaired IRS-1/PI3K/Akt pathway, which participates in glucagon secretion regulation (Piro et al., 2010). Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a potent negative regulator of the PI3K/AKT pathway. Its deletion in pancreatic α-cells alleviates high-fat diet (HFD)-induced hyperglucagonemia and insulin resistance (Wang et al., 2015).

Stem cell-based therapy has been considered as a promising treatment for diabetes(Xv et al., 2017). Mesenchymal stem cells (MSCs) can be obtained from bone marrow, adipose tissue and umbilical cord, which plays increasingly important roles in regenerative medicine(Shi et al., 2017; Si et al., 2012a). Several recent clinical trials have indicated that MSCs-based therapies are effective in decreasing blood glucose and alleviating some complications, such as diabetic foot injuries and diabetic retinopathy (Wehbe et al., 2016; Bhansali et al., 2017; Li et al., 2017; Dong et al., 2017; Cil et al., 2017). MSCs or their conditioned medium and exosomes not only ameliorate pancreatic β-cell injury (Liu et al., 2018; Zhao et al., 2015), islet endothelium apoptosis, and functional impairment (Wang et al., 2017b), but also improve hepatic glucose and lipid metabolism and enhance sensitivity of insulin target tissues (Qin et al., 2020; Si et al., 2012b; Sun et al., 2017; Xie et al., 2016). However, studies showing the direct effect of MSCs on pancreatic α-cell dysfunction are limited. An increasing number of studies indicate that the rationale for MSC therapy is based on its paracrine action rather than its differentiation mechanism (Liang et al., 2014; Weil et al., 2009; Spees et al., 2016). MicroRNAs (miRNAs) are important factors secreted by MSCs, which regulate gene expression at the post-transcriptional level and play critical roles in regulating differentiation, paracrine action, and other cellular activities (Si et al., 2012b). Based on these reports, we hypothesize that MSCs could improve the function of pancreatic α-cells by secreting miRNAs.

Therefore, in this study, we used HFD-induced mice and α-cell line exposure to PA to investigate the effects and mechanisms of bone marrow-derived MSCs conditioned medium (bmMSC-CM) in relation to glucagon secretion.