Infusion of mesenchymal stem cells ameliorates hyperglycemia in type 2 diabetic rats: identification of a novel role in improving insulin sensitivity

Abstract

Infusion of mesenchymal stem cells (MSCs) has been shown to effectively lower blood glucose in diabetic individuals, but the mechanism involved could not be adequately explained by their potential role in promoting islet regeneration. We therefore hypothesized that infused MSCs might also contribute to amelioration of the insulin resistance of peripheral insulin target tissues. To test the hypothesis, we induced a diabetic rat model by high-fat diet/streptozotocin (STZ) administration, performed MSC infusion during the early phase (7 days) or late phase (21 days) after STZ injection, and then evaluated the therapeutic effects of MSC infusion and explored the possible mechanisms involved. MSC infusion ameliorated hyperglycemia in rats with type 2 diabetes (T2D). Infusion of MSCs during the early phase not only promoted β-cell function but also ameliorated insulin resistance, whereas infusion in the late phase merely ameliorated insulin resistance. Infusion of MSCs resulted in an increase of GLUT4 expression and an elevation of phosphorylated insulin receptor substrate 1 (IRS-1) and Akt (protein kinase B) in insulin target tissues. This is the first report of MSC treatment improving insulin sensitivity in T2D. These data indicate that multiple roles and mechanisms are involved in the efficacy of MSCs in ameliorating hyperglycemia in T2D.

FIG. 1.

Infusion of MSCs ameliorates hyperglycemia in T2D rats in the early phase (7 days) and 42 days after STZ injection, respectively. Seven days after STZ injection, diabetic rats received 0.2 mL physiological saline or 2 × 10⁶ MSCs resuspended in 0.2 mL physiological saline, and the second MSC infusion was performed at 42 days after STZ injection. A: Blood glucose level was determined consecutively in alert, fasted rats using a glucometer-ACCU-CHEK Advantage Meter. d, day. Two weeks after MSC infusion, individual oral glucose tolerance was assessed by OGTTs, by intragastrically administering 2 mg glucose/g body weight and determining blood glucose levels (B); and insulin tolerance was evaluated by IPITTs, by injecting 2 g glucose/kg body weight immediately followed by insulin administration at a dose of 2 units/kg body weight (C). D: Individual insulin level in fasted and refed rats was evaluated by ELISA. E: Individual C-peptide level in fasted and refed rats was evaluated by ELISA. Values of A–E are means ± SE. n = 10 rats per group. *P < 0.05 and **P < 0.01.

FIG. 2.

Infusion of MSCs ameliorates hyperglycemia in T2D rats during the late phase after STZ injection. Twenty one days after STZ injection, diabetic rats received 0.2 mL physiological saline or 2 × 10⁶ MSCs resuspended in 0.2 mL physiological saline. A: Blood glucose level was determined consecutively in alert, fasted rats using a glucometer-ACCU-CHEK Advantage Meter. d, day. Two weeks after MSC infusion, individual glucose tolerance was assessed by OGTTs (B), and individual insulin tolerance was evaluated by IPITTs (C). D: Individual insulin level in fasted and refed rats was evaluated by ELISA. E: Individual C-peptide level in fasted and refed rats was evaluated by ELISA. Values of A–E are means ± SE. n = 10 rats per group. *P < 0.05 and **P < 0.01.

FIG. 3.

Infusion of MSCs promotes restoration of pancreatic islet function in T2D rats. A: Pancreas histology was studied in hematoxylin/eosin-stained sections, observed under light microscopy and focusing on islet structures indicated by arrows. Pancreatic islets were characterized by immunofluorescence according to the presence and distribution of insulin- (red) and glucagon-producing (green) cells in the T2D rats that received MSC infusion at 7 (B) or 21 days (C) after STZ injection. Pancreatic islets observed in hematoxylin/eosin-stained sections were quantified in the T2D rats that received MSC infusion at 7 (D) or 21 days (E) after STZ injection. β-Cells in pancreatic islets were quantified in the T2D and MSC-treated T2D rats that received MSC infusion at 7 (F) or 21 days (G) after STZ injection. Images were composite overlay of the individually stained nuclei, insulin and glucagon from the continuous pancreatic cryosections. Scale bar, 50 μm (A–C). Values of D–G are means ± SE. n = 5 sections per group. *P < 0.05 and **P < 0.01. (A high-quality digital representation of this figure is available in the online issue.)

FIG. 4.

Infusion of MSCs improved insulin sensitivity in T2D rats that received infusion at 7 or 21 days after STZ injection. A and B: Insulin sensitivity of each group was measured by euglycemic-hyperinsulinemic clamp. A: Exogenous GIR. All rats were infused with 8 mU/kg/min insulin during the hyperinsulinemic clamp. B: GDR of each group at insulin infusion rates of 8 mU/kg/min. C and D: HGP of each group at insulin infusion rates of 8 mU/kg/min, in the experiment in which MSC infusion was performed at 7 (C) or 21 days (D) after STZ injection. E and F: FBG and FINS concentrations of all rat groups were measured in blood collected at 2 weeks postinfusion by tail prick. E: HBCI of each group, HOMA-β (HBCI) = (20 × FINS [in units/L])/(FBG [in mmol/L] − 3.5). F: IR index of each group, HOMA-IR index = (FBG [in mmol/L] × FINS [in units/L])/22.5. Values of A–F are means ± SE. n = 10 rats per group. *P < 0.05 and **P < 0.01. d, day. DM, diabetes.

FIG. 5.

Infusion of MSCs increased the expression and membrane translocation of GLUT4 in skeletal muscle, adipose tissue, and liver. A: Total GLUT4 expression in muscle, adipose tissue, and liver and quantitative analysis of relative GLUT4 levels normalized to β-actin. B: Membrane translocation of GLUT4 and quantitative analyses of relative membrane GLUT4 levels normalized to Na⁺-K⁺-ATPase. Values are means ± SE. n = 10 rats per group. **P < 0.01.

FIG. 6.

MSC administration increased feeding-induced elevation of phosphorylated IRS-1 and Akt. The phosphorylated IRS-1 (Tyr⁶¹²) and Akt (Ser⁴⁷³) in the indicated tissues were measured by immunoblotting and were normalized by total IRS-1 and Akt, respectively. The normalized values in fasting normal groups were arbitrarily designated as 100%. Values are means ± SE. n = 10 rats per group. *P < 0.05 and **P < 0.01.