Dipeptidyl peptidase IV inhibition with MK0431 improves islet graft survival in diabetic NOD mice partially via T-cell modulation

Abstract

Objective: The endopeptidase dipeptidyl peptidase-IV (DPP-IV) has been shown to NH2-terminally truncate incretin hormones, glucose-dependent insulinotropic polypeptide, and glucagon-like peptide-1, thus ablating their ability to potentiate glucose-stimulated insulin secretion. Increasing the circulating levels of incretins through administration of DPP-IV inhibitors has therefore been introduced as a therapeutic approach for the treatment of type 2 diabetes. DPP-IV inhibitor treatment has also been shown to preserve islet mass in rodent models of type 1 diabetes. The current study was initiated to define the effects of the DPP-IV inhibitor sitagliptin (MK0431) on transplanted islet survival in nonobese diabetic (NOD) mice, an autoimmune type 1 diabetes model.

Research design and methods: Effects of MK0431 on islet graft survival in diabetic NOD mice were determined with metabolic studies and micropositron emission tomography imaging, and its underlying molecular mechanisms were assessed.

Results: Treatment of NOD mice with MK0431 before and after islet transplantation resulted in prolongation of islet graft survival, whereas treatment after transplantation alone resulted in small beneficial effects compared with nontreated controls. Subsequent studies demonstrated that MK0431 pretreatment resulted in decreased insulitis in diabetic NOD mice and reduced in vitro migration of isolated splenic CD4+ T-cells. Furthermore, in vitro treatment of splenic CD4+ T-cells with DPP-IV resulted in increased migration and activation of protein kinase A (PKA) and Rac1.

Conclusions: Treatment with MK0431 therefore reduced the effect of autoimmunity on graft survival partially by decreasing the homing of CD4+ T-cells into pancreatic beta-cells through a pathway involving cAMP/PKA/Rac1 activation.

FIG. 1.

The effects of MK0431 in diabetic NOD mice after islet transplantation. A: Schematic diagram of group design. Islets isolated from nondiabetic NOD mice were infected with 250 MOI of rAD-TK, 200 of which were transplanted under the right kidney capsule of diabetic female NOD mice. Islet-transplanted diabetic NOD mice were fed as follows: group 1, normal chow diet throughout (NCD Tx); group 2, MK0431 diet after transplant (Post MK0431 Tx); group 3, MK0431 diet ∼1 month before and after transplant (Pre MK0431 Tx). B and C: The effects of MK0431 on plasma DPP-IV activity (B) and plasma active GLP-1 levels (C) in diabetic NOD mice after islet transplantation. D–I: The effects of MK0431 on food consumption (D), body weight (E), water intake (F), nonfasting (G) and fasting (H) glycemic control, and survival rates (I) in diabetic NOD mice after islet transplantation. Number of animals: n = 5∼7 per group: NCD Tx group (○), Post MK0431 Tx group (*), and Pre MK0431 Tx group (•). All data represent means ± SE, and significance was tested using ANOVA with a Newman-Keuls post hoc test, where **P < 0.05 vs. NCD Tx. □ and ○: NCD T. and *: Post MK0431 Tx. ▪ and •: Pre MK0431 Tx.

FIG. 1.

The effects of MK0431 in diabetic NOD mice after islet transplantation. A: Schematic diagram of group design. Islets isolated from nondiabetic NOD mice were infected with 250 MOI of rAD-TK, 200 of which were transplanted under the right kidney capsule of diabetic female NOD mice. Islet-transplanted diabetic NOD mice were fed as follows: group 1, normal chow diet throughout (NCD Tx); group 2, MK0431 diet after transplant (Post MK0431 Tx); group 3, MK0431 diet ∼1 month before and after transplant (Pre MK0431 Tx). B and C: The effects of MK0431 on plasma DPP-IV activity (B) and plasma active GLP-1 levels (C) in diabetic NOD mice after islet transplantation. D–I: The effects of MK0431 on food consumption (D), body weight (E), water intake (F), nonfasting (G) and fasting (H) glycemic control, and survival rates (I) in diabetic NOD mice after islet transplantation. Number of animals: n = 5∼7 per group: NCD Tx group (○), Post MK0431 Tx group (*), and Pre MK0431 Tx group (•). All data represent means ± SE, and significance was tested using ANOVA with a Newman-Keuls post hoc test, where **P < 0.05 vs. NCD Tx. □ and ○: NCD T. and *: Post MK0431 Tx. ▪ and •: Pre MK0431 Tx.

FIG. 2.

Time-course monitoring of glucose responses, plasma chemistry, and islet graft survival after islet transplantation. On the indicated days after transplantation, IPGTTs (A), plasma insulin (B), and glucagon (C) levels were determined in the mice described in the legend to Fig. 1A. Blood glucose levels were measured at 0, 15, 30, 60, 90, and 120 min after the glucose challenge (2 g/kg): NCD Tx group (○), Post MK0431 Tx group (*), and Pre MK0431 Tx group (•). D: Time-course monitoring of MicroPET signals detected from recipient diabetic mice after islet transplantation. Mice described in the legend to Fig. 1A were injected with [¹⁸F]FHBG on the indicated days after transplantation and scanned. Regions of interest were placed on the kidney area of the microPET image, and two peak values of percent ID/g from the two time activity curves for each region were used for determination of the signals. All data represent the mean ± SE, and significance was tested using ANOVA with a Newman-Keuls post hoc test, where **P < 0.05 vs. NCD Tx and ##P < 0.05 vs. 0 min, Pre MK0431 Tx. (Please see http://dx.doi.org/10.2337/db08-1101 for a high-quality digital representation of this figure.) □, NCD Tx; , Post MK0431 Tx; ▪, Pre MK0431 Tx. (Please see http://dx.doi.org/10.2337/db08-1101 for a high-quality digital representation of this figure.)

FIG. 3.

MK0431 regulates the migration of CD4⁺ T-cells. A: Schematic diagram of group design. Female NOD mice (8–10 weeks old) were placed on normal chow diet (NCD group) or MK0431 diet (MK0431 group) for 1 month. B: Nonfasting blood glucose levels. C: Representative pancreatic sections from 12- to 14-week-old littermate female NOD mice stained with H-E were shown. The extent of insulitis was assessed as described in research design and methods. D: Relative β-cell area. β-Cell area was expressed as the percentage of sectional pancreas area as described in research design and methods. E: CD4⁺ T-cells were isolated from the spleen of NCD and MK0431 group. The migration of CD4⁺ T-cells was determined using Transwell chamber as described in research design and methods. Correlation between migration of splenic CD4⁺ T-cells and plasma DPP-IV activity (F) and blood glucose levels (G). Data were analyzed using the linear regression analysis program PRISM. All data represent mean ± SE, and significance was tested using ANOVA with a Newman-Keuls post hoc test, where **P < 0.05 vs. normal NCD group and ##P < 0.05 vs. diabetic NCD group. (Please see http://dx.doi.org/10.2337/db08-1101 for a high-quality digital representation of this figure.)

FIG. 4.

Signaling modules potentially involved in the effect of MK0431 on splenic CD4⁺ T-cells. A: Rac1 GTP binding activity. Total cellular extracts were isolated from CD4⁺ T-cells described in Fig. 3 legend; Rac1 GTP binding activity was determined as described in research design and methods; and the data are expressed as fold difference vs. normal NCD group. Western blot analyses were performed with antibodies against phosphorylated p38MAPK (Thr180/Tyr182) (B), SAPK/JNK (Thr183/Tyr185) (C), p42/44 MAPK (Thr202/Tyr204) (D), PKB (Ser473) (E), PKB (Thr308) (F), and actin. Western blots are representative of n = 3, and significance was tested using ANOVA with a Newman-Keuls post hoc test, where **P < 0.05 vs. normal NCD group and ##P < 0.05 vs. diabetic NCD group.

FIG. 5.

The effect of sDPP-IV and incretins on splenic CD4⁺ T-cells. CD4⁺ T-cells were isolated from the spleen of nondiabetic female NOD mice placed on normal chow diet. T-cells were stimulated with purified porcine DPP-IV (100 mU/ml), GIP or GLP-1 (100 nmol/l) in the presence or absence of 100 μmol/l DPP-IV inhibitor for 1 h. A: Splenic CD4⁺ T-cell migration. The migration of splenic CD4⁺ T-cells were determined using Transwell chamber (Corning) as described in research design and methods. B: Rac1 GTP binding activity. Total cellular extracts were isolated, and Rac1 GTP binding activity was determined. C–G: Total cellular extracts were isolated, and Western blot analyses were performed with antibodies against phosphorylated p38MAPK (Thr180/Tyr182) (C), SAPK/JNK (Thr183/Tyr185) (D), p42/44 MAP Kinase (Thr202/Tyr204) (E), PKB (Ser473) (F), PKB (Thr308) (G), and actin. Western blots are representative of n = 3, and significance was tested using ANOVA with a Newman-Keuls post hoc test, where **P < 0.05 vs. control.

FIG. 6.

The effect of sDPP-IV on cAMP accumulation and the involvement of cAMP/PKA/Rac1 pathway in DPP-IV–mediated CD4⁺ T-cells migration. A: DPP-IV–mediated cAMP accumulation. Splenic CD4⁺ T-cells were stimulated for 30 min with GIP, 100 nmol/l GLP-1, or 100 mU/ml purified porcine DPP-IV in the presence of 0.5 mmol/l IBMX, and cAMP concentrations were determined in the cell extracts. B: Effect of MK0431 on DPP-IV–mediated PKA activation. Splenic CD4⁺ T-cells were treated with 100 mU/ml purified porcine DPP-IV in the presence of indicated concentration of MK0431, and PKA activity was determined. C: Effect of MK0431 on 6-Bnz-cAMP–mediated PKA activation. Splenic CD4⁺ T-cells were treated with 100 μmol/l 6-Bnz-cAMP in the presence of indicated concentration of MK0431, and PKA was activity determined. D: Effect of PKA inhibition on DPP-IV–mediated T-cell migration. CD4⁺ T-cells were stimulated for 1 h with 100 mU/ml DPP-IV or 10 μmol/l forskolin in the presence or absence of 10 μmol/l H-89, and cell migration was determined. E: Effect of PKA inhibition on DPP-IV–mediated Rac1 activation. CD4⁺ T-cells were treated as described above, and Rac1 GTP binding activity was determined. All data represent means ± SE, and significance was tested using ANOVA with a Newman-Keuls post hoc test, where **P < 0.05 vs. control and ##P < 0.05 vs. DPP-IV.