Pancreatic function in carboxyl-ester lipase knockout mice

Abstract

Background/aims: CEL-MODY is a monogenic form of diabetes and exocrine pancreatic insufficiency due to mutations in the carboxyl-ester lipase (CEL) gene. We aimed to investigate endocrine and exocrine pancreatic function in CEL knockout mice (CELKO).

Methods: A knockout mouse model with global targeted deletion of CEL was investigated physiologically and histopathologically, and compared to littermate control CEL+/+ mice at 7 and 12 months on normal chow and high-fat diets (HFD), i.e. 42 and 60% fat by calories.

Results: CELKO+/+ and -/- mice showed normal growth and development and normal glucose metabolism on a chow diet. Female CEL-/- mice on 60% HFD, on the other hand, had increased random blood glucose compared to littermate controls (p = 0.02), and this was accompanied by a reduction in glucose tolerance that did not reach statistical significance. In these mice there was also islet hyperplasia, however, α- and β-islet cells appeared morphologically normal and pancreatic exocrine function was also normal.

Conclusion: Although we observed mild glucose intolerance in female mice with whole-body knockout of CEL, the full phenotype of human CEL-MODY was not reproduced, suggesting that the pathogenic mechanisms involved are more complex than a simple loss of CEL function. and IAP.

Fig. 1

Expression of mouse CEL mRNA in CELKO and WT mice. CEL expression at the mRNA level in the pancreas of WT mice (white bar) and CEL–/– mice (CELKO; black bar) was assessed by quantitative real-time PCR.

Fig. 2

Weight and glucose homeostasis in CELKO and WT mice. Tail or hind leg vein blood was drawn in the random fed state at 9–11 a.m. and glucose was measured by glucometer. Plasma insulin was measured by ELISA. Results are given as mean ± SEM. WT, white bars and circles; CEL–/–, black bars and circles. a Male mice fed the 60% HFD had increased body weight compared to age-matched mice on chow (* p = 0.002 [CEL–/–], p = 0.02 [WT]), but there were no significant differences between CEL–/– and WT mice in either test group. b CEL–/– and WT mice were given a 60% HFD challenge for 12 weeks. There were no differences in rate of weight gain for either males or females, although CEL–/– males weighed borderline significantly less than controls at 3 weeks (p = 0.05). c Random fed glucose values were increased in the 60% HFD group compared to age-matched mice on chow for males (* p = 0.0004 [CEL–/–], p = 0.02 [WT]) and WT females (** p = 0.004). Random fed blood glucose was weakly, but statistically, increased in female CEL–/– mice compared to WT controls following a 60% HFD (*** p = 0.02).

Fig. 3

GTTs in CELKO and WT mice on chow or HFD. Open circles, WT; filled circles, CEL–/–. Results are given as mean ± SEM. A GTT was performed in (a) females and (b) males after a 12- to 14-hour fast by i.p. injection of glucose (2 g/kg b.w.). Although the 60% HFD induced decreased glucose tolerance compared to age-matched chow-fed mice, particularly in males, there were no differences between CEL–/– mice and controls in any group.

Fig. 4

ITTs in CELKO and WT female mice on chow or HFD. Open circles, WT; filled circles, CEL–/–. Results are given as mean ± SEM. An ITT was performed by i.p. injection of insulin (0.75 U/kg b.w.) in 12-month-old (a) and 7-month-old (b) mice. There were no differences between CEL–/– females and controls at either (a) chow diet (n = 5; left panel) or 42% HFD (n = 5; right panel), or (b) 60% HFD (n = 7; left panel). The 60% HFD induced insulin resistance in male mice (n = 8 CEL–/–, 10 WT; B, right panel), but no differences were detected between the genotypes.

Fig. 5

Insulin response and pancreatic morphology in CELKO and WT mice. An arginine-enhanced glucose-stimulated insulin secretion test was performed by the i.p. injection of a combination of 3 g/kg b.w. of glucose and 0.3 g/kg b.w. of arginine and collection of blood for insulin analysis at 0, 15, 30, and 60 min. Insulin was measured by ELISA. Results are given as mean ± SEM. Open circles, WT; filled circles, CEL–/–. No statistically significant differences were observed between chow-fed CEL–/– and in 12-month-old WT mice for random fed plasma insulin (a; graph shows results for females) or in an arginine-enhanced glucose-stimulated insulin secretion test (b, c; females, n = 5). Islet size and number as well as the organization of the exocrine pancreatic tissue was normal in HE-stained sections from CEL–/– male mice and not different from controls in either 12-month-old chow-fed mice (d) or in 7-month-old chow-fed mice after a 60% HFD (e) (10× resolution). f Triple immunohistochemical staining for insulin (blue), glucagon (red) and somatostatin (green) showed normal distribution of the corresponding endocrine β-, α- and δ-cell types in 12-month-old chow-fed males (40×).