Histological investigation of murine pancreata from congenic mice for the investigation of two novel QTL for blood glucose

Background and aims:

This study took advantage of our previously detected Quantitative Trait Loci (QTL) for blood glucose identified on chromosomes 7 (designated Nbg7 p) and 15 (designated Nbg15 d) in a backcross of obese, diabetes-susceptible NZO with lean C3 H mice (Schallschmidt et al., Genetics 2018 210:1527). For both QTL, the C3 H-alleles were associated with lower blood glucose but higher plasma-insulin levels, indicating a protective function on pancreatic β-cells which were further investigated by the genotype-specific morphology.

Methods:

Mice from a recombinant-congenic strain carrying C3 H or NZO-alleles for Nbg7 p and Nbg15 d on NZO background were fed a high-fat diet (45 kcal% fat) and sacrificed at week 17 and 15 respectively. Paraffin-embedded pancreata (n = 3) were stained with hematoxylin and eosin for morphological analysis. Insulin staining, using DAB as chromogenic substrate, was conducted to determine pancreatic insulin content in islets.

Results:

For both QTL, C3 H-allele carriers demonstrated an overall increased islet number and area compared to NZO-allele carriers. Whereas in Nbg7pC3 H/C3 H mice larger islets (65,000 – 100,000 µm²) were detected, Nbg15dC3 H/C3 H animals showed higher amounts of smaller islets (0 – 10,000 µm²). Pancreatic insulin levels were increased in Nbg7pC3 H/C3 H compared to Nbg7pNZO/NZO mice, while a reverse pattern was found for Nbg15 d mice.

Conclusion:

The observed differences in islet number and size support our initial hypothesis that the C3 H-alleles of both QTL exert a protective effect on pancreatic islets, thereby preventing NZO mice from developing hyperglycemia. Further experiments will investigate glucose-stimulated insulin secretion of isolated islets from animals carrying NZO or C3 H-alleles at both loci.