(DCP007) DOES THE T2D-ASSOCIATED HNF1AG319S VARIANT CONFER A METABOLIC ADAPTATION TO FASTING?

Background: Genetic testing in Anishininew communities in central Canada led to the discovery of the HNF-1a G319S variant, which is strongly associated with youth-onset type 2 diabetes. Given the metabolic demand associated with traditional lifestyle practices, the G319S variant may instead confer an advantage to prolonged fasting, and/or diets low in carbohydrate. We hypothesize the G319S variant impairs insulin secretion when exposed to carbohydrate but is protective when consuming traditional off the land foods high in fat and protein.

METHODS AND RESULTS: CRISPR/Cas9 was used to knock in the G319S variant in C57BL6 mice, creating male and female wildtype (G/G), heterozygous (G/S), and homozygous (S/S) mice. Mice were weaned into a standard chow diet, a high protein and low-carbohydrate (HFLC) diet, or a high fat and high carbohydrate (HFHC) diet. At 3 months, mice were fasted for 24 hours and islets collected to assess insulin secretion capacity, gene expression and for electron micrography (EM) imaging.

When mice are fasted after fed a chow diet, there is decrease in insulin content (p=0.0094) and reduction of INS2 gene expression in S/S mice. EM images showed an increase percentage of immature insulin granules in S/S mice (p=0.0157) compared to G/G. There are no gene expression differences in typical maturation markers such as PDX1, UCN3, GK and PAX6, but there is upregulation of LDH and CPT1a in S/S mice. When mice are fasted after fed a HF/HC diet, Isolated islets show a reduction in GSIS capacity, but under a HF/LC diet, GSIS capacity is restored.

Conclusion: Our findings indicate that the HFHC diet accelerated metabolic dysfunction in G319S expression mice by decreasing insulin secretion capacity, whereas a HFLC diet prevented this dysfunction. In addition, S/S mice have greater immature insulin granules and gene expression changes that point toward decreased glucose metabolism but increased fatty acid oxidation.