We compared the evolution of insulin resistance, hyperglycemia, and pancreatic β-cell dysfunction in the Nile rat (Arvicanthis niloticus), a diurnal rodent model of spontaneous type 2 diabetes (T2D), when maintained on regular laboratory chow versus a high-fiber diet. Chow-fed Nile rats already displayed symptoms characteristic of insulin resistance at 2 months (increased fat/lean mass ratio and hyperinsulinemia). Hyperglycemia was first detected at 6 months, with increased incidence at 12 months. By this age, pancreatic islet structure was disrupted (increased α-cell area), insulin secretion was impaired (reduced insulin secretion and content) in isolated islets, insulin processing was compromised (accumulation of proinsulin and C-peptide inside islets), and endoplasmic reticulum (ER) chaperone protein ERp44 was upregulated in insulin-producing β-cells. By contrast, high-fiber-fed Nile rats had normoglycemia with compensatory increase in β-cell mass resulting in maintained pancreatic function. Fasting glucose levels were predicted by the α/β-cell ratios. Our results show that Nile rats fed chow recapitulate the five stages of progression of T2D as occurs in human disease, including insulinresistant hyperglycemia and pancreatic islet β-cell dysfunction associated with ER stress. Modification of diet alone permits long-term β-cell compensation and prevents T2D. 343-356229:3 β-cell phenotype in type 2 diabetic Nile rats k yang and others

Oxidative phosphorylation compensatory changes in the retina can be detected as early as 2 months, before development of hyperglycemia, and are associated with reduced mitochondrial outer membrane integrity.

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