The protection of Gαz-null NOD mice from hyperglycemia is sexually dimorphic and only partially β-cell autonomous

Abstract

The mechanisms that underlie the {beta}-cell pathophysiology of Type 1 Diabetes (T1D) are not fully understood. Our group has defined the unique heterotrimeric G protein alpha-subunit, Gz, as a key negative regulator of {beta}-cell signal transduction pathways. Non-obese diabetic (NOD) mice lacking Gz throughout the body are protected from developing T1D-like hyperglycemia. To determine whether this phenotype is {beta}-cell autonomous, we generated and validated a {beta}-cell-specific Gz knockout ({beta}KO) on the NOD background and characterized the phenotype of female and male cohorts. Long-term hyperglycemia incidence was lower in Gz {beta}KO mice as compared to wild-type (WT) controls, but, unlike global Gz knockout mice, this protection was incomplete. While young male and female Gz {beta}KO NOD mice had improved glucose tolerance, WT NOD males were significantly less glucose tolerant than females, and only female Gz {beta}KO mice retained improved glucose tolerance at 28-29 weeks of age. Conversely, {beta}-cell-specific Gz loss only influenced insulitis in 28-29-week old male NOD mice, a phenotype correlating directly with body burden of glucose during oral glucose challenge. Using surrogates for {beta}-cell function and apoptosis, the partial penetrance of euglycemia in Gz {beta}KO NOD was best explained by an early failure to up-regulate {beta}-cell proliferation. We conclude {beta}-cell Gz is an important regulator of the sexually-dimorphic T1D-like phenotype of NOD mice. Yet, other factors must be important in imparting full protection from the disease.