Differences in long-term effects of standard rodent diets on blood glucose and body weight of offspring

Differentiation, reduction, and proliferation of pancreatic β-cells and their regulatory factors

The prevalence of diabetes has increased rapidly in recent years, and many types of therapeutic agents have been developed. However, the main purpose of these drugs is to lower blood glucose levels, and they are not fundamental solutions. In contrast, our research has been aimed at stimulating and inducing β-cell proliferation in vivo and replenishing β-cells. We demonstrated that pancreatic ductal cells are a source of β-cells both after birth and during regeneration after partial duct ligation: cell lineage tracing showed that 39% of growing islets and 50% of adult islets during tissue regeneration contained β-cells differentiated from duct cells. We also examined the factors contributing to β-cell depletion. Insulin and cyclin A genes are tightly regulated by transcriptional activators and repressors, and we found that imbalanced and excessive levels of repressors result in a drastic reduction of insulin and β-cell numbers, leading to severe diabetes. Thus, we searched for factors that induce β-cell proliferation in vivo. In our transgenic (Tg) mice, there was a sex difference in the progression of diabetes and sex steroid hormones were shown to contribute to this. Surprisingly, in diabetic male Tg mice, modulation of sex steroid hormones under certain conditions resulted in a marked increase of β-cells. We identified Greb1 as a factor inducing β-cell proliferation in response to a rapid elevation of E2 levels. This series of studies has demonstrated that islet cells exhibit plasticity and indicates that changes of islet cell mass and function are dynamic and recoverable.

Persistence and expansion of hypoxia detected by pimonidazole adduct immunostaining during progression of diabetic nephropathy in diabetic mice

Hypoxia and oxidative stress are considered to be underlying factors in the deterioration of renal function and pathogenesis in acute kidney injury (AKI) and chronic kidney disease, including diabetic nephropathy (DN). However, the long-term role of hypoxia in DN is unknown. Here, we investigated the distribution, severity, and time course of hypoxia during DN development in our well-established severely diabetic transgenic (Tg) DN mouse model that mimics human DN up to 80 wk of age, using pimonidazole adduct immunohistochemistry. The relationship between pimonidazole adduct distribution and hypoxia-inducible factor (HIF) expression was also examined. We found 1) persistent pimonidazole immunostaining mainly in the outer zone of the outer medulla, extending into the inner zone, 2) significant expansion of area and intensity up to 40 wk of age, and 3) characteristic subcellular localization mainly at apical sites in vesicular form by laser scanning microscopy of thin slices. The distribution of pimonidazole adducts was different from that of HIF reported previously, indicating that hypoxia does not directly contribute to persistent abnormal HIF expression. These results suggest that pimonidazole adducts produced under low [Formula: see text] conditions are sustained by a mechanism distinct from direct ischemia. We propose that in the long course of DN development, persistent hyperfiltration and hyperexcretion of glucose, albumin, and water increase metabolism and energy expenditure in the tubules, and such chronic stimulation leads to relative ischemia and local hypoxia, which may contribute in part to the loss of nephrons.NEW & NOTEWORTHY This study provides new insights into hypoxia during the long course of diabetic nephropathy development. Hypoxia was persistently localized only in limited areas and its distribution differed significantly from that of hypoxia-inducible factors. These findings suggests that in the long course of diabetic nephropathy development, increased energy requirements and limited blood supply may lead to relative ischemia and induction of local and persistent hypoxia, which may contribute in part to the loss of nephrons.

Greb1 Transiently Accelerates Pancreatic β-Cell Proliferation in Diabetic Mice Exposed to Estradiol

Decrease of pancreatic β cells leads to diabetes. In an inducible cAMP early suppressor (ICER-Iγ) transgenic mouse model of severe type 2 diabetes with reduced insulin production and depleted β cells, supplementation with high concentrations of 17β-estradiol (E2) markedly enhances β-cell proliferation and normalizes glucose levels. The current study explored the underlying mechanisms leading to a dynamic increase of β cells and pathologic changes in diabetic mice exposed to E2. Gene expression profiling of pancreatic islets of 6-month-old ICER-transgenic mice recovering from diabetes due to elevated E2 levels identified growth regulation by estrogen in breast cancer 1 (Greb1) as a gene significantly up-regulated during the recovery phase. To substantiate this, β-cell-specific Greb1-deficient mice were generated, and Greb1 was shown to be essential for recovery of depleted β cells in diabetic mice. Graft growth and glucose lowering were observed in 50 islets with increased Greb1 expression transplanted adjacent to E2 pellets beneath the kidney capsule of streptozotocin-induced diabetic mice. Greb1 expression due to a drastic increase in exogenous or endogenous E2 was transient and closely correlated with changes in E2-related and some cell cycle-related genes. These findings provide new insights into in vivo proliferation of deficient β cells and suggest the possibility of new therapeutic approaches targeting pancreatic β cells that could revolutionize the concept of diabetes treatment, which has been considered difficult to cure completely.

Amelioration of Murine Diabetic Nephropathy with a SGLT2 Inhibitor Is Associated with Suppressing Abnormal Expression of Hypoxia-Inducible Factors

Diabetic nephropathy (DN), once manifested, is unlikely to completely recover. Factors that influence DN progression were explored by investigating the process of glomerulosclerosis and interstitial fibrosis and chronological changes in glucose, albuminuria, hyperfiltration, and expressions of sodium-glucose cotransporter 2 (SGLT2) and hypoxia-inducible factors (HIFs) up to 50 weeks in inducible cAMP early repressor transgenic mice, a model of severe DN. Long-term intervention with the SGLT2 inhibitor canagliflozin or islet transplantation or heminephrectomy was used. Inducible cAMP early repressor transgenic mice exhibited progressive diabetic glomerulosclerosis and mild interstitial fibrosis, and expressed extensive HIF-1α and HIF-2α in glomerulus and tubules, with sustained hyperfiltration up to 50 weeks. Canagliflozin ameliorated glomerulosclerosis/interstitial fibrosis gradually and reduced HIF overexpression. Islet-transplanted mice exhibited no amelioration. None of the heminephrectomized diabetic mice survived the hyperfiltration overload, but all of the canagliflozin-treated mice survived with re-expressions of HIF-1α and HIF-2α. These results suggest that persistent glomerular hyperfiltration might initiate glomerular injury, and persistent overexpression of HIFs could promote the development of glomerulosclerosis and interstitial fibrosis. Canagliflozin attenuated both changes. Oxidative stress or hypoxia was undetectable in this model. The abnormal expression of HIF-1α and HIF-2α may be a potential therapeutic target for preventing glomerulosclerosis and interstitial fibrosis.