Effect of an acute glucose overload on Islet cell morphology and secretory function in the toad

Renal tubular damage may contribute more to acute hyperglycemia induced kidney injury in non-diabetic conscious rats

AIMS

Growing evidences suggest that acute hyperglycemia is strongly related to kidney injury. Our study aimed to investigate the effects of acute hyperglycemia on kidney glomerular and tubular impairment in non-diabetic conscious rats.

METHODS

Non-diabetic conscious rats were randomly subjected to 6h of saline (control group) or high glucose (acute hyperglycemia group) infusion. Blood glucose was maintained at 16.0-18.0 mmol/L in acute hyperglycemia group. Renal structure and function alterations, systemic/renal inflammation and oxidative stress markers were assessed, and apoptosis markers of renal inherent cells were evaluated.

RESULTS

Acute hyperglycemia caused significant injury to structure of glomerular filtration barrier, tubular epithelial cells and peritubular vascular endothelial cells. It increased urinary microalbumin (68.01 ± 27.09 μg/24h vs 33.81 ± 13.81 μg/24h , P=0.014), β2-microglobulin, Cystatin C, urinary and serous neutrophil gelatinase-associated lipocalin levels (P < 0.05). Acute hyperglycemia decreased megalin and cubilin expression, activated systemic and renal oxidative stress as well as inflammation and promoted renal inherent cell apoptosis.

CONCLUSIONS

Acute hyperglycemia causes significant injury to kidney function and structure. Compared with damages of glomerular filtration barrier, renal tubular injury may contribute more to acute hyperglycemia induced proteinuria. Activation of inflammation especially renal inflammation, oxidative stress and enhanced apoptosis may be the underlying mechanisms.

Down-regulation of Kir6.2 affects calcium influx and insulin secretion in HIT-T15 cells

In pancreatic beta cells, ATP-sensitive potassium (K(ATP)) channels are metabolic sensors that couple cell metabolism to electrical activity, and therefore K(ATP) channels regulate insulin secretion. We assume that down-regulating the expression of Kir6.2 subunits of K(ATP) channels may change calcium influx induced by glucose and insulin secretion regulated by K(ATP) channels. In our study, we employ Kir6.2-shRNA plasmid to downregulate Kir6.2 expression in HIT-T15 cells. Then, we research the effect of downregulation of Kir6.2 on K(ATP) current, cytoplasmic free Ca2+ concentration and insulin secretion. All results illustrate that downregulation of Kir6.2 subunits of K(ATP) channels in HIT-T15 cells affects K(ATP) current and insulin secretion, and fails to promote calcium influx. The results demonstrate the function of Kir6.2 subunits in electrophysiology characteristic, insulin secretion and calcium influx, and RNA interference provides a feasible alternative to study the function of Kir6.2 subunits in K(ATP) channels in different kinds of diabetes.

Proteomics and islet research

The complementary disciplines of genomics and proteomics offer better insights into the molecular mechanisms of diseases. While genomics hunts for defining our static genetic substrate, proteomics explores the structure and function of proteins expressed by a cell or tissue type under specified conditions. In the past decade, proteomics has been revolutionized by the application of techniques such as two-dimensional gel electrophoresis (2DGE), mass spectrometry (MS), and protein arrays. These techniques have tremendous potential for biomarker development, target validation, diagnosis, prognosis, and optimization of treatment in medical care, especially in the field of islet and diabetes research. This chapter will highlight the contributions of proteomic technologies toward the dissection of complex network of signaling molecules regulating islet function, the identification of potential biomarkers, and the understanding of mechanisms involved in the pathogenesis of diabetes.

Biological and Biomaterial Approaches for Improved Islet Transplantation

Islet transplantation may be used to treat type I diabetes. Despite tremendous progress in islet isolation, culture, and preservation, the clinical use of this modality of treatment is limited due to post-transplantation challenges to the islets such as the failure to revascularize and immune destruction of the islet graft. In addition, the need for lifelong strong immunosuppressing agents restricts the use of this option to a limited subset of patients, which is further restricted by the unmet need for large numbers of islets. Inadequate islet supply issues are being addressed by regeneration therapy and xenotransplantation. Various strategies are being tried to prevent beta-cell death, including immunoisolation using semipermeable biocompatible polymeric capsules and induction of immune tolerance. Genetic modification of islets promises to complement all these strategies toward the success of islet transplantation. Furthermore, synergistic application of more than one strategy is required for improving the success of islet transplantation. This review will critically address various insights developed in each individual strategy and for multipronged approaches, which will be helpful in achieving better outcomes.