adenosine-kinase and Hyperglycemia

Severe reduction in the β-cell number (collectively known as the β-cell mass) contributes to the development of both type 1 and type 2 diabetes. Recent pharmacological studies have suggested that increased pancreatic β-cell proliferation could be due to specific inhibition of adenosine kinase (ADK). However, genetic evidence for the function of pancreatic β-cell ADK under physiological conditions or in a pathological context is still lacking. In this study, we crossed mice carrying LoxP-flanked Adk gene with Ins2-Cre mice to acquire pancreatic β -cell ADK deficiency (Ins2-Cre

Topics: Adenosine Kinase; Aging; Animals; Cell Count; Cell Proliferation; Gene Deletion; Glucose; Homeostasis; Hyperglycemia; Insulin-Secreting Cells; Mice, Knockout; Streptozocin; Time Factors

The early stages of diabetic retinopathy (DR) are characterized by alterations similar to neurodegenerative and inflammatory conditions such as increased neural apoptosis, microglial cell activation and amplified production of pro-inflammatory cytokines. Adenosine regulates several physiological functions by stimulating four subtypes of receptors, A1AR, A2AAR, A2BAR, and A3AR. Although the adenosinergic signaling system is affected by diabetes in several tissues, it is unknown whether diabetic conditions in the retina can also affect it. Adenosine delivers potent suppressive effects on virtually all cells of the immune system, but its potential role in the context of DR has yet to be studied in full. In this study, we used primary mixed cultures of rat retinal cells exposed to high glucose conditions, to mimic hyperglycemia, and a streptozotocin rat model of type 1 diabetes to determine the effect diabetes/hyperglycemia have on the expression and protein levels of adenosine receptors and of the enzymes adenosine deaminase and adenosine kinase. We found elevated mRNA and protein levels of A1AR and A2AAR, in retinal cell cultures under high glucose conditions and a transient increase in the levels of the same receptors in diabetic retinas. Adenosine deaminase and adenosine kinase expression and protein levels showed a significant decrease in diabetic retinas 30 days after diabetes induction. An enzymatic assay performed in retinal cell cultures revealed a marked decrease in the activity of adenosine deaminase under high glucose conditions. We also found an increase in extracellular adenosine levels accompanied by a decrease in intracellular levels when retinal cells were subjected to high glucose conditions. In conclusion, this study shows that several components of the retinal adenosinergic system are affected by diabetes and high glucose conditions, and the modulation observed may uncover a possible mechanism for the alleviation of the inflammatory and excitotoxic conditions observed in diabetic retinas.

Topics: Adenosine; Adenosine Deaminase; Adenosine Kinase; Animals; Cells, Cultured; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Glucose; Hyperglycemia; Male; Rats; Rats, Wistar; Receptors, Purinergic P1; Retina

The proliferative response of T lymphocytes is a crucial step in cell-mediated immunity. This study was undertaken to investigate the mechanisms leading to the impaired proliferative response of diabetic T lymphocytes. T cells that had been isolated from the spleen of normal rats and cultured in medium containing 20 mm glucose and no insulin displayed the same degree of proliferative impairment as cells isolated from diabetic rats. The rate of T-cell proliferation, when induced with concanavalin A or anti-CD3 and anti-CD28 antibodies, was not affected by the inhibition of nucleoside transporters. T cells cultured at high glucose concentrations in the absence of insulin displayed decreased expression of adenosine kinase, and released measurable extracellular quantities of adenosine. Under resting conditions, the level of cAMP was 5.9-fold higher in these cells compared to cells grown in low glucose and in the presence of insulin. Experiments with specific adenosine receptor agonists and antagonists showed that adenosine-induced suppression of diabetic T cell proliferation was mediated by the A2A adenosine receptor, but not by the A2B receptor. Treatment of diabetic T cells with 10 microm H-89, a specific protein kinase A inhibitor, restored T-cell proliferation. These results show that suppressed proliferation of diabetic T lymphocytes is evoked by the decreased expression of adenosine kinase, leading to the outflow of adenosine from the cell. Extracellular adenosine then stimulates the A2A receptor and induces cAMP production, leading to the activation of protein kinase A, and suppression of T-cell proliferation.

Topics: Adenosine Kinase; Animals; Cell Proliferation; Cells, Cultured; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Diabetes Mellitus, Experimental; Gene Expression Regulation; Hyperglycemia; Immune Tolerance; Immunity, Cellular; Insulin; Male; Nucleoside Transport Proteins; Protein Kinase Inhibitors; Rats; Rats, Wistar; Receptor, Adenosine A2A; Receptors, Purinergic P1; RNA, Messenger; Signal Transduction; Spleen; T-Lymphocytes