Kir4.1 channels contribute to astrocyte CO2/H+-sensitivity and the drive to breathe.

Astrocytes in the retrotrapezoid nucleus (RTN) stimulate breathing in response to CO2/H+, however, it is not clear how these cells detect changes in CO2/H+. Considering Kir4.1/5.1 channels are CO2/H+-sensitive and important for several astrocyte-dependent processes, we consider Kir4.1/5.1 a leading candidate CO2/H+ sensor in RTN astrocytes. To address this, we show that RTN astrocytes express Kir4.1 and Kir5.1 transcripts. We also characterized respiratory function in astrocyte-specific inducible Kir4.1 knockout mice (Kir4.1 cKO); these mice breathe normally under room air conditions but show a blunted ventilatory response to high levels of CO2, which could be partly rescued by viral mediated re-expression of Kir4.1 in RTN astrocytes. At the cellular level, astrocytes in slices from astrocyte-specific inducible Kir4.1 knockout mice are less responsive to CO2/H+ and show a diminished capacity for paracrine modulation of respiratory neurons. These results suggest Kir4.1/5.1 channels in RTN astrocytes contribute to respiratory behavior.

Effectiveness of Nicotinamide Phosphoribosyltransferase/Pre-B Cell Colony-enhancing Factor/Visfatin in preventing High Glucose-induced Neurotoxicity in an In-vitro Model of Diabetic Neuropathy.

Introduction: Diabetic neuropathy is a well-known complication of diabetes. Recently, hyperglycemia-induced toxicity has been confirmed to participates in multiple cellular pathways typical for neural deterioration. Nicotinamide phosphoribosyltransferase/pre-b cell colony-enhancing factor (Nampt/PBEF)/visfatin is a novel endogenous ligand that some studies have shown its neuroprotective effects on neurodegenerative disease. Therefore, we hypothesized that visfatin may prevent high glucose (HG)-induced neurotoxicity by inhibiting apoptosis, autophagy, and reactive oxygen species (ROS) responses properly. Methods: In this study, pheochromocytoma cell line 12 (PC12) cells were exposed to both HG concentrations (50, 75, 100, 125, 150 mM) and visfatin (50, 100, 150 ng/mL) at different time -points to determine the optimum time and dose of glucose and visfatin. To investigate the effects of visfatin on HG-induced damage in the PC12 diabetic neuropathy model, we examined ROS response, apoptosis, and autophagy using ROS detection kit, flow cytometry, and real-time PCR/Western blot, respectively. Results: We determined that HG concentration significantly increased the ROS level and apoptosis of diabetic PC12 cells. However, visfatin treatment significantly decreased the ROS production (P<0.05) and apoptosis of diabetic PC12 cells (P<0.0001). Beclin-1 messenger ribonucleic acid (mRNA) level (P<0.05) and light chain 3 (Lc3)-II protein level (P<0.05) showed that the autophagy pathway is impaired by HG concentrations. Conclusion: We concluded that visfatin can sufficiently decrease neural damage caused by ROS production and apoptosis under HG-induced toxicity. Highlights: High glucose significantly increased the ROS level and apoptosis of diabetic PC12 cells;The autophagy pathway is impaired by high glucose;Nampt/PBEF/visfatin can significantly reduce neural damage caused by ROS production and apoptosis of diabetic PC12 cells. Plain Language Summary: Diabetes mellitus is a metabolic disorder characterized by hyperglycemia resulting from a failure in insulin secretion, insulin action, or both. Visfatin (Nampt/PBEF) has insulin-mimetic effects. So far, no study has assessed its effects on diabetic neuropathy. Therefore, we examined the neuroprotective effects of visfatin on cell line 12 (PC12) against glucose-induced neurotoxicity. Based on the results, it was concluded that the Nampt/PBEF/visfatin can significantly reduce neural damage caused by production of reactive oxygen species and apoptosis of diabetic PC12 cell.