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Chronic mountain sickness (CMS) or Monge's disease is a disease in highlanders. These patients have a variety of neurologic symptoms such as migraine, mental fatigue, confusion, dizziness, loss of appetite, memory loss and neuronal degeneration. The cellular and molecular mechanisms underlying CMS neuropathology is not understood. In the previous study, we demonstrated that neurons derived from CMS patients' fibroblasts have a decreased expression and altered gating properties of voltage-gated sodium channel. In this study, we further characterize the electrophysiological properties of iPSC-derived astrocytes from CMS patients. We found that the current densities of the inwardly rectifying potassium (Kir) channels in CMS astrocytes (-5.7 ± 2.2 pA/pF at -140 mV) were significantly decreased as compared to non-CMS (-28.4 ± 3.4 pA/pF at -140 mV) and sea level subjects (-28.3 ± 5.3 pA/pF at -140 mV). We further demonstrated that the reduced Kir current densities in CMS astrocytes were caused by their decreased protein expression of Kir4.1 and Kir2.3 channels, while single channel properties (i.e., P o , conductance) of Kir channel in CMS astrocytes were not altered. In addition, we found no significant differences of outward potassium currents between CMS and non-CMS astrocytes. As compared to non-CMS and sea level subjects, the K + uptake ability in CMS astrocytes was significantly decreased. Taken together, our results suggest that down-regulation of Kir channels and the resulting decreased K + uptake ability in astrocytes could be one of the major molecular mechanisms underlying the neurologic manifestations in CMS patients., (Published by Elsevier Ltd.)

The sodium bicarbonate co-transporter (NBC) is the major bicarbonate-dependent acid-base transporter in mammalian astrocytes and has been implicated in ischemic brain injury. A malfunction of astrocytes could have great impact on the outcome of stroke due to their participation in the formation of blood-brain barrier, synaptic transmission, and electrolyte balance in the human brain. Nevertheless, the role of NBC in the ischemic astrocyte death has not been well understood. In this work, we obtained skin biopsies from healthy human subjects and had their fibroblasts grown in culture and reprogrammed into human-induced pluripotent stem cells (hiPSCs). These hiPSCs were further differentiated into neuroprogenitor cells (NPCs) and then into human astrocytes. These astrocytes express GFAP and S100β and readily propagate calcium waves upon mechanical stimulation. Using pH-sensitive dye BCECF [2',7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein] and qPCR technique, we have confirmed that these astrocytes express functional NBC including electrogenic NBC (NBCe). In addition, astrocytes exposed to an ischemic solution (IS) that mimics the ischemic penumbral environment enhanced both mRNA and protein expression level of NBCe1 in astrocytes. Using IS and a generic NBC blocker S0859, we have studied the involvement of NBC in IS-induced human astrocytes death. Our results show that a 30μM S0859 induced a 97.5±1.6% (n=10) cell death in IS-treated astrocytes, which is significantly higher than 43.6±4.5%, (n=10) in the control group treated with IS alone. In summary, a NBC blocker exaggerates IS-induced cell death, suggesting that NBC activity is essential for astrocyte survival when exposed to ischemic penumbral environment., (Published by Elsevier Ltd.)