Effect of Chronic High Altitude Hypoxia on Foetal and Maternal Juxta-Alveolar Distal Pulmonary Smooth Muscle Cells Actin and Calponin Organisation and Growth Profiles

Abstract

BACKGROUND:The effect of chronic high altitude hypoxia (CHAH) in the juxta-alveolar region near the air-blood interface is unknown because of the experimental inaccessibility of this region. OBJECTIVE: To examine primary cultures of digested juxtaalveolar smooth muscle cells for hypoxia-induced changes. METHODS: Smooth Muscle Cells (SMCs) obtained by dispase digestion of the extreme lung parenchyma were used to study the effect of CHAH in the juxta-alveolar region and foetal and maternal cells were compared. Pulmonary venous SMCs were also obtained from dissected 5 th to 7 th generation levels pulmonary veins (<0.5 mm). Fluorescence tagged antibodies against alpha smooth muscle actin (alpha SMA) and calponin respectively were used as markers to identify cellular structural differences by routine immunohistochemistry. Comparison of the functional integrity of the cells was made using their growth profiles obtained by radiolabeled thymidine incorporation and liquid scintillation counting. RESULTS: Marked differences were seen in juxta-alveolar SMCs obtained by digestion of extreme lung parenchyma of hypoxic sheep. Hypoxic adult sheep cells showed increased filamentation. Hypoxic foetal sheep cells showed internal restructuring and disorganization of both alpha-SMA and calponin filaments. The growth profiles of juxta-alveolar SMCs showed that the hypoxia-affected cells of both the foetus and adult sheep had a fast initial growth rate peaking at 48h while their normoxic equivalents had a steadier growth rate peaking at 72h. Hypoxia-affected cells showed contact inhibition at 50% subconfluence and apoptosis by 48h.

Comparative analysis of the mechanical signals in lung development and compensatory growth

“…Chronic hypoxia exposure or residence at high altitude has been reported to increase total pulmonary vessel length, volume, endothelial surface area and number of endothelial cells in vivo (Howell, et al, 2003). Cellular hypoxia impairs the mechanical function of contractile elements (Chen, et al, 2013, John, 2010, Moon, et al, 2010), which alters regional force distribution and deformation within and among cells. Hypoxia stimulates mitochondrial ROS generation, which stabilizes hypoxia-inducible transcriptional factor-1α (HIF-1α) (Chandel, et al, 2000, Guzy and Schumacker, 2006).…”