Background/Purpose: Pulmonary arterial hypertension (PAH) is a severe lung complication of systemic sclerosis (SSc), and accounts for a large proportion of SSc-related deaths. As a manifestation of the SSc vasculopathy in pulmonary arteries, PAH is characterized by endothelial dysfunction, inflammation, and vascular wall remodeling. The transcription factor GATA6 is produced at high level in the normal pulmonary vasculature, including endothelial cells and smooth muscle cells, but its level is markedly reduced in both SSc-PAH and idiopathic PAH (IPAH) lungs. Furthermore, genetically modified mice that lack Gata6 in endothelial cells develop PAH spontaneously, suggesting that downregulation of GATA6 is an early and key event that leads to endothelial dysfunction and the development of PAH (Ghatnekar et al, 2013). Given that various stimuli induce endothelial dysfunction through the unfolded protein response (UPR) and autophagy pathways, we aim to test the hypothesis that GATA6 deficiency induces ER stress and autophagy in endothelial cells during the process of PAH development.

Methods: Sections of lung specimens from SSc-PAH patients were stained for BiP and CHOP, two major players of UPR pathways, by immunohistochemistry. The level of these two proteins were similarly tested in the lungs of two mouse models of PAH: chronic hypoxia-induced, and endothelial conditional knockout of GATA6 (GATA6 CKO). Expression of UPR and autophagy pathway genes in the lungs of these mouse models was measured by quantitative RT-PCR. GATA6 expression was blocked by siRNA in human pulmonary endothelial cells (HPAECs) cultured in vitro and the expression of UPR pathway genes was measured by quantitative RT-PCR. BiP and CHOP protein levels were also determined by western.

Results: BiP and CHOP levels were low in lung sections from healthy human subjects, but increased dramatically in the lungs of patients with SSc-PAH. Similarly, these two proteins were more abundant in the lungs from the two mouse models of PAH than in the lungs of wild-type mice. Specifically, BiP and CHOP were found in endothelial cells and macrophages in both human and mouse PAH lungs. In addition to BiP and CHOP, other UPR pathway genes such as PERK, ATF6, and XBP1, and autophagy markers LC3B, ATG3, ATG5, and ATG12 were also upregulated in murine lung by chronic hypoxia or loss of GATA6 from endothelial cells, but hypoxia treatment of GATA6 CKO mice did not have any additive effect on the expression of these genes. Consistent with the above in vivo data, deleting GATA6 in HPAECs with siRNA increased ATF4 mRNA level and BiP and CHOP protein levels in vitro.

Conclusion: GATA6 deficiency disrupts endothelial homeostasis and triggers a stress response, including the activation of UPR and autophagy pathways. Chronic activation of these pathways in endothelial cells contributes to the development of PAH.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/gata6-deficiency-activates-upr-pathways-in-endothelial-cells-during-the-development-of-pulmonary-arterial-hypertension/