Abstract 14763: Hypoxia-Mediated Activation of Notch Signaling Enhances Store-Operated Calcium Entry in Pulmonary Arterial Smooth Muscle Cells
Chronic exposure to hypoxia causes pulmonary vasoconstriction and vascular remodeling, which subsequently increase pulmonary vascular resistance (PVR) and pulmonary arterial pressure (PAP). Sustained vasoconstriction and augmented proliferation in pulmonary arterial smooth muscle cells (PASMC) are central to the pathogenesis of hypoxia-induced pulmonary hypertension (HPH). An increase in cytosolic Ca2+ concentration ([Ca2+]cyt) in PASMC is a major trigger for vasoconstriction as well as a key stimulus for cell proliferation and migration, both of which contribute to vascular remodeling. An important mechanism for controlling [Ca2+]cyt is store-operated Ca2+ entry (SOCE). Upon depletion of Ca2+ from the sarcoplasmic reticulum (SR), a Ca2+ deficiency signal in the SR is transmitted by STIM to store-operated Ca2+ channels (SOC) on the plasma membrane, causing SOC to open and Ca2+ to flow into the cytosol. TRPC6 and Orai1 channels both play an important role in SOCE in PASMC. Our previous studies have shown that Notch3 is upregulated in animals with HPH, and Notch signaling is important for controlling smooth muscle cell proliferation and differentiation. Therefore, we investigated Notch signaling and SOCE in response to hypoxia. Our data demonstrate that SOCE is enhanced and TRPC6/Orai1 channels are upregulated in PASMC exposed to hypoxia. We show that hypoxia not only increases expression of TRPC6/Orai1 but also activates Notch signaling, as indicated by increased expression of Notch intracellular domain (NICD). Additionally, inhibition of Notch signaling with DAPT (a γ-secretase inhibitor) attenuates hypoxia-mediated enhancement of SOCE in PASMC. We show that NICD functionally interacts with TRPC6 (and/or Orai1) and blockade of TRPC6 with 2-APB inhibits hypoxia-induced pulmonary vascular remodeling and HPH. These data suggest that Notch signaling enhances SOCE through direct interaction with TRPC6 resulting in increased [Ca2+]cyt which may contribute to the development of HPH. Understanding the molecular mechanisms which regulate [Ca2+]cyt and PASMC proliferation is critical to elucidation of the pathogenesis of HPH and the development of novel therapies for pulmonary hypertension associated with hypoxia.
- © 2012 by American Heart Association, Inc.