Osteopontin is an endogenous modulator of the constitutively activated phenotype of pulmonary adventitial fibroblasts in hypoxic pulmonary hypertension

Abstract

Osteopontin is an endogenous modulator of the constitutively activated phenotype of pulmonary adventitial fibroblasts in hypoxic pulmonary hypertension. Am J Physiol Lung Cell Mol Physiol 303: L1-L11, 2012. First published May 11, 2012; doi:10.1152/ajplung.00050.2012.-Increased cell proliferation and migration, of several cell types are key components of vascular remodeling observed in pulmonary hypertension (PH). Our previous data demonstrate that adventitial fibroblasts isolated from pulmonary arteries of chronically hypoxic hypertensive calves (termed PH-Fibs) exhibit a "constitutively activated" phenotype characterized by high proliferative and migratory potential. Osteopontin (OPN) has been shown to promote several cellular activities including growth and migration in cancer cells. We thus tested the hypothesis that elevated OPN expression confers the "activated" highly proproliferative and promigratory/invasive phenotype of PH-Fibs. Our results demonstrate that, both in vivo and ex vivo, PH-Fibs exhibited increased expression of OPN, as well as its cognate receptors, ␣ V␤3 and CD44, compared with control fibroblasts (CO-Fibs). Augmented OPN expression in PH-Fibs corresponded to their high proliferative, migratory, and invasive properties and constitutive activation of ERK1/2 and AKT signaling. OPN silencing via small interfering RNA or sequestering OPN production by specific antibodies led to decreased proliferation, migration, invasion, and attenuated ERK1/2, AKT phosphorylation in PH-Fibs. Furthermore, increasing OPN levels in CO-Fibs via recombinant OPN resulted in significant increases in their proliferative, migratory, and invasive capabilities to the levels resembling those of PH-Fibs. Thus our data suggest OPN as an essential contributor to the activated (highly proliferative, migratory, and proinvasive) phenotype of pulmonary adventitial fibroblasts in hypoxic PH. vascular remodeling; inflammation; matricellular protein; extracellular matrix protein; vascular proliferation ALL FORMS OF CHRONIC PULMONARY hypertension (PH) are characterized by structural and fibroproliferative changes in both small and large pulmonary arteries (PAs) through a process termed vascular remodeling. Remodeling can affect all layers of the vessel wall and involves changes in the phenotype and functional behavior of each of the principal cell types in the vessel wall. However, one of the most consistent findings in experimental models of PH, as well as in models of vascular injury and hypertension in the systemic circulation, is early and dramatic adventitial remodeling, characterized by fibroblast proliferation, migration, and differentiation (5, 33, 53-55, 58, 64, 65). Although the mechanisms involved in these responses remain obscure, the possibility that they are coordinated through interactions with surrounding extracellular matrix (ECM) proteins is one possible mechanism (55, 58).

Tumor-Derived Osteopontin Reprograms Normal Mammary Fibroblasts to Promote Inflammation and Tumor Growth in Breast Cancer

“…This pathway specificity is further supported by the fact that blocking a v b 3 , but not CD44, could inhibit osteopontin-induced motility of fibroblasts. Indeed, a v b 3 was shown to contribute to osteopontin-induced fibroblast motility (45).…”

Osteopontin, a Key Mediator Expressed by Senescent Pulmonary Vascular Cells in Pulmonary Hypertension

“…19 Moreover, increased OPN expression has been documented in the lungs of chronically hypoxic calves and monocrotaline-treated rats. 20,21 We found that senescent cells stimulated the growth and migration of target PA-SMCs through 2 mechanisms, that is, the release of soluble factors and the release of ECM components. In our study, cell proliferation and migration in response to culture media from senescent cells or to matrix deposited by senescent cells were markedly reduced in the presence of neutralizing anti-OPN antibodies.…”

The Adventitia: Essential Regulator of Vascular Wall Structure and Function

“…Significant “imprinted” phenotypic differences have been reported in pulmonary AF derived from pulmonary hypertensive versus control animals, including far greater proliferative responses to pro-mitogenic stimuli including hypoxia, changes in the signaling pathways that elicit proliferation (18), and a marked pro-inflammatory phenotype characterized by increased production of chemokines, cytokines, matricellular proteins, and adhesion molecules (19, 20). Das et al have described significant changes in the functional role of the atypical PKCζ isozyme, such that it acted as a pro-proliferative kinase for AF from chronically hypoxic pulmonary hypertensive animals as opposed to its anti-proliferative actions in fibroblasts from normoxic controls (18).…”