Adventitial Fibroblasts Induce a Distinct Proinflammatory/Profibrotic Macrophage Phenotype in Pulmonary Hypertension

Abstract

Macrophage accumulation is not only a characteristic hallmark but also a critical component of pulmonary artery (PA) remodeling associated with pulmonary hypertension (PH). However, the cellular and molecular mechanisms that drive vascular macrophage activation and their functional phenotype remain poorly defined. Utilizing multiple levels of in vivo (bovine and rat models of hypoxia-induced PH, together with human tissue samples) and in vitro (primary mouse, rat, and bovine macrophages, human monocytes, as well as primary human and bovine fibroblasts) approaches, we observed that adventitial fibroblasts derived from hypertensive Pas (bovine and human) regulate macrophage activation. These fibroblasts activate macrophages through paracrine IL6 and STAT3, HIF1, and C/EBPβ signaling to drive expression of genes previously implicated in chronic inflammation, tissue remodeling, and PH. This distinct fibroblast-activated macrophage phenotype was independent of IL4/IL13-STAT6 and TLR-MyD88 signaling. We found that genetic STAT3 haplodeficiency in macrophages attenuated macrophage activation while complete STAT3 deficiency increased macrophage activation through compensatory upregulation of STAT1 signaling, while deficiency in C/EBPβ or HIF1 attenuated fibroblast driven macrophage activation. These findings challenge the current paradigm of IL4/IL13-STAT6 mediated alternative macrophage activation as the sole driver of vascular remodeling in PH and uncover a crosstalk between adventitial fibroblasts and macrophages in which paracrine IL6 activated STAT3, HIF1, and C/EBPβ signaling is critical for macrophage activation and polarization. Thus, targeting IL6 signaling in macrophages by completely inhibiting C/EBPβ, HIF1a or partially inhibiting STAT3 may hold therapeutic value for treatment of PH and other inflammatory conditions characterized by increased IL6 and absent IL4/IL13 signaling.

Macrophage arginase-1 controls bacterial growth and pathology in hypoxic tuberculosis granulomas

“…Using this model, we identified Arg1 expression in lung granulomas analogous to those in TB patients and in NHP models of TB (11,38). Arg1-expressing cells surrounded the necrotic, hypoxic center of caseous granulomas, suggesting the hypoxic environment in this region potentially contributes to Arg1 induction (39,40,(47)(48)(49). As reported in human and NHP TB granulomas (11,38), inflammatory macrophages were the major cellular population expressing Arg1 in TB lung granulomas of Nos2 −/− mice.…”

Constitutive Reprogramming of Fibroblast Mitochondrial Metabolism in Pulmonary Hypertension

“…Thus, microenvironmental signals within the adventitia, in addition to hypoxia, are likely driving the PH-Fib phenotype. In addition, as we have previously shown for inflammatory macrophages, HIF1 signaling can be increased by a variety of factors (e.g., lactate, IL-6 [6,23,36]). However, the exact microenvironmental signals that induce and maintain cellular changes in metabolism remain elusive.…”

“…We have documented that, in both experimental hypoxic PH and human PH, the pulmonary artery adventitia harbors activated fibroblasts (hereafter termed PH-Fibs) with a hyperproliferative, apoptosis-resistant, and proinflammatory phenotype, which persists ex vivo over numerous passages in culture (15)(16)(17)(18)(19). Furthermore, in line with the paradigm that stromal cells play a critical role in initiation and perpetuation of vascular inflammation (14,(20)(21)(22), we have recently shown that PH-Fibs potently recruit, retain, and activate naive macrophages through paracrine signaling (17,23). However, at present, no studies have tested the hypothesis that abnormalities in mitochondrial metabolism drive the dramatic phenotypic changes observed in adventitial fibroblasts in PH, and even more importantly, if metabolic alterations can become imprinted and persist ex vivo.…”

Niclosamide Prevents Systemic Sclerosis in a Reactive Oxygen Species–Induced Mouse Model

“…Although the activation of STAT3 was first described in Th1 lymphocytes (44), increasing evidence suggests that this pathway plays a major role in Th2 lymphocyte differentiation (45)(46)(47). The Wnt/b-catenin pathway also stimulates Th2 differentiation, as well as IL-4 and IL-13 production, in human CD4 + T cells in a mouse model of allergic asthma (48,49).…”