Evidence for cell fusion is absent in vascular lesions associated with pulmonary arterial hypertension

Abstract

Pulmonary arterial hypertension (PAH) is a fatal disease associated with severe remodeling of the large and small pulmonary arteries. Increased accumulation of inflammatory cells and apoptosis-resistant cells are contributing factors. Proliferative apoptosis-resistant cells expressing CD133 are increased in the circulation of PAH patients. Circulating cells can contribute to tissue repair via cell fusion and heterokaryon formation. We therefore hypothesized that in the presence of increased leukocytes and CD133-positive (CD133 pos ) cells in PAH lung tissue, cell fusion and resulting genomic instability could account for abnormal cell proliferation and the genesis of vascular lesions. We performed analyses of CD45/CD133 localization, cell fusion, and proliferation during late-stage PAH in human lung tissue from control subjects and subjects with idiopathic (IPAH) and familial (FPAH) PAH. Localization, proliferation, and quantitation of cell populations in individual patients were performed by immunolocalization. The occurrence of cellular fusion in vascular lesions was analyzed in lung tissue by fluorescence in situ hybridization. We found the accumulation of CD45 pos leukocytic cells in the tissue parenchyma and perivascular regions in PAH patients and less frequently observed myeloid cells (CD45/CD11b). CD133 pos cells were detected in occlusive lesions and perivascular areas in those with PAH and were more numerous in those with IPAH lesions than in FPAH lesions. Cells coexpressing CD133 and smooth muscle ␣-actin were occasionally observed in occlusive lesions and perivascular areas. Proliferating cells were more prominent in IPAH lesions and colocalized with CD45 or CD133. We found no evidence of increased ploidy to suggest cell fusion. Taken together, these data suggest that abnormal lesion formation in PAH occurs in the absence of cell fusion. vascular remodeling; chromosomal aneusomy; chimerism; cell fusion PULMONARY ARTERIAL HYPERTENSION (PAH) is often characterized by progressive pulmonary vascular remodeling, a process that contributes to increased pulmonary vascular resistance and ultimately right ventricular failure (24, 40). The vascular remodeling includes intimal thickening and fibrosis, medial hypertrophy, and often adventitial fibroproliferative changes that can be observed at many points along the longitudinal axis of the pulmonary circulation (10,32,38,45). The mechanisms contributing to the remodeling are complex and may vary depending on the specific vascular compartment or lesion and the potential stimuli involved in initiating or perpetuating the remodeling (8,24,29,32,38,45,58). However, it is increasingly appreciated that recruitment of inflammatory cells to the pulmonary artery wall occurs in the setting of PAH and that these cells likely play a pathogenic role in the remodeling process observed (18,24,32,46,50,54). Despite this observation, a systemic analysis of cell accumulation in the remodeled vessels of idiopathic (IPAH) or familial (FPAH) PAH has not been performed.

Evidence of Dysfunction of Endothelial Progenitors in Pulmonary Arterial Hypertension

“…Despite this, and despite previous work to the contrary (3,26,34), we found little evidence of ongoing proliferation in the plexiform lesions studied. This is in agreement with more recent work looking at proliferation in end-stage tissue (24). This lack of markers of proliferation may be a reflection of the end-stage nature of the tissue obtained from patients undergoing heart-lung transplantation and resident stem cells remain an attractive candidate.…”

“…Progenitor expansion would fit this oligoclonal model of lesion generation. Work looking at cell fusion in PAH tissue has demonstrated increased CD133-staining cells in IPAH and familial PAH plexiform lesions (24). We confirm this finding and demonstrate staining for c-Kit and CXCR4, both of which are associated with the progenitor phenotype.…”

“…In addition, confocal immunofluorescence demonstrated colocalization of c-Kit, the receptor for the cytokine stem cell factor, and therefore highly expressed on hematopoietic stem and progenitor cells (23) with CD31 ( Figures 2C, 2F, and 2I). There were isolated cells staining positive in the interstitium as previously reported by Majka and colleagues (24). Endothelial cell expression of the chemokine homing signal SDF-1 was up-regulated in plexiform lesions ( Figures 3F and 3H).…”

Glucose-6-phosphate dehydrogenase plays a critical role in hypoxia-induced CD133+progenitor cells self-renewal and stimulates their accumulation in the lungs of pulmonary hypertensive rats

“…They play a role in tissue genesis during gestation (35) and in the angiogenesis that promotes wound healing (4). CD133ϩ and bone marrow-derived stem cells also contribute to tumorigenesis (39,47,54) and pathogenic remodeling that reduces conductance in coronary (49) and pulmonary arteries (13,28,48,51), thereby contributing to chronic hypoxiainduced pulmonary hypertension (23,41). In response to hypoxia, circulating bone marrow-derived CD34 ϩ /CD133 ϩ /Flk ϩ and c-kit ϩ cells are recruited to the adventitial, medial or intimal compartments, where they assume mesenchymal or smooth muscle cell-like characteristics (29,38,43).…”

Fibrocytes: potential new therapeutic targets for pulmonary hypertension?

“…Intimal thickening and fibrosis, medial hypertrophy and fibroproliferative changes in the adventitia are common [3]. Virtually all of these changes are characterised, to a greater or lesser degree, by increased numbers of cells expressing smooth muscle aactin (a-SMA), as well as the accumulation of inflammatory cells [4][5][6][7]. At present, neither the origin of the accumulating cells, particularly those expressing a-SMA, nor the molecular mechanisms operating to cause their accumulation has been fully delineated.…”