Mesenchymal stem cells produce Wnt isoforms and TGF-β₁ that mediate proliferation and procollagen expression by lung fibroblasts

Abstract

Studies have been carried out previously to determine whether mesenchymal stem cells (MSC) influence the progression of pulmonary fibrosis. Here, we asked whether MSC (derived from mouse bone marrow and human umbilical cord blood) produce factors that mediate lung fibroblast (LF) growth and matrix production. MSC-conditioned media (CM) were found by ELISA to contain significant amounts of PDGF-AA and transforming growth factor-beta1 (TGF-beta1). Proliferation was increased in a concentration-dependent manner in LF cell lines and primary cells cultured in MSC-CM, but neither anti-PDGF antibodies nor PDGF receptor-specific antibodies affected proliferation, nor did a number of other antibodies to well-known mitogenic factors. However, proliferation was significantly inhibited by the Wnt signaling antagonist, secreted frizzled related protein-1 (sFRP-1). In addition, anti-Wnt1 and anti-Wnt2 antibodies attenuated MSC-CM-induced proliferation, and increased expression of Wnt7b was identified. As would be expected in cells activated by Wnt, nuclear beta-catenin was increased. The amount of TGF-beta1 in MSC-CM and its biological activity were revealed by activation at acidic pH. The stem cells synthesized and released TGF-beta1 that increased alpha1-procollagen gene expression by LF target cells. Addition of anti-TGF-beta to the MSC-CM blocked upregulation of collagen gene expression. These data demonstrate that MSC from mice and humans produce Wnt proteins and TGF-beta1 that respectively stimulate LF proliferation and matrix production, two hallmarks of fibroproliferative lung disease. It will be essential to determine whether these factors can play a role in attempts to use MSC for therapeutic approaches.

Therapeutic Potential of Umbilical Cord Mesenchymal Stem Cells for Inhibiting Myofibroblastic Differentiation of Irradiated Human Lung Fibroblasts

“…The associations between the Wnt pathway and MSCs (Salazar et al 2009) were further examined in the present study. We found that irradiation of nHLFs enhanced Wnt signaling, consistent with earlier reports (Gurung et al 2009).…”

“…For this reason, co-culture systems have been used widely to investigate the effects of MSCs on other cell types. Although there is evidence that co-culture with MSCs promotes fibroblast proliferation (Kim et al 2007;Salazar et al 2009), information is lacking concerning the effects of MSCs on irradiated lung fibroblasts. Here, we found that co-culture with HUMSCs attenuated the radiation-induced up-regulation of α-SMA in nHLFs.…”

“…MSCs have also been implicated in Wnt signaling. Salazar et al (2009) observed that the CM of MSCs contained Wnt proteins that were capable of stimulating lung fibroblast proliferation through activation of the canonical Wnt/β-catenin signaling pathway. Another group have reported that canonical Wnt signaling is activated in nHLFs following irradiation, and that β-catenin mediates the effects of ionizing radiation on fibroblasts, acting to decrease the severity of radiation-induced soft tissue complications (Gurung et al 2009).…”

“…Thus, transplanting MSCs may represent a promising strategy for limiting the progression of fibrosis, although more research is needed to understand the underlying mechanisms. Several studies have implicated the canonical Wnt/β-catenin signaling in fibroblast differentiation (Salazar et al 2009), raising the possibility that this pathway may be involved in the anti-fibrotic actions of MSCs. In the present study, we test this possibility by examining the effects of human umbilical cord MSCs (HUMSCs) on radiation-induced Wnt/β-catenin signaling in HLFs, and on the differentiation of HLFs into myofibroblasts.…”

Resident Tissue-Specific Mesenchymal Progenitor Cells Contribute to Fibrogenesis in Human Lung Allografts

“…16,36 However, MSCs potentiate fibrotic differentiation of other mesenchymal cells by secreting profibrotic mediators, such as TGF-␤1. 37 Thus, although MSCs can likely modulate an inflammatory microenvironment, they can also promote fibrogenesis by secreting profibrotic mediators 37 or differentiating to myofibroblasts. Regulation of native LR-MSC synthetic function and fibrotic differentiation fate by the local milieu might play a central role in dictating whether these cells serve a predominant immunoregulatory function or promote fibroproliferative events that favor the development of BO.…”