Pulmonary fibrosis is characterized by fibroblast proliferation and extracellular matrix remodelling, leading to respiratory insufficiency. The mechanisms underlying this progressive and devastating disease remain unclear. Conditions that can impair the function of the endoplasmic reticulum (ER) cause accumulation of unfolded or misfolded proteins, resulting in ER stress and activation of the unfolded protein response (UPR). ER stress has been implicated in many conditions including cancer, diabetes, obesity, and inflammation. It is also involved in lung fibrosis, through myofibroblastic differentiation of fibroblasts; however, the precise role of ER stress in lung fibrosis is unknown. The current study aimed to investigate the underlying mechanisms of ER stress inhibitors in the treatment of bleomycin-induced lung fibrosis. We demonstrated that bleomycin can activate ER stress associated proteins, including GRP78, CHOP, and ATF-4, both in vitro and in vivo. PI3K/AKT acts upstream of ER stress to affect lung fibroblast proliferation, resulting in bleomycin-induced pulmonary fibrosis. Treatment with ER stress inhibitors or a PI3K inhibitor caused a reduction in fibroblast proliferation and improved pulmonary function. The relationship between PI3K/AKT/mTOR and ER stress in pulmonary fibrosis, and the application of PI3K inhibitors and ER stress inhibitors in the treatment of pulmonary fibrosis require further investigation.

Lineage commitment and tumorigenesis, traits distinguishing stem cells, have not been well characterized and compared in mesenchymal stem cells derived from human dental pulp (DP-MSCs) and bone marrow (BM-MSCs). Here, we report DP-MSCs exhibit increased osteogenic potential, possess decreased adipogenic potential, form dentin pulp-like complexes, and are resistant to oncogenic transformation when compared to BM-MSCs. Genome-wide RNA-seq and differential expression analysis reveal differences in adipocyte and osteoblast differentiation pathways, bone marrow neoplasm pathway, and PTEN/PI3K/AKT pathway. Higher PTEN expression in DP-MSCs than in BM-MSCs is responsible for the lineage commitment and tumorigenesis differences in both cells. Additionally, the PTEN promoter in BM-MSCs exhibits higher DNA methylation levels and repressive mark H3K9Me2 enrichment when compared to DP-MSCs, which is mediated by increased DNMT3B and G9a expression, respectively. The study demonstrates how several epigenetic factors broadly affect lineage commitment and tumorigenesis, which should be considered when developing therapeutic uses of stem cells.

The immunomodulatory effects of mesenchymal stem cells (MSCs) are established. However, the effects of MSCs on neutrophil survival in acute lung injury (ALI) remain unclear. The goal of this study was to investigate the effect of an MSC-conditioned medium (MSC-CM) on neutrophil apoptosis in endotoxin-induced ALI. In this study, an MSC-CM was delivered via tail vein injection to wild-type male C57BL/6 mice 4 h after an intratracheal injection of lipopolysaccharide (LPS). Twenty-four hours later, bronchoalveolar lavage fluid (BALF) and lung tissue were collected to perform histology, immunohistochemistry, apoptosis assay of neutrophil, enzyme-linked immunosorbent assays, and an electrophoretic mobility shift assay. Human neutrophils were also collected from patients with sepsis-induced acute respiratory distress syndrome (ARDS). Human neutrophils were treated in vitro with LPS, with or without subsequent MSC-CM co-treatment, and were then analyzed. Administration of the MSC-CM resulted in a significant attenuation of histopathological changes, the levels of interleukin-6 and macrophage inflammatory protein 2, and neutrophil accumulation in mouse lung tissues of LPS-induced ALI. Additionally, MSC-CM therapy enhanced the apoptosis of BALF neutrophils and reduced the expression of the anti-apoptotic molecules, Bcl-xL and Mcl-1, both in vivo and in vitro experiments. Furthermore, phosphorylated and total levels of nuclear factor (NF)-κB p65 were reduced in lung tissues from LPS + MSC-CM mice. Human MSC-CM also reduced the activity levels of NF-κB and matrix metalloproteinase-9 in the human neutrophils from ARDS patients. Thus, the results of this study suggest that the MSC-CM attenuated LPS-induced ALI by inducing neutrophil apoptosis, associated with inhibition of the NF-κB pathway.

Mesenchymal stem cell (MSC)-based therapies may aid in the repair of articular cartilage defects. The purpose of this study was to investigate the effects of intraarticular injection of allogeneic MSCs in an in vivo anterior cruciate ligament transection (ACLT) model of osteoarthritis in rabbits. Allogeneic bone marrow-derived MSCs were isolated and cultured under hypoxia (1% O₂). After 8 weeks following ACLT, MSCs suspended in hyaluronic acid (HA) were injected into the knees, and the contralateral knees were injected with HA alone. Additional controls consisted of a sham operation group as well as an untreated osteoarthritis group. The tissues were analyzed by macroscopic examination as well as histologic and immunohistochemical methods at 6 and 12 weeks post-transplantation. At 6 and 12 weeks, the joint surface showed less cartilage loss and surface abrasion after MSC injection as compared to the tissues receiving HA injection alone. Significantly better histological scores and cartilage content were observed with the MSC transplantation. Furthermore, engraftment of allogenic MSCs were evident in surface cartilage. Thus, injection of the allogeneic MSCs reduced the progression of osteoarthritis in vivo.

Collagen XVII/laminin-5 activates epithelial-to-mesenchymal transition and is associated with poor prognosis in lung cancer

Ankylosing spondylitis (AS) is a type of axial inflammation. Over time, some patients develop spinal ankylosis and permanent disability; however, current treatment strategies cannot arrest syndesmophyte formation completely. Here, we used mesenchymal stem cells (MSCs) from AS patients (AS MSCs) within the enthesis involved in spinal ankylosis to delineate that the HLA-B27–mediated spliced X-box–binding protein 1 (sXBP1)/retinoic acid receptor-β (RARB)/tissue-nonspecific alkaline phosphatase (TNAP) axis accelerated the mineralization of AS MSCs, which was independent of Runt-related transcription factor 2 (Runx2). An animal model mimicking AS pathological bony appositions was established by implantation of AS MSCs into the lumbar spine of NOD-SCID mice. We found that TNAP inhibitors, including levamisole and pamidronate, inhibited AS MSC mineralization in vitro and blocked bony appositions in vivo. Furthermore, we demonstrated that the serum bone-specific TNAP (BAP) level was a potential prognostic biomarker to predict AS patients with a high risk for radiographic progression. Our study highlights the importance of the HLA-B27–mediated activation of the sXBP1/RARB/TNAP axis in AS syndesmophyte pathogenesis and provides a new strategy for the diagnosis and prevention of radiographic progression of AS.