Fibrosis is a common disease process in which profibrotic cells disturb organ function by secreting disorganized extracellular matrix (ECM). Adipose tissue fibrosis occurs during obesity and is associated with metabolic dysfunction, but how profibrotic cells originate is still being elucidated. Here, we use a developmental model to investigate perivascular cells in white adipose tissue (WAT) and their potential to cause organ fibrosis. We show that a Nestin-Cre transgene targets perivascular cells (adventitial cells and pericyte-like cells) in WAT, and Nestin-GFP specifically labels pericyte-like cells. Activation of PDGFRα signaling in perivascular cells causes them to transition into ECM-synthesizing profibrotic cells. Before this transition occurs, PDGFRα signaling up-regulates mTOR signaling and ribosome biogenesis pathways and perturbs the expression of a network of epigenetically imprinted genes that have been implicated in cell growth and tissue homeostasis. Isolated Nestin-GFP+ cells differentiate into adipocytes ex vivo and form WAT when transplanted into recipient mice. However, PDGFRα signaling opposes adipogenesis and generates profibrotic cells instead, which leads to fibrotic WAT in transplant experiments. These results identify perivascular cells as fibro/adipogenic progenitors in WAT and show that PDGFRα targets progenitor cell plasticity as a profibrotic mechanism.

Mineralization is the most fundamental process in vertebrates. It is predominantly mediated by osteoblasts, which secrete mineral precursors, most likely through matrix vesicles (MVs). These vesicular structures are calcium and phosphate rich and contain organic material such as acidic proteins. However, it remains largely unknown how intracellular MVs are transported and secreted. Here, we use scanning electron-assisted dielectric microscopy and super-resolution microscopy for assessing live osteoblasts in mineralizing conditions at a nanolevel resolution. We found that the calcium-containing vesicles were multivesicular bodies containing MVs. They were transported via lysosome and secreted by exocytosis. Thus, we present proof that the lysosome transports amorphous calcium phosphate within mineralizing osteoblasts.

Fibroblast growth factor-2 (FGF-2) regulates a variety of functions of the periodontal ligament (PDL) cell, which is a key player during tissue regeneration following periodontal tissue breakdown by periodontal disease. In this study, we investigated the effects of FGF-2 on the cell migration and related signaling pathways of MPDL22, a mouse PDL cell clone. FGF-2 activated the migration of MPDL22 cells and phosphorylation of phosphatidylinositol 3-kinase (PI3K) and akt. The P13K inhibitors, Wortmannin and LY294002, suppressed both cell migration and akt activation in MPDL22, suggesting that the PI3K/akt pathway is involved in FGF-2-stimulated migration of MPDL22 cells. Moreover, in response to FGF-2, MPDL22 showed increased CD44 expression, avidity to hyaluronan (HA) partly via CD44, HA production and mRNA expression of HA synthase (Has)-1, 2, and 3. However, the distribution of HA molecular mass produced by MPDL22 was not altered by FGF-2 stimulation. Treatment of transwell membrane with HA facilitated the migration of MPDL22 cells and an anti-CD44 neutralizing antibody inhibited it. Interestingly, the expression of CD44 was colocalized with HA on the migrating cells when stimulated with FGF-2. Furthermore, an anti-CD44 antibody and small interfering RNA for CD44 significantly decreased the FGF-2-induced migration of MPDL22 cells. Taken together, PI3K/akt and CD44/HA signaling pathways are responsible for FGF-2-mediated cell motility of PDL cells, suggesting that FGF-2 accelerates periodontal regeneration by regulating the cellular functions including migration, proliferation and modulation of extracellular matrix production.

Fibrosis is the principal characteristic of the autoimmune disease known as scleroderma or systemic sclerosis (SSc). Studies published within the last three years suggest central involvement of platelet-derived growth factors (PDGFs) in SSc-associated fibrosis. PDGFs may also be involved in SSc-associated autoimmunity and vasculopathy. The PDGF signaling pathway is well understood and PDGF receptors are expressed on collagen-secreting fibroblasts and on mesenchymal stem and/or progenitor cells that may affect SSc in profound and unexpected ways. Although much work remains before we fully understand how PDGFs are involved in SSc, there is much interest in using PDGF inhibitors as a therapeutic approach to SSc.

Adipose tissue is an attractive source for somatic stem cell therapy. Currently, human adipose tissue-derived stromal cells/mesenchymal stem cells (hADSCs/MSCs) are cultured with fetal bovine serum (FBS). Recently, however, not only human embryonic stem cell lines cultured on mouse feeder cells but also bone marrow-derived human MSCs cultured with FBS were reported to express N-glycolylneuraminic acid (Neu5Gc) xenoantigen. Human serum contains high titers of natural preformed antibodies against Neu5Gc. We studied the presence of Neu5Gc on hADSCs/MSCs cultured with FBS and human immune response mediated by Neu5Gc. Our data indicated that hADSCs/MSCs cultured with FBS expressed Neu5Gc and that human natural preformed antibodies could bind to hADSCs/MSCs. However, hADSCs/MSCs express complement regulatory proteins such as CD46, CD55, and CD59 and are largely resistant to complement-mediated cytotoxicity. hADSCs/MSCs cultured with FBS could be injured by antibody-dependent cell-mediated cytotoxicity mechanism. Further, human monocyte-derived macrophages could phagocytose hADSCs/MSCs cultured with FBS and this phagocytic activity was increased in the presence of human serum. Culturing hADSCs/MSCs with heat-inactivated human serum for a week could markedly reduce Neu5Gc on hADSCs/MSCs and prevent immune responses mediated by Neu5Gc, such as binding of human natural preformed antibodies, antibody-dependent cell-mediated cytotoxicity, and phagocytosis. Adipogenic and osteogenic differentiation potentials of hADSCs/MSCs cultured with heat-inactivated human serum were not less than that of those cultured with FBS. For stem cell therapies based on hADSCs/MSCs, hADSCs/MSCs that presented Neu5Gc on their cell surfaces after exposure to FBS should be cleaned up to be rescued from xenogeneic rejection.