Yu Matsukura

Mouse Synovial Mesenchymal Stem Cells Increase in yield with Knee Inflammation

Even though mouse studies have various advantages, harvesting an adequate number of synovial mesenchymal stem cells (MSCs) is difficult in mice. We investigated whether the total yield of MSCs increased in synovium with inflammation in mice. Infrapatellar fat pads (IFPs) were harvested from 10 knees of 5 mice 3, 7, and 14 days after intraarticular injection of carrageenan. Ten IFPs were also harvested from untreated knees as a control. Seven days after initial plating, the total yield of cells was compared among the 4 groups (n = 4–6). The harvested cells were analyzed for multipotentiality and surface epitopes. Furthermore, knee synovitis was compared among the 4 groups in histology. The number of cells in the 3 and 7 days treated group was significantly higher than the other groups. The harvested cells had characteristics of MSCs. Synovitis in the 3 and 7 days treated groups was significantly severer than the other groups. There seemed to be a relationship between the synovitis score and the total yield of cells derived from IFPs. In mice, it became possible to increase the yield 50‐fold by inducing inflammation. This method makes it possible to analyze the molecular mechanisms of cartilage regeneration of synovial MSCs in mice models.

Elimination of BMP7 from the developing limb mesenchyme leads to articular cartilage degeneration and synovial inflammation with increased age

While osteo‐ and chondro‐inductive activities of recombinant human bone morphogenetic protein 7 are well established, evaluation of the role of endogenous BMP7 in skeletal homeostasis has been hampered by perinatal lethality in BMP7 knockout mice. Here, we examined physiological roles of endogenous BMP7 in joint homeostasis and showed that proteoglycan contents in articular cartilage were significantly reduced in the absence of BMP7. Loss of BMP7 did not affect survival of articular cartilage cells, but resulted in reduced expression of aggrecan and enhanced expression of matrix metalloproteinase 13. We also found extensive synovial hyperplasia and enhanced expression of Activin A. These findings suggest that locally produced BMP7 is prerequisite for postnatal synovial joint homeostasis and may be involved in osteoarthritic changes in adults.

Human YKL39 (chitinase 3-like protein 2), an osteoarthritis-associated gene, enhances proliferation and type II collagen expression in ATDC5 cells

Human YKL39 (chitinase 3-like protein 2/CHI3L2) is a secreted 39kDa protein produced by articular chondrocytes and synoviocytes. Recent studies showed that hYKL-39 expression is increased in osteoarthritic articular chondrocytes suggesting the involvement of hYKL-39 in the progression of osteoarthritis (OA). However little is known regarding the molecular function of hYKL-39 in joint homeostasis. Sequence analyses indicated that hYKL-39 has significant identity with the human chitotorisidase family molecules, although it is considered that hYKL-39 has no enzymatic activity since it lacks putative chitinase catalytic motif. In this study, to examine the molecular function of hYKL-39 in chondrocytes, we overexpressed hYKL-39 in ATDC5 cells. Here we report that hYKL-39 enhances colony forming activity, cell proliferation, and type II collagen expression in these cells. These data suggest that hYKL-39 is a novel growth and differentiation factor involved in cartilage homeostasis.

Follistatin alleviates synovitis and articular cartilage degeneration induced by carrageenan.

Activins are proinflammatory cytokines which belong to the TGFβ superfamily. Follistatin is an extracellular decoy receptor for activins. Since both activins and follistatin are expressed in articular cartilage, we hypothesized that activin-follistatin signaling participates in the process of joint inflammation and cartilage degeneration. To test this hypothesis, we examined the effects of follistatin in a carrageenan-induced mouse arthritis model. Synovitis induced by intra-articular injection of carrageenan was significantly alleviated by preinjection with follistatin. Macrophage infiltration into the synovial membrane was significantly reduced in the presence of follistatin. In addition, follistatin inhibited proteoglycan erosion induced by carrageenan in articular cartilage. These data indicate that activin-follistatin signaling is involved in joint inflammation and cartilage homeostasis. Our data suggest that follistatin can be a new therapeutic target for inflammation-induced articular cartilage degeneration.

Hypoxia enhances proliferation through increase of colony formation rate with chondrogenic potential in primary synovial mesenchymal stem cells

Synovial mesenchymal stem cells (MSCs) are an attractive cell source for cartilage and meniscus regeneration. Use of primary MSCs is the preferable because these cells are safer than cells passaged several times in terms of probability of chromosome abnormalities. The effect of hypoxia on the proliferation of MSCs is controversial and remains unknown in primary synovial MSCs. Primary synovial MSCs were cultured at normoxia or hypoxia, and colony number, cell number, surface epitopes, mitochondria activity, TEM finding, and chondrogenic potential were analyzed. To investigate the effect of hypoxia on attachment of synovial MSCs, cells were cultured at hypoxia for the first 3 days, then cultured at normoxia. To investigate the effect of hypoxia on proliferation, cells were also cultured at hypoxia for the last 11 days. Hypoxia increased colony number and cell number per dish in primary synovial MSCs. Hypoxia did not affect cell number per colony, surface epitopes, mitochondria activity, TEM finding or chondrogenic potential. Hypoxia for the first 3 days did not alter colony number per dish or cell number per dish, while hypoxia for the last 11 days increased. Hypoxia enhanced proliferation through increase of colony formation rate with chondrogenic potential in primary synovial MSCs.