IL-3 Decreases Cartilage Degeneration by Downregulating Matrix Metalloproteinases and Reduces Joint Destruction in Osteoarthritic Mice.

Osteoarthritis (OA) is a chronic disease of articular joints that leads to degeneration of both cartilage and subchondral bone. These degenerative changes are further aggravated by proinflammatory cytokines including IL-1ß and TNF-α. Previously, we have reported that IL-3, a cytokine secreted by activated T cells, protects cartilage and bone damage in murine models of inflammatory and rheumatoid arthritis. However, how IL-3 protects cartilage degeneration is not yet known. In this study, we investigated the role of IL-3 on cartilage degeneration under both in vitro and in vivo conditions. We found that both mouse and human chondrocytes show strong expression of IL-3R at gene and protein levels. IL-3 increases the expression of mouse chondrocyte-specific genes, Sox9 and collagen type IIa, which were downregulated by IL-1ß. Moreover, IL-3 downregulated IL-1ß- and TNF-α-induced expression of matrix metalloproteinases in both mouse and human chondrocytes. Interestingly, IL-3 reduces the degeneration of articular cartilage and subchondral bone microarchitecture in a mouse model of human OA. Moreover, IL-3 showed the preventive and therapeutic effects on cartilage degeneration induced by IL-1ß in micromass pellet cultures of human mesenchymal stem cells. Thus, to our knowledge, we provide the first evidence that IL-3 has therapeutic potential in amelioration of degeneration of articular cartilage and subchondral bone microarchitecture associated with OA.

Adipose-Derived Mesenchymal Stem Cells Prevent Systemic Bone Loss in Collagen-Induced Arthritis.

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammatory synovitis leading to joint destruction and systemic bone loss. The inflammation-induced bone loss is mediated by increased osteoclast formation and function. Current antirheumatic therapies primarily target suppression of inflammatory cascade with limited or no success in controlling progression of bone destruction. Mesenchymal stem cells (MSCs) by virtue of their tissue repair and immunomodulatory properties have shown promising results in various autoimmune and degenerative diseases. However, the role of MSCs in prevention of bone destruction in RA is not yet understood. In this study, we investigated the effect of adipose-derived MSCs (ASCs) on in vitro formation of bone-resorbing osteoclasts and pathological bone loss in the mouse collagen-induced arthritis (CIA) model of RA. We observed that ASCs significantly inhibited receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis in both a contact-dependent and -independent manner. Additionally, ASCs inhibited RANKL-induced osteoclastogenesis in the presence of proinflammatory cytokines such as TNF-α, IL-17, and IL-1ß. Furthermore, treatment with ASCs at the onset of CIA significantly reduced clinical symptoms and joint pathology. Interestingly, ASCs protected periarticular and systemic bone loss in CIA mice by maintaining trabecular bone structure. We further observed that treatment with ASCs reduced osteoclast precursors in bone marrow, resulting in decreased osteoclastogenesis. Moreover, ASCs suppressed autoimmune T cell responses and increased the percentages of peripheral regulatory T and B cells. Thus, we provide strong evidence that ASCs ameliorate inflammation-induced systemic bone loss in CIA mice by reducing osteoclast precursors and promoting immune tolerance.

IL-3 inhibits human osteoclastogenesis and bone resorption through downregulation of c-Fms and diverts the cells to dendritic cell lineage.

IL-3 is an important cytokine that regulates hematopoiesis and functions as a link between the immune and the hematopoietic system. In this study, we investigated the role and mechanism of IL-3 action on human osteoclast formation and bone resorption using PBMCs. PBMCs differentiate into functional osteoclasts in the presence of M-CSF and receptor activator of NF-kappaB ligand as evaluated by 23c6 expression and bone resorption. We found that IL-3 dose-dependently inhibited formation of 23c6-positive osteoclasts, bone resorption and C-terminal telopeptide of type I collagen, a collagen degradation product. The inhibitory effect of IL-3 on bone resorption was irreversible. To investigate the mechanism of IL-3 action, we analyzed the effect of IL-3 on the receptor activator of NF-kappaB and c-Fms receptors and c-Fos, PU.1, NFAT cytoplasmic 1, and RelB transcription factors essential for osteoclastogenesis. IL-3 significantly inhibited c-Fms and downregulated both PU.1 and c-Fos at both mRNA and protein level. Furthermore, IL-3-treated cells showed increased expression of dendritic cell markers CD1a and CD80 and decreased expression of monocyte/macrophage marker CD14. Interestingly, IL-3 inhibited formation of human osteoclasts derived from blood monocytes and bone marrow cells of osteoporotic individuals. Thus, IL-3 may have therapeutic potential as an antiosteolytic agent in treatment of osteoporosis.