Induction of CD44 cleavage in articular chondrocytes

Askew

Journal of Biological Chemistry

et al. 2016

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Depletion of the cartilage proteoglycan aggrecan is one of the earliest events that occurs in association with osteoarthritis. This loss is often accompanied by a coordinate loss in another glycosaminoglycan, hyaluronan. Chondrocytes experimentally depleted of cell-associated hyaluronan respond by switching to a pro-catabolic metabolism that includes enhanced production of endogenous inflammatory mediators and increased synthesis of matrix metalloproteinases. Hyaluronan turnover is also increased. Together, such a response provides for possible establishment of a self-perpetuating spiral of events that maintains or prolongs the pro-catabolic state. Chondrocytes or cartilage can also be activated by treatment with pro-inflammatory cytokines and mediators such as IL-1␤, TNF␣, LPS, fibronectin fragments, and hyaluronan oligosaccharides. To determine the mechanism of chondrocyte activation due to hyaluronan loss, a depletion method was required that did not include degrading the hyaluronan. In recent years, several laboratories have used the coumarin derivative, 4-methylumbelliferone, as a potent inhibitor of hyaluronan biosynthesis, due in part to its ability to sequester intracellular UDP-glucuronic acid and inhibition of hyaluronan synthase transcription. However, contrary to our expectation, although 4-methylumbelliferone was indeed an inhibitor of hyaluronan biosynthesis, this depletion did not give rise to an activation of chondrocytes or cartilage. Rather, 4-methylumbelliferone directly and selectively blocked gene products associated with the pro-catabolic metabolic state of chondrocytes and did so through a mechanism preceding and independent of hyaluronan inhibition. These data suggest that 4-methylumbelliferone has additional useful applications to block pro-inflammatory cell activation events but complicates how it is used for defining functions related to hyaluronan.The pronounced loss of aggrecan from articular cartilage is an early critical event associated with osteoarthritis (OA) 2 (1, 2). Aggrecan turnover within the extracellular matrix occurs due to the enhanced activity of endoproteinases such as a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) 4 (3, 4) and 5 (5, 6) as well as other matrix metalloproteinases (MMPs) (7)(8)(9)(10)(11). In addition to aggrecan, a significant loss of hyaluronan (HA) is also observed in human OA cartilage as compared with normal human cartilage (12,13). A marked depletion of HA was also observed in articular cartilage damaged experimentally, such as in the anterior cruciate ligament transection model of OA (14) and a reduced-loading, splint immobilization model (15) in dogs. In our studies, cultured explants of human articular cartilage treated with IL-1␣ displayed a loss of HA within the superficial and upper middle layers of cartilage, the same layers in which aggrecan loss occurred (16). Other studies on cytokine-stimulated cartilage explants suggested that HA is lost from the cartilage (17,18), and other studies revealed that the HA is lost...

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: -Mu Inhibition Of Mmp Production Independent Of Ha Blockmentioning

confidence: 99%

See 3 more Smart Citations

4-Methylumbelliferone Diminishes Catabolically Activated Articular Chondrocytes and Cartilage Explants via a Mechanism Independent of Hyaluronan Inhibition

Askew

Journal of Biological Chemistry

et al. 2016

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Arthritis & Rheumatology

CD44 and Hyaluronan Promote the Bone Morphogenetic Protein 7 Signaling Response in Murine Chondrocytes

Luo

Knudson

Askew

et al. 2014

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Objective Cell–matrix interactions promote cartilage homeostasis. We previously found that Smad1, the transcriptional modulator of the canonical bone morphogenetic protein 7 (BMP-7) pathway, interacted with the cytoplasmic domain of CD44, the principal hyaluronan receptor on chondrocytes. To elucidate the physiologic function of CD44–Smad1 interactions, as well as the role of hyaluronan, we studied the response of chondrocytes isolated from CD44−/− and BALB/c (wild-type [WT]) mice to stimulation with BMP-7. Methods In primary murine chondrocytes, CD44 expression was decreased by small interfering RNA (siRNA) transfection or was enhanced by plasmid transfection. Pericellular hyaluronan was removed by hyaluronidase treatment, or its endogenous synthesis was inhibited. Changes in response to BMP-7 stimulation were evaluated by Western blotting of Smad1 phosphorylation and aggrecan messenger RNA (mRNA) expression. Results Chondrocytes from CD44−/− mice and WT mice transfected with CD44 siRNA were less responsive than untransfected chondrocytes from WT mice to BMP-7. CD44−/− mouse chondrocytes transfected with pCD44 showed increased sensitivity to BMP-7. Significant increases in aggrecan mRNA were observed in WT mouse chondrocytes in response to 10 ng/ml of BMP-7, whereas at least 100 ng/ml of BMP-7 was required for CD44−/− mouse chondrocytes. However, in chondrocytes from CD44−/− and WT mice, hyaluronidase treatment decreased cellular responses to BMP-7. Treatment of both bovine and murine chondrocytes with 4-methylumbelliferone to reduce the synthesis of endogenous hyaluronan confirmed that hyaluronan promoted BMP-7 signaling. Conclusion Taken together, these investigations into the mechanisms underlying BMP-7 signaling in chondrocytes revealed that while hyaluronan-dependent pericellular matrix is critical for BMP-7 signaling, the expression of CD44 promotes the cellular response to lower concentrations of BMP-7.

Suppression of murine osteoarthritis by 4‐methylumbelliferone

Tsuchiya

Ōhashi

Journal Orthopaedic Research

et al. 2019

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Using in vitro models, we previously reported that 4-methylumbelliferone (4-MU) blocked many of the pro-catabolic features of activated chondrocytes. 4-MU also blocked safranin O loss from human cartilage explants exposed to interleukin 1β (IL1β) in vitro. However, the mechanism for this chondroprotective effect was independent of the action of 4-MU as a hyaluronan (HA) inhibitor. Interestingly, overexpression of HA synthase 2 (HAS2) also blocked the same pro-catabolic features of activated chondrocytes as 4-MU via a mechanism independent of extracellular HA accumulation. Data suggest that altering UDP-sugars may be behind these changes in chondrocyte metabolism. However, all of our previous experiments with 4-MU or HAS2 overexpression were performed in vitro. The purpose of this study was to confirm whether 4-MU was effective at limiting the effects of osteoarthritis (OA) on articular cartilage in vivo. The progression of OA was evaluated after destabilization of the medial meniscus (DMM) surgery on C57BL/6 mice in the presence or absence of 4-MU-containing chow. Mice fed 4-MU after DMM surgery exhibited significant suppression of OA starting from an early stage in vivo. Mice fed 4-MU exhibited lower OARSI scores after DMM; reduced osteophyte formation and reduced MMP3 and MMP13 immunostaining. 4-MU also exerted pronounced chondroprotective effects on murine joint cartilage exposed to IL1β in vitro and, blocked IL1β-enhanced lactate production in cartilage explants. Therefore, 4-MU is effective at significantly reducing the loss of proteoglycan and reducing MMP production both in vitro and in vivo as well as cartilage damage and osteophyte formation in vivo after DMM.