Background/Purpose: Osteoarthritis (OA) is the most common joint disease and a leading cause of disability. Cartilage degeneration is the central characteristic of OA, and low-grade synovitis can promote OA progression. In OA, both chondrocytes and synoviocytes undergo metabolic alterations and shift from a resting regulatory state to a highly metabolically active state. Choline kinase (ChoK) is an enzyme that catalyzes the conversion of choline to phosphocholine, which serves as a precursor for the production of phosphatidylcholine (PtdCho). PtdCho is the major phospholipid constituent of membranes and substrate for the synthesis of lipid signaling molecules such as lysophosphatidic acid (LPA) and phosphatidic acid (PA). Here, we determined whether ChoK is a key regulator of OA synoviocytes and chondrocytes phenotype.

Methods: ChoK expression in OA synovial and cartilage tissues was evaluated by immunohistochemistry (IHC). Human fibroblast-like synoviocytes (FLS), mouse macrophages (tioglycollate-elicited), human knee chondrocytes, synovial and cartilage explants were stimulated with proinflammatory mediators (IL-1b (2ng/ml), TNFa (10ng/ml) and LPS (100ng/ml)) in the presence or absence of MN58b (5mM), an inhibitor of ChoKa. Release of IL-1β, IL-6 and MMP3 was quantified from conditioned media by ELISAs. Phosphorylation of AMPKain FLS and chondrocytes was examined by Western Blot analysis. Expression of fibrosis-related genes including collagen (COL) 1α1, COL2α1, COL10α1, αsmooth muscle actin (αSMA) and procollagen-lysin,2-oxoglutarate 5-dioxygenase 2 (PLOD2) was quantified in FLS treated with TGFb (10ng/ml) by quantitative RT-PCR.

Results: IHC studies demonstrated that ChoK expression was upregulated in human knee OA cartilage and synovium, and in normal cartilage with aging in situ. In addition, ChoK activity was increased in human OA FLS, and was significantly enhanced by inflammatory mediators in synoviocytes and chondrocytes. Moreover, pharmacological inhibition of ChoK activity by MN58b significantly decreased IL-1β-induced nitric oxide (NO) secretion from 8.3 ±4 μM to 0.72 ±0.3 μM (p = 0.0004, 3 donors) in OA chondrocytes, and MMP-13 release in chondrocytes and cartilage explants. At the same time, it attenuated IL-6 secretion from 31.4 ± 4.85 ng/ml to 26.6 ± 6.3 ng/ml (p = 0.02)in OA synovium explants. MN58b also impaired IL-1βsecretion in macrophages and synovium explants (from 0.46 ±0.09 ng/ml to 0.015 ±0.009 ng/ml; p = 2.64E-05, 3 donors) in response to LPS+ATP simulation. These were associated with increased phosphorylation of AMPKαin chondrocytes, FLS and in synovium explants. Furthermore, MN58b suppressed by >50% (p<0.05) the expression of fibrosis related genes, COL1α1, COL2α1, COL10α1,αSMA and PLOD2 in OA FLS in response to TGFβ1.

Conclusion: Dysregulation of ChoK is likely involved in OA pathogenesis, and ChoK could potentially be a novel target for OA. Further translational and mechanistic studies of pharmacologic inhibition of ChoK on OA progression are warranted.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-potential-role-of-choline-kinase-alpha-in-osteoarthritis/