Objective To construct a model of knee osteoarthritis(KOA)through the co-culture of dorsal root ganglia(DRG)and fibroblast-like synoviocytes(FLSs).To investigate the effects of transient receptor potential vanilloid type 1(TRPV1)desensitization of sensory neurons induced by mechanical stimulation,including the alleviation of the FLSs inflammatory response.Methods DRG neuronal cells were identified through immunofluorescence.The stress loading of DRG neurons was realized using the FX-6000T cell stress system,and the effect of mechanical strain on the activity of DRG neurons was measured using the CCK-8 method.Ca2+ion flux in DRG neurons was studied through flow cytometry.A Transwell chamber and FLSs were used to establish a co-culture system.The contents of the pro-inflammatory factors IL-1β,TNF-α,and TGF-β in the supernatant were determined by ELISA.Gene and protein expression levels of TRPV1 and its desensitizing negative regulatory proteins PP2B,CaM,IL-1β,TNF-α,TGF-β,and α-SMA in DRG neurons were evaluated using RT-qPCR and Western blot,respectively.Results The Ca2+ion flux in DRG neurons increased under inflammatory conditions,and low intensity(sinusoidal,2％,1 Hz,6 h)thumb-pressing-induced mechanical stimulation did not alter Ca2+ion flux(P＞0.05).However,middle intensity(sinusoidal,4％,1 Hz,6 h)and high intensity(sinusoidal,8％,1 Hz,6 h)stimulation increased Ca2+ion flux significantly(P＜0.05).Notably,high intensity stimulation did not lead to a further increase in Ca2+ion flux over that for middle intensity stimulation(P＞0.05).There was no significant effect of low intensity stimulation on TRPV1,PP2B,or CaM gene or protein expression in DRG neurones,on IL-1β,TNF-α,or TGF-βconcentrations in the supernatant of co-cultured cells,or on IL-1β,TNF-α,TGF-β,or α-SMA gene or protein expression in FLSs(P＞0.05).Middle and high intensity mechanical stimulation up-regulated TRPV1 at the gene and protein expression levels in DRG neurons in the inflammatory group(P＜0.05)but down-regulated PP2B and CaM at the gene and protein expression levels(P＜0.05).Middle and high intensity mechanical stimulation decreased IL-1β,TNF-α,and TGF-β levels in the supernatants of co-cultured cells(P＜0.05)and decreased the gene and protein expression levels of IL-1β,TNF-α,TGF-β,and α-SMA in FLSs(P＜0.05).Conclusions Middle and high intensity thumb-pressing-induced mechanical stimulation induced TRPV1 desensitization of rat sensory neurons,reduced the release of pain mediators,and suppressed the FLSs inflammatory response through downregulating IL-1β,TNF-α,and TGF-β.

Objective To construct a model of knee osteoarthritis(KOA)through the co-culture of dorsal root ganglia(DRG)and fibroblast-like synoviocytes(FLSs).To investigate the effects of transient receptor potential vanilloid type 1(TRPV1)desensitization of sensory neurons induced by mechanical stimulation,including the alleviation of the FLSs inflammatory response.Methods DRG neuronal cells were identified through immunofluorescence.The stress loading of DRG neurons was realized using the FX-6000T cell stress system,and the effect of mechanical strain on the activity of DRG neurons was measured using the CCK-8 method.Ca2+ion flux in DRG neurons was studied through flow cytometry.A Transwell chamber and FLSs were used to establish a co-culture system.The contents of the pro-inflammatory factors IL-1β,TNF-α,and TGF-β in the supernatant were determined by ELISA.Gene and protein expression levels of TRPV1 and its desensitizing negative regulatory proteins PP2B,CaM,IL-1β,TNF-α,TGF-β,and α-SMA in DRG neurons were evaluated using RT-qPCR and Western blot,respectively.Results The Ca2+ion flux in DRG neurons increased under inflammatory conditions,and low intensity(sinusoidal,2％,1 Hz,6 h)thumb-pressing-induced mechanical stimulation did not alter Ca2+ion flux(P＞0.05).However,middle intensity(sinusoidal,4％,1 Hz,6 h)and high intensity(sinusoidal,8％,1 Hz,6 h)stimulation increased Ca2+ion flux significantly(P＜0.05).Notably,high intensity stimulation did not lead to a further increase in Ca2+ion flux over that for middle intensity stimulation(P＞0.05).There was no significant effect of low intensity stimulation on TRPV1,PP2B,or CaM gene or protein expression in DRG neurones,on IL-1β,TNF-α,or TGF-βconcentrations in the supernatant of co-cultured cells,or on IL-1β,TNF-α,TGF-β,or α-SMA gene or protein expression in FLSs(P＞0.05).Middle and high intensity mechanical stimulation up-regulated TRPV1 at the gene and protein expression levels in DRG neurons in the inflammatory group(P＜0.05)but down-regulated PP2B and CaM at the gene and protein expression levels(P＜0.05).Middle and high intensity mechanical stimulation decreased IL-1β,TNF-α,and TGF-β levels in the supernatants of co-cultured cells(P＜0.05)and decreased the gene and protein expression levels of IL-1β,TNF-α,TGF-β,and α-SMA in FLSs(P＜0.05).Conclusions Middle and high intensity thumb-pressing-induced mechanical stimulation induced TRPV1 desensitization of rat sensory neurons,reduced the release of pain mediators,and suppressed the FLSs inflammatory response through downregulating IL-1β,TNF-α,and TGF-β.