Activation of NOTCH1 by Shear Force Elicits Immediate Cytokine Expression in Human Chondrocytes.

Hao-Jen Cheng,Chin Li,Cheng-Nan Chen,Wan-Ting Hsu

doi:10.3390/ijms21144958

Abstract

Osteoarthritis is caused by overloading of joints and is characterized by inflammation-induced disruption of cartilage structure. Current treatment strategy aims to relieve inflammation and prevent further deterioration of joint function. However, how mechanical force leads to inflammation and deterioration of chondrocyte function still remains incompletely understood. To explore the force-regulated molecular mechanism, an in vitro hydraulic shear force experiment to simulate the condition of force loading was required. The result demonstrated that multiple cytokines and immune regulators, including interleukin 8, interferon β, TRAF1 and TNFAIP3, were significantly increased by shear force within two hours of treatment. Moreover, JAG1 and HES1 were drastically upregulated as well, suggesting that NOTCH1 signaling is activated by shear force. Short-term expression of NOTCH1 intracellular domain activated a similar set of cytokines, indicating that NOTCH1 responds to shear force and activates downstream genes. When incubated under the medium conditioned by NOTCH1-activated chondrocyte, osteoblasts expressed higher levels of interferon β and interferon λ. Together, our results indicated that NOTCH1 functions as a force sensor and promotes expression of cytokines and immune regulators from shear-force bearing chondrocytes.

Highlights

Osteoarthritis (OA) is the most common age-related joint disease, causing pain and swelling of joints [1]
The cells were removed from the hydraulic chamber and immediately lysed for RNA collection
Gene expression profiles before and after fluid shear force treatment was determined by RNA sequencing

Summary

Introduction

Osteoarthritis (OA) is the most common age-related joint disease, causing pain and swelling of joints [1]. The changes include the acquisition of a fibroblast-like morphology, decreases in type II collagen expression, and increases in type I collagen expression [10,11] This switch of matrix protein expression results in synovial fibrosis, causing joint stiffness and pain. The function of chondrocytes is subsequently altered and unable to compensate for the loss of matrix, resulting in a net loss of cartilage matrix These inflammatory cytokines include IL-6 and IL-8. Besides regulating matrix formation, NOTCH1 is able to sustain NFκB activation and is associated with increased expression of inflammatory cytokine from synoviocytes and chondrocytes [4,27], promoting the progression of OA. To explore the role of NOTCH1 in force-induced inflammatory response, we expressed the active form of NOTCH1 and found that NOTCH1 elevates the expression of IL-8 and TNFα, two cytokines promoting joint inflammation. Our data suggests that the NOTCH1 signaling acts as a sensor to relay mechanic pressure and induce expression of inflammatory cytokines in chondrocytes

Identification of Shear Stress Immediate Response Genes in Chondrocytes

Cell Culture and Treatment

RNA Sequencing

Availability of Supporting Data