Intracellular calcium signaling of chondrocytes and the treatment of osteoarthritis

Lu, X. LucasChondrocyte, the sole cell population in articular cartilage, is responsible for the homeostasis of the extracellular matrix in cartilage. My thesis work aimed to understand the metabolism of cartilage, chondrocyte, and their mutual interactions, with the purpose for the search of potential treatments for osteoarthritis (OA). To study the behaviors of chondrocytes residing in their native environment, long-term in vitro culture of cartilage explants were investigated. In my first study, the effects of serum medium and serum-free chondrogenic medium for cartilage explant culture were compared. To evaluate the behaviors of in situ chondrocytes in the two culture medium, an in situ imaging approach was developed, where the spontaneous intracellular calcium ([Ca2+]i) signaling of chondrocytes could be recorded and analyzed. We proved that the serum-free chondrogenic medium is beneficial for the mechanical integrity of cartilage tissue, as well as the viability, phenotype, and metabolic activities of chondrocytes. Aging is strongly correlated with the occurrence of OA. To understand the effect of age on chondrocyte metabolism, my second study was to analyze the correlation between aging and [Ca2+]i signaling of chondrocyte, as well as the impact of osmotic environment. We found that adult chondrocytes have more vigorous [Ca2+]i signaling than juvenile chondrocytes. In this thesis, the spontaneous [Ca2+]i signaling is employed as an important indicator of chondrocyte metabolic behaviors. Thus my third study serves as a systematic effort to understand the features and potential initiation mechanisms of the spontaneous [Ca2+]i signaling of chondrocyte. A theoretical biophysical model was built to describe the spontaneous [Ca2+]i peaks, The model can successfully explain the lognormal distribution of signaling-related temporal parameters and the “fingerprint” phenomenon. Using eight pathway antagonists, it was found that the initiation of spontaneous [Ca2+]i peaks in chondrocytes requires extracellular Ca2+ source. PLC-IP3 pathway, purinoceptors, and TRPV4 channel on plasma membrane also play key roles in the spontaneous [Ca2+]i signaling of chondrocytes. My last study was targeting at a potential molecule for OA treatment, i.e., investigating the chondro-protective effects of resveratrol. Resveratrol is a natural polyphenol known for its anti-oxidation effects. My study revealed the protective effects of resveratrol on chondrocytes under inflammatory attack. A novel collagen association effect of resveratrol was discovered, where the resveratrol molecules are able to associate collagen fibrils via the dynamic hydrogen bonds. This is particularly important for future treamtment of OA, especially for the middle stage OA where the number of functional chondrocytes are highly limited in the degenerated cartilage. Taken together, studies in this thesis contribute to the further understanding of the in vitro behaviors of cartilage, spontaneous [Ca2+]i signaling of chondrocytes, and the chondro-protective mechanisms of resveratrol, all of which are to serve the potential treatment of OA.University of Delaware, Department of Mechanical EngineeringPh.D