Poster CC5 - Exploring the Impact of Simulated Microgravity on Osteoarthritis Development: The Role of CD36 and Sex-Specific Responses in a Mouse Model

Introduction: Leveraging the unique conditions of space microgravity, our research explores osteoarthritis (OA), which affects over three million Canadians and commonly targets load-bearing joints like the knee. Notably, knee OA (KOA) shows a higher incidence and severity in females, a disparity not fully explained by conventional risk factors. Our studies use rotating wall vessel (RWV) technology to simulate spaceflight conditions on Earth, focusing on the biomechanical unloading that mimics microgravity. This approach helps us investigate potential mechanisms underlying OA's development and progression.
Initial findings show that simulated microgravity (SMG) significantly alters molecular expression in engineered meniscus constructs from non-KOA patients, affecting genes linked to chondrocyte hypertrophy and OA progression while downregulating protective genes. Sex-specific molecular responses to SMG also emerged, with distinct differences between male and female specimens, underscoring the importance of considering biological sex in OA research. Further, extended RNA sequencing under SMG conditions revealed sex-specific OA-like transcriptomic profiles, particularly in females.
A key discovery is the modulation of CD36, a transmembrane protein involved in lipid metabolism and OA pathogenesis, whose expression changes under SMG and is upregulated in KOA patients. This finding highlights how microgravity-induced cellular responses can provide insights into OA development, especially regarding sex-specific differences.

Materials and

Methods: In this phase of our investigation, we employed age-matched young mice, encompassing both sexes, including CD36 knockout (ko) mice and their C57Bl/6 strain control counterparts, as our animal model. Meniscus tissues were extracted from these mice, including both medial and lateral sections, leading to the creation of four distinct experimental groups: 1.Female CD36 ko mice 2.Female C57Bl/6 control mice 3.Male CD36 ko mice 4.Male C57Bl/6 control mice. These isolated meniscus tissues underwent a 3-week culture in simulated microgravity (SMG) conditions, utilizing a rotating wall vessel bioreactor. A control group was concurrently maintained under standard gravity conditions for comparative analysis.
Following the culture period, tissue constructs from each group were randomly selected for a series of analyses, including RNA sequencing (RNAseq) and reverse transcription-quantitative polymerase chain reaction (RT-qPCR), bone mineral quantification, histology and immunofluorescence assessments, shotgun proteomics, and evaluations of DNA and cartilaginous glycosaminoglycan (GAG) content (Figure1).

Results, Conclusions, and Discussions: The groups exposed to SMG, regardless of their genotype, showed significant degradation of extracellular matrix (ECM) components and a marked reduction in GAG content compared to the control group. These changes suggest an enhanced process of local hypertrophic differentiation and calcification, underscoring the potent OA-inducing effects of the SMG environment. Notably, within the SMG-exposed female cohorts, the deletion of CD36 significantly mitigated the advancement of meniscus calcification. By day 21, the calcification region in the CD36 ko group was approximately 20% smaller in size than that observed in the wild-type (WT) counterparts. Ongoing RNA sequencing aims to elucidate the specific mechanisms by which CD36 influences.
This investigation sheds light on the complex molecular interplay modulated by microgravity, enhancing our comprehension of OA's pathogenesis, particularly regarding sex-specific differences and the modulatory role of CD36. By simulating the conditions of spaceflight microgravity, our research unveils novel insights into the mechanisms driving KOA and delineates the protective function of CD36 within this context. The findings not only bridge a significant gap in our understanding of OA but also lay the groundwork for the development of innovative therapeutic strategies. The pivotal role of CD36 in OA progression under SMG conditions accentuates the potential for targeted interventions, both in space health management and terrestrial medical practice, opening new avenues for the prevention and treatment of OA.

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