Background/Purpose: Osteoarthrosis (OA) is a leading cause of pain, disability and early mortality, with no disease modifying treatments. Mitochondrial dysfunction is a known driver of disease. Mesenchymal stromal cells (MSCs) -widely tested in OA- transfer their mitochondria (MT) to damaged tissues in response to stress. Aim: To characterize the functional impact of MT transfer (MitoT) from umbilical cord-derived MSC (MSCs) to the human OA chondrocyte (OA-Ch) and clinical effect of MSC-derived MT in a murine model of OA.

Methods: Primary chondrocytes from OA patient surgery were tested for MitoT using in vitro co-culture with MSCs. MitoT was evidenced by flow cytometry and confocal microscopy of MitoTracker stained and YPF-tagged MT protein. To single out effects of MitoT on target cells, we employed direct transfer of MSC-derived MT to OA-Chs (Mitoception). The response of target cells was gauged by ATP production, oxygen consumption (OCR), extracellular acidification (ECAR) rates, levels of reactive oxygen species (ROS) superoxide dismutase (SOD), MT network fussion/fission and OA-Ch viability by TUNEL assays. Intra-articular injection of MSC-derived MT was tested in a collagenase induced murine model of OA.

Results: Dose-dependent cell-to-cell MitoT from MSCs to cultured OA-Chs was detected starting at 4 hours of co-culture, with increasing (3.2x) MT-fluorescence levels at higher MSC:Ch ratios. PCR analysis confirmed the presence of exogenous MSC-MT within MitoT⁺ OA-Chs up to 9 days post Mitoception. Metabolic analysis showed a 2x increase (p< 0.001) in ATP and a higher OXPHOS/Glycolysis ratio (p=0.0213) in target OA-Chs revealing a switch towards an activated energy state of chondrocytes after MitoT. Increased SOD2 mRNA transcripts (p< 0.05), protein levels (1.8-fold), MT-SOD activity (2.9-fold) and reduced ROS levels (p=0.039) were coincident with enhanced resistance of OA-Chs to apoptosis, indicating this effect of MitoT is related to the control of ROS. In parallel, the change in mRNA transcripts and proteins that control the fusion/fission state of the MT network, showed increased expression of MFN2 (p< 0.01) and decreased p-DRP1 (p< 0.05) that promote a predominantly fused MT network, that contributes to chondrocyte preservation. In the preclinical OA model, intra-articular treatment with MSC-derived MT improved histologic scores (p< 0.001) and MicroCT imaging of the diseased joints (p< 0.01).

Conclusion: MSC-derived MT transferred to the OA-Ch convey significant changes in energy balance, MT dynamics, resistance to oxidative stress and OA-Ch apoptosis. Intra-articular MT treatment improved disease in a murine model of OA. These findings might represent a new strategy in the treatment of this disease.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/mitochondrial-transfer-functionally-restores-the-human-osteoarthritis-oa-chondrocyte-is-protective-against-oxidative-stress-and-improves-oa-in-a-clinical-model-of-disease/