The loss of OPA1 accelerates intervertebral disc degeneration and osteoarthritis in aged mice.

Recent studies have highlighted the importance of mitochondria in NP cells and articular chondrocyte health. Since the understanding of mechanisms governing mitochondrial dynamics in these tissues is lacking, we investigated the role of OPA1, a mitochondrial fusion protein, in their homeostasis. OPA1 knockdown in NP cells altered mitochondrial size and cristae shape and increased the oxygen consumption rate. OPA1 governed the morphology of multiple organelles, including peroxisomes, early endosomes and cis-Golgi and loss resulted in the dysregulation of autophagy. Metabolic profiling and C-flux analyses revealed TCA cycle anaplerosis and altered metabolism in OPA1-deficient NP cells. Noteworthy, Opa1 mice showed age-dependent disc degeneration, osteoarthritis, and vertebral osteopenia. RNA-Sequencing of Opa1 NP tissue revealed dysregulation of metabolism, autophagy, cytoskeletal reorganization, and extracellular matrix and shared strong thematic similarities with a subset of human degenerative NP samples. Our findings underscore that maintenance of mitochondrial dynamics and multi-organelle cross-talk is critical in preserving metabolic homeostasis of disc and cartilage.