Researchers here report that upregulation of α-Klotho and TGFβR2 together, via gene therapy, can modestly reverse osteoarthritis in a rat model in which untreated animals progress to a more severe stage of the condition. Inhibiting TGF-β receptors such as TGFβR2 is known to suppress chronic inflammation, and likely functions by interfering in the inflammatory TGF-β signaling produced by senescent cells. The evidence for cellular senescence to drive the progression of osteoarthritis is quite compelling at this point. Meanwhile, α-Klotho declines with age and upregulation of this protein is known to improve regenerative capacity in some tissues.
Osteoarthritis is caused by gradual changes to cartilage that cushions bones and joints. During aging and repetitive stress, molecules and genes in the cells of this articular cartilage change, eventually leading to the breakdown of the cartilage and the overgrowth of underlying bone, causing chronic pain and stiffness. Previous research had pinpointed two molecules, αKLOTHO and TGF beta receptor 2 (TGFβR2), as potential drugs to treat osteoarthritis. αKLOTHO acts on the mesh of molecules surrounding articular cartilage cells, keeping this extracellular matrix from degrading. TGFβR2 acts more directly on cartilage cells, stimulating their proliferation and preventing their breakdown.
Researchers treated young, otherwise healthy rats with osteoarthritis with viral particles containing the DNA instructions for making αKLOTHO and TGFβR2. Six weeks after the treatment, rats that had received control particles had more severe osteoarthritis in their knees, with the disease progressing from stage 2 to stage 4. However, rats that had received particles containing αKLOTHO and TGFβR2 DNA showed recovery of their cartilage: the cartilage was thicker, fewer cells were dying, and actively proliferating cells were present. These animals' disease improved from stage 2 to stage 1, a mild form of osteoarthritis, and no negative side effects were observed.
Further experiments revealed 136 genes that were more active and 18 genes that were less active in the cartilage cells of treated rats compared to control rats. Among those were genes involved in inflammation and immune responses, suggesting some pathways by which the combination treatment works. To test the applicability of the drug combination to humans, the team treated isolated human articular cartilage cells with αKLOTHO and TGFβR2. Levels of molecules involved in cell proliferation, extracellular matrix formation, and cartilage cell identity all increased.