How Aging Causes Osteoarthritis: An Evolutionary Physiology Perspective

Late-life diseases result from the poorly understood process of senescence (aging), that is largely genetically determined. According to a recently proposed evolutionary physiology-based account, the multifactorial model, senescence is largely caused by evolved but non-adaptive programmatic mechanisms specified by the wild-type (i.e. normal) genome. These act together with disruptions to wild-type function (due e.g. to infectious pathogens, mechanical injury and malnutrition) in a variety of combinations to generate diverse late-life diseases. Here the utility of this model is explored by testing its capacity to provide an account of one complex, late-life disease, osteoarthritis (OA), and a framework for understanding OA etiology suggested. In this framework, the core OA disease mechanism is a futile endochondral ossification quasi-program (non-adaptive developmental program), in which hypertrophic articular chondrocytes alter joint architecture. Programmatic changes prime chondrocytes for quasi-program activation, which can be triggered by secondary causes of OA (e.g. joint mechanical injury). A suggested evolutionary cause of this priming, involving antagonistic pleiotropy, is selection to maximize early life tissue repair benefits at the expense of late-life programmatic costs.