Mouse Models of Frailty: an Emerging Field.

Frailty is highly prevalent in the elderly, increasing the risk of poor outcomes that include falls, incident disability, hospitalization, and mortality. Thus, a great need exists to characterize the underlying mechanisms and ultimately identify strategies that prevent, delay, and even reverse frailty. Mouse models can provide insight into molecular mechanisms of frailty by reducing variability in lifestyle and genetic factors that can complicate interpretation of human clinical data. Frailty, generally recognized as a syndrome involving reduced homeostatic reserve in response to physiologic challenges and increasing susceptibility to poor health outcomes, is predominantly assessed using two independent strategies, integrated phenotype and deficit accumulation. The integrated phenotype defines frailty by the presentation of factors affecting functional capacity such as weight loss, exhaustion, low activity levels, slow gait, and grip strength. The deficit accumulation paradigm draws parameters from a greater range of physiological systems, such as the ability to perform daily activities, coordination and gait, mental components, physiological problems, and history and presence of medical morbidities. This strategic division also applies within the emerging field of mouse frailty models, with both methodologies showing usefulness in providing insight into physiologic mechanisms and testing interventions. Our review will explore the strategies used, caveats in methodology, and future directions in the application of animal models for the study of the frailty syndrome.