Links between thermoregulation and aging in endotherms and ectotherms

Abstract

While the link between thermoregulation and aging is generally accepted, much further research, reflection, and debate is required to elucidate the physiological and molecular pathways that generate the observed thermal-induced changes in lifespan. Our aim in this review is to present, discuss, and scrutinize the thermoregulatory mechanisms that are implicated in the aging process in endotherms and ectotherms. Our analysis demonstrates that low body temperature benefits lifespan in both endothermic and ectothermic organisms. Research in endotherms has delved deeper into the physiological and molecular mechanisms linking body temperature and longevity. While research in ectotherms has been steadily increasing during the past decades, further mechanistic work is required in order to fully elucidate the underlying phenomena. What is abundantly clear is that both endotherms and ectotherms have a specific temperature zone at which they function optimally. This zone is defended through both physiological and behavioral means and plays a major role on organismal senescence. That low body temperature may be beneficial for lifespan is contrary to conventional medical theory where reduced body temperature is usually considered as a sign of underlying pathology. Regardless, this phenomenon has been targeted by scientists with the expectation that advancements may compress morbidity, as well as lower disease and mortality risk. The available evidence suggests that lowered body temperature may prolong life span, yet finding the key to temperature regulation remains the problem. While we are still far from a complete understanding of the mechanisms linking body temperature and longevity, we are getting closer.

Keywords: ambient temperature; body temperature; brown adipose tissue; cold exposure; lifespan; longevity.

Figure 1.

The age-associated increase in pathophysiology/disease susceptibility leading to tissue damage and physical decline, as well as the impact of genetic and environmental factors.

Figure 2.

The key avenues of heat exchange between the body and the environment that, ultimately, determine body temperature in endotherms and ectotherms.

Figure 3.

A conceptual model illustrating the mechanisms linking caloric restriction and reduced body temperature (Tb) and their influence on longevity. Adapted from: Carrillo AE, Flouris AD. Caloric restriction and longevity: effects of reduced body temperature. Aging Res Rev 2011; 10:153–62. Note: BAT = brown adipose tissue; UCP1 = uncoupling protein one; ROS = reactive oxygen species.

Figure 4.

The mechanisms of heat exchange in aquatic, diurnal, and nocturnal amphibians.

Figure 5.

The mechanisms through which thermoregulation may be implicated in the aging process in endotherms (A) and ectotherms (B).