Adipose and skeletal muscle thermogenesis: studies from large animals

Abstract

The balance between energy intake and energy expenditure establishes and preserves a 'set-point' body weight. The latter is comprised of three major components including metabolic rate, physical activity and thermogenesis. Thermogenesis is defined as the cellular dissipation of energy via heat production. This process has been extensively characterised in brown adipose tissue (BAT), wherein uncoupling protein 1 (UCP1) creates a proton leak across the inner mitochondrial membrane, diverting protons away from ATP synthesis and resulting in heat dissipation. In beige adipocytes and skeletal muscle, thermogenesis can occur independent of UCP1. Beige adipocytes have been shown to produce heat via UCP1 as well as via both futile creatine and calcium cycling pathways. On the other hand, the UCP1 homologue UCP3 is abundant in skeletal muscle and post-prandial thermogenesis has been associated with UCP3 and the futile calcium cycling. This review will focus on the differential contributions of adipose tissue and skeletal muscle in determining total thermogenic output and energy expenditure in large mammals. Sheep and pigs do not have a circumscribed brown fat depot but rather possess white fat depots that contain brown and beige adipocytes interspersed amongst white adipose tissue. This is representative of humans, where brown, beige and white adipocytes have been identified in the neck and supraclavicular regions. This review will describe the mechanisms of thermogenesis in pigs and sheep and the relative roles of skeletal muscle and adipose tissue thermogenesis in controlling body weight in larger mammals.

Adaptive thermogenesis enhances the life-threatening response to heat in mice with an Ryr1 mutation

“…Consistent with the potentially lethal heat response in children with MHS, we found that the YS mice display a life-threatening response to heat that is also more severe in young mice and displays male predominance. Since adaptive thermogenesis, the finely regulated bioenergetic process that produces heat in response to changes in environmental temperature or diet [90][91][92] , plays a crucial role in the regulation of body temperature, we assessed the contribution of adaptive thermogenesis to the heat sensitivity of the YS mice. BAT and skeletal muscle are the principal sites for adaptive thermogenesis.…”

Neuronatin regulates whole‐body metabolism: is thermogenesis involved?

“…37 Skeletal muscle comprises 40%-50% of the mammalian body. 38 Due to its highly energetically active nature and abundance in the body, skeletal muscle accounts for 20%-25% of total BMR. 39 The main contributor to energy expenditure in skeletal muscle are the SERCA pumps, which account for nearly 50% of resting metabolic rate in skeletal muscle.…”

Transcriptional Changes Involved in Atrophying Muscles during Prolonged Fasting in Rats

“…Skeletal muscles can also be seen as a reservoir of amino acids, whose mobilization can serve for protein synthesis in various organs [1], and for liver glucose neosynthesis to ensure maintenance of glycemia during food deprivation [7]. In addition, a significant thermogenic role for skeletal muscle has been strongly suggested [8]. Finally, skeletal muscle exerts a number of endocrine or paracrine effects on various physiological processes through the production of the so-called myokines [9].…”