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Figure 2

Figure 2. From: Does Brown Fat Protect Against Diseases of Aging?.

Possible mechanisms by which BAT and mitochondrial uncoupling can protect against obesity and age-related diseases. See text for discussion.

Mark P. Mattson. Ageing Res Rev. ;9(1):69.

Figure 1. From: Does Brown Fat Protect Against Diseases of Aging?.

BAT: its location, cellular composition and thermogenic regulation. A. In humans brown adipose tissue (BAT) is located in interscapular and supraclavicular regions of the thorax, and is innervated by sympathetic nervous system (SNS) neurons that originate in the hypothalamus (HT) (Bamshad et al., 1999). Cold temperatures and excessive food intake activate the SNS resulting in increased BAT thermogenic activity. B. Cellular features of BAT. The principal cell of BAT is the brown adipose (BA) cell which contains large numbers of mitochondria that utilize energy substrates and O2 and generate heat which is transferred to circulating blood. BAT also contains brown adipose progenitors (BAP) which are capable of dividing and differentiation into BA cells. BAT is innervated by axons from sympathetic neurons that employ the neurotransmitter norepinephrine (NE). C. Thermogenic signal transduction in brown adipocytes. NE released from SNS presynaptic terminals activates adrenergic receptors (R) on the surface of BA cells, resulting in the activation of the GTP-binding protein gs which, in turn, activates adenylate cyclase (AC) to generate cyclic adenosine monophosphate (cAMP). Cyclic AMP then activates cAMP-dependent protein kinase (PKA) which then phosphorylates and thereby activates lipases that hydrolyze triacylglycerols to generate free fatty acids (FFA). The FFA are then transferred into mitochondria where they undergo β-oxidation to generate acetyl Co A (AcCoA) which enters the citric acid cycle (CAC). As a result of b-oxidation and the CAC the energy substrates FADH (flavanine adenine dinucleotide) and NADH (nicotinamide adenine dinucleotide) are generated. BA cells express high amounts of uncoupling protein 1 (UCP1) which, when activated by the pathway just described, mediates a proton leak that uncouples the electron transport chain resulting in heat production.

Mark P. Mattson. Ageing Res Rev. ;9(1):69.

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