. 2021 Oct 30;10(11):1746. doi: 10.3390/antiox10111746

Table 1.

Expression and hypothesized functions of all mitochondrial uncoupling proteins (UCPs) homologs.

Isoform	Localization	Putative Function	References
UCP1	Human brown adipose tissue, white adipose tissue, keratinocytes, sweat glands, sebum glands, hair follicles, and granular layer of the epidermis	Non-shivering thermogenesis, metabolic and bioenergetic regulation, modulation of ROS production	[21,22,23]
	Mouse brown adipose tissue, white adipose tissue, and adrenal gland		[24,25,26]
	Rat brown adipose tissue and white adipose tissue		[27,28]
UCP2	Human proximal tubular cells, cytotrophoblasts, syncytiotrophoblast, lungs , keratinocytes , skin fibroblasts , spermatozoa, white adipose tissue , skeletal muscle , brown adipose tissue , and pancreatic β-cells *, brain	Modulation of ROS production, insulin sensitivity and secretion, lipid and glucose metabolism, control of mitochondrial Ca²⁺-uptake, inflammation, immunomodulation	[23,29,30,31,32,33,34,35]
	Mouse thymocytes, tubular epithelial cells, granulosa cells , theca cells , endometrium glandular epithelium cells , uterine glands , oviduct mucosa epithelial cells , mammary gland, stomach, macrophages, splenocytes, B lymphocytes, T lymphocytes, dendritic cells, neutrophils, microglial cells , neurons , cardiomyocytes, lungs, testicular germ cells, testicular interstitial cells, white adipose tissue , skeletal muscle , brown adipose tissue , pancreatic β-cells , pancreatic α-cells, and hepatocytes		[13,34,35,36,37,38,39,40,41,42,43,44,45,46]
	Rat proximal tubular cells, Kupffer cells , microglial cells, neurons, cardiomyocytes, skeletal muscle , testis, brown adipose tissue , white adipose tissue , pancreatic β-cells, lungs , spleen , and thymus *		[33,47,48,49,50,51,52,53,54,55,56]
UCP3	Human skeletal muscle, heart , spleen , thymus , keratinocytes , skin fibroblasts, sweat glands, hair follicles, stratum basale of the epidermis, pancreatic β-cells, thyroid , and bone marrow	Modulation of ROS production, insulin secretion, lipid metabolism, protection against lipotoxicity, control of mitochondrial Ca²⁺-uptake, immunomodulation	[23,33,57,58,59,60]
	Mouse skeletal muscle, brown adipose tissue, brain , kidney , colon , liver , heart, white adipose tissue, thymocytes, splenic lymphocytes, and peripheral naive CD4+ T cells *		[60,61,62,63]
	Rat skeletal muscle, brown adipose tissue , white adipose tissue , kidney *, spleen reticulocytes, spleen monocytes, spleen lymphocytes, thymocytes, and heart		[33,52,57,64]
UCP4	Human Purkinje cells, most of the brain tissues , and cartilage	Regulation of oxidative stress, thermoregulation, protection against mitochondrial Ca²⁺ overload	[7,9,15,65]
	Rat Merkel cells, modiolus ear (fibrocyte, satellite cells), organ of Corti (spiral ganglion neurons, supporting cells, hair cells), brain (pyramidal cells of hippocampus and cortex, Purkinje cells of cerebellum, neurons of hippocampus, substantia nigra, striatum, neocortex ), chondrocytes, vestibular ganglion , heart , lungs , skeletal muscle , kidney , and liver *		[7,55,65,66,67,68,69]
	Mouse brain (neurons, astrocytes, cortex, brainstem, cerebellum), spinal cord, mast cells, spiral ganglion , vestibular ganglion , kidney , heart , white adipose tissue , brown adipose tissue , skeletal muscle , and liver		[55,66,70,71,72]
UCP5	Human kidney , heart , lungs , stomach , liver , spleen , skeletal muscle , brain (cerebellum, cortex, medulla, occipital pole, frontal lobe, putamen, amygdala, caudate nucleus, hippocampus, substantia nigra, thalamus, corpus callosum) , spinal cord , pituitary , uterus , and testis	Regulation of oxidative stress, thermoregulation, transport of metabolites, regulation of mitochondrial metabolism	[14,73,74]
	Rat heart , lungs , adrenals , kidney , gonadal fat , ovary , brain (striatum, cortex, hippocampus, cerebellum) , skeletal muscle , and liver *		[14,55,75]
	Mouse heart, kidney, skeletal muscle, white adipose tissue, spinal cord, brain (neurons, astrocytes, cortex, thalamus, hippocampus, substantia nigra, cerebellum, basal ganglia, hypothalamus , amygdala , neocortex , caudate putamen ), spiral ganglion , vestibular ganglion , hepatocytes, brown adipose tissue , spleen , intestine , lungs , testis , uterus , and periovarian fat		[14,30,44,71,72,74,76,77,78]
UCP6	Mouse kidney (proximal tubules, distal tubules, surrounding nephron segments, glomeruli, medullary part of the loop of Henle, collecting duct) , white adipose tissue , brown adipose tissue , brain , heart , muscle , liver , lungs , spleen , and testis	Regulation of oxidative stress, transport of metabolites, regulation of mitochondrial metabolism	[30,74]

* Only mRNA has been reported or predicted based on mRNA microarrays.