Table 1.

Summary of CTRPs and their potential metabolic functions.

CTRP	Tissue distribution	Regulation	Signaling specificity	Sites of action	Physiological function	Reference
CTRP1	Primarily adipose tissue and placenta	Decreased expression and circulating levels in DIO mice; increased expression in adiponectin KO mice	AMPK 44/42-MAPK	Skeletal muscle	Promotes glucose uptake and skeletal muscle fat oxidation; decrease fat mass and enhances insulin sensitivity in transgenicmice fed a high-fat diet	29, 36, 48
CTRP2	Primarily adipose tissue; lower levels in lung, liver, testis, uterus	Increased expression in the adipose tissue of ob/ob mice	AMPK	Skeletal muscle ?	Promotes fatty acid oxidation in cultured C2C12 myotubes	36
CTRP3	Adipose tissue, kidney, testis, uterus, bone	Decreased expression and circulating levels in DIO mice; increased expression in overnight fasted mice	AKT	Liver	Suppresses hepatic gluconeogenic gene expression and glucose output; ameliorates diet-induced hepatic steatosis by inhibiting liver triglyceride synthesis	36, 49 99, 109, 112–116
			p44/42-MAPK p38-MAPK	Endothelial cells	Inceases migration and proliferation of endothelial cells in vitro
			AKT	Heart	Increases survival and decreases infarct size following myocardial infarction
			?	Monocytes, adipocytes and colonic fibroblasts	Decreases LPS-induced inflammatory response
CTRP5	Adipose tissue, eye, testis skeletal muscle, brain spleen, uterus	Circulating levels of CTRP5 are increased in db/db and ob/ob mice, and OLETF rats	AMPK	Skeletal muscle ?	Inreases glucose uptake and fatty acid oxidation in mitochondriadepleted myotubes in vitro	29, 36, 84, 117–123
				Eye	S163R mutation results in late-onset retinal maculardegeneration in humans
CTRP6	Primarily placenta; much lower levels in spleen, lung, testis, prostate, uterus, adipose tissue	Increased expression in the adipose tissue of ob/ob mice; rosiglitazone treament decrease expression in the adipose tissue	?	?	?	29, 36
CTRP7	Primarily adipose tissue and lung	?	?	?	?	29, 36
CTRP9	Primarily adipose tissue	Decreased circulating levels in DIO mice; Increased expression and circulating levels in fasted/re-fed mice	AMPK	Skeletal muscle	Promotes fat oxidation	47, 124, 130–133,
			AMPK/eNOS	Endothelial cells	Vasorelaxation
			AMPK	Heart	Improved cardiac function following ischemia/reperfusion injury
			p44/42-MAPK PKA	Vascular smooth muscle cells	Increased migration and cell proliferation; reduces neointima formation
CTRP11	Primarily adipose tissue and testis; lower levels in brain and kidney	Increased expression in the adipose tissue of fasted/re-fed mice	p44/42-MAPK	Pre-adipocytes	Inhibit adipogenesis	52
CTRP12	Primarily adipose tissue in humans; primarily testis, adipose, kidney, spleen, uterus in mice	Decreased expression and circulating levels in ob/ob and DIO mice	AKT	Adipose tissue	Promotes glucose uptake in adipocytes	50, 54,75, 141
			AKT	Liver	Suppresses hepatic gluconeogenic gene expression and glucose output
			?	Pancreatic β-cells ?	Enhances insulin secretion inlean but not DIO mice; increases glucose-induced insulin secretion in INS-1 cells
			?	Adipose tissue	Suppresses adipose tissue inflammation
CTRP13	Primarily adipose, brain, and kidney	Increased expression in the adipose tissue of ob/ob ice and in adipocytes treated with rosiglitazone	AMPK	Adipocytes, myotubes, and hepatocytes	Promotes glucose uptake in cultured adipocytes, myotubes, and hepatocytes	51, 142
			AMPK	Liver ?	Suppressed gluconeogenic gene expression and glucose production in cultured H4IIEhepatocytes
			?	Liver ?	Decreased palmitate-induced insulin resistance in cultured hepatocytes by suppressing JNK signaling
			?	Hypothalamus	Suppressed food intake in mice by inhibiting orexigenic neuropeptide (NPY) expression
Myonectin (CTRP15)	Primarily skeletal muscle	Decreased expression and circulating levels in fasted mice and strikingly induced in fasted/re-fed mice	?	Adipose tissue and liver	Promotes lipid uptake by increasing the expression of molecules (FATP, FABP) involved in fatty acid uptake	53