Catalysis of the reaction: a very-long-chain (3R)-3-hydroxyacyl-CoA + NADP+ = a very-long-chain 3-oxoacyl-CoA + H+ + NADPH. This reaction is the second (reduction) step of the four-step fatty acid elongation cycle in the endoplasmic reticulum that extends fatty acids of C-16 or longer with an additional 2-C unit.
Synonyms:
xref:
EC:1.1.1.330; MetaCyc:RXN-7698; RHEA:48680; Reactome:R-HSA-548818 "HSD17B3,12 hydrogenates 3OOD-CoA to 3HODC-CoA"