Abundant type 10 17 beta-hydroxysteroid dehydrogenase in the hippocampus of mouse Alzheimer's disease model.

A full-length cDNA of mouse type 10 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD10) was cloned from brain, representing the accurate nucleotide sequence information that rendered possible an accurate deduction of the amino acid sequence of the wild-type enzyme. A comparison of sequences and three-dimensional models of this enzyme revealed that structures previously reported by other groups carry either a truncated or mutated amino-terminal sequence. Fusion of the first 11 residues of the wild-type enzyme to the green fluorescent protein directed the reporter protein into mitochondria. Thus, the N-terminus was identified as a mitochondrial targeting signal that accounts for the intracellular localization of the mouse enzyme. This enzyme is normally associated with mitochondria, not with the endoplasmic reticulum as suggested by its trivial name 'endoplasmic reticulum-associated amyloid-beta biding protein (ERAB)'. After its C-terminal region was used to raise rabbit anti-17 betaHSD10 antibodies, immunogold electron microscopy showed that an abundance of this enzyme could be found in hippocampal synaptic mitochondria of betaAPP transgenic mice, but not in normal controls. High levels of this enzyme may disrupt steroid hormone homeostasis in synapses and contribute to synapse loss in the hippocampus of the mouse Alzheimer's disease model.