Cerebral deposition of amyloid β peptide (Aβ) is an early and critical feature of Alzheimer's disease. Aβ generation depends on proteolytic cleavage of the amyloid precursor protein (APP) by two unknown proteases: β-secretase and γ-secretase. These proteases are prime therapeutic targets. A transmembrane aspartic protease with all the known characteristics of β-secretase was cloned and characterized. Overexpression of this protease, termed BACE (for beta-site APP-cleaving enzyme) increased the amount of β-secretase cleavage products, and these were cleaved exactly and only at known β-secretase positions. Antisense inhibition of endogenous BACE messenger RNA decreased the amount of β-secretase cleavage products, and purified BACE protein cleaved APP-derived substrates with the same sequence specificity as β-secretase. Finally, the expression pattern and subcellular localization of BACE were consistent with that expected for β-secretase. Future development of BACE inhibitors may prove beneficial for the treatment of Alzheimer's disease.

Five novel peptides were identified in the brains of mice lacking active carboxypeptidase E, a neuropeptide-processing enzyme. These peptides are produced from a single precursor, termed proSAAS, which is present in human, mouse, and rat. ProSAAS mRNA is expressed primarily in brain and other neuroendocrine tissues (pituitary, adrenal, pancreas); within brain, the mRNA is broadly distributed among neurons. When expressed in AtT-20 cells, proSAAS is secreted via the regulated pathway and is also processed at paired-basic cleavage sites into smaller peptides. Overexpression of proSAAS in the AtT-20 cells substantially reduces the rate of processing of the endogenous prohormone proopiomelanocortin. Purified proSAAS inhibits prohormone convertase 1 activity with an IC 50 of 590 nM but does not inhibit prohormone convertase 2. Taken together, proSAAS may represent an endogenous inhibitor of prohormone convertase 1.

We have analyzed the sequence and expression pattern of a BACE homolog termed BACE2. BACE and BACE2 are unique among aspartic proteases in that they possess a carboxyl-terminal extension with a predicted transmembrane region and together they define a new family. Northern analysis reveals that BACE2 mRNA is expressed at low levels in most human peripheral tissues and at higher levels in colon, kidney, pancreas, placenta, prostate, stomach, and trachea. Human adult and fetal whole brain and most adult brain subregions express very low or undetectable levels of BACE2 mRNA. In addition, in situ hybridization of adult rat brain shows that BACE2 mRNA is expressed at very low levels in most brain regions. The very low or undetectable levels of BACE2 mRNA in the brain are not consistent with the expression pattern predicted for ␤-secretase.

Delivery by CS is associated with a modest increased odds of ASD, and possibly ADHD, when compared to vaginal delivery. Although the effect may be due to residual confounding, the current and accelerating rate of CS implies that even a small increase in the odds of disorders, such as ASD or ADHD, may have a large impact on the society as a whole. This warrants further investigation.

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