CLUH is a cytosolic mRNA-binding protein that specifically binds a subset of mRNAs encoding mitochondrial proteins and may regulate their localized translation.

Epidemiological studies indicate that intake of statins decrease the risk of developing Alzheimer disease. Cellular and in vivo studies suggested that statins might decrease the generation of the amyloid ␤-peptide (A␤) from the ␤-amyloid precursor protein. Here, we show that statins potently stimulate the degradation of extracellular A␤ by microglia. The statin-dependent clearance of extracellular A␤ is mainly exerted by insulindegrading enzyme (IDE) that is secreted in a nonconventional pathway in association with exosomes. Stimulated IDE secretion and A␤ degradation were also observed in blood of mice upon peripheral treatment with lovastatin. Importantly, increased IDE secretion upon lovastatin treatment was dependent on protein isoprenylation and up-regulation of exosome secretion by fusion of multivesicular bodies with the plasma membrane. These data demonstrate a novel pathway for the nonconventional secretion of IDE via exosomes. The modulation of this pathway could provide a new strategy to enhance the extracellular clearance of A␤. Alzheimer disease (AD)3 is associated with extracellular deposits of the amyloid ␤-peptide (A␤) and intraneuronal aggregates of hyperphosphorylated Tau protein in the brain (1). Evidence suggests that the pathogenesis of AD involves deleterious neurotoxic effects of aggregated A␤ peptides (2), which are derived by sequential proteolytic processing of the ␤-amyloid precursor protein (APP) by ␤-and ␥-secretases (3). APP can also be cleaved in a nonamyloidogenic pathway that involves initial cleavage by ␣-secretase within the A␤ domain that precludes the later generation of A␤ peptides (4). Brain A␤ levels are not only determined by the rate of production but also by different clearance mechanisms, including receptor-mediated endocytosis/phagocytosis and subsequent degradation in the endosomal/lysosomal compartment, transcytosis via the blood-brain barrier, as well as proteolytic degradation of extracellular A␤ by cell surface-localized and secreted proteases (5-10).Several studies indicated a dysregulation of lipid metabolism as an important aspect of AD-associated neurodegeneration. In particular, increased cholesterol levels seem to correlate with increased AD risk. Retrospective studies revealed the beneficial effects of statins (11). However, molecular mechanisms by which statins could offer protection against AD remain to be characterized in detail (12, 13). Most studies with cultured cells and animal models indicate that statin-mediated inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) could decrease the generation of A␤ by promoting nonamyloidogenic processing of APP. Other studies also showed that extraction of cholesterol from cellular membranes by cyclodextrins differentially affects A␤ generation. Although strong reduction of cholesterol decreased A␤ generation, a moderate extraction rather promoted the secretion of A␤. These effects were attributed to alterations in the distribution of APP and secretases within membrane microdomains (14 -18). In ...

CLUH binds mRNAs implicated in intermediate metabolism and oxidative phosphorylation, but the physiological and molecular significance of these interactions is unclear. Schatton et al. use new constitutive and liver-specific Cluh knockouts to define the function of CLUH in catabolic and energy-converting pathways as a regulator of the translation and stability of target mRNAs.