Brain alpha-amylase: a novel energy regulator important in Alzheimer disease?

Reduced glucose metabolism and formation of polyglucosan bodies (PGB) are, beside amyloid beta plaques and neurofibrillary tangles, well-known pathological findings associated with Alzheimer's disease (AD). Since both glucose availability and PGB are regulated by enzymatic degradation of glycogen, we hypothesize that dysfunctional glycogen degradation is a critical event in AD progression. We therefore investigated whether alpha (α)-amylase, an enzyme known to efficiently degrade polysaccharides in the gastrointestinal tract, is expressed in the hippocampal CA1/subiculum and if the expression is altered in AD patients. Using immunohistochemical staining techniques, we show the presence of the α-amylase isotypes AMY1A and AMY2A in neuronal dendritic spines, pericytes and astrocytes. Moreover, AD patients showed reduced gene expression of α-amylase, but conversely increased protein levels of α-amylase as well as increased activity of the enzyme compared with non-demented controls. Lastly, we observed increased, albeit not significant, load of periodic acid-Schiff positive PGB in the brain of AD patients, which correlated with increased α-amylase activity. These findings show that α-amylase is expressed and active in the human brain, and suggest the enzyme to be affected, alternatively play a role, in the neurodegenerative Alzheimer's disease pathology.

Molecular barcoding of viral vectors enables mapping and optimization of mRNA trans-splicing

Genome editing has proven to be highly potent in the generation of functional gene knockouts in dividing cells. In the CNS however, efficient technologies to repair sequences are yet to materialize. Reprogramming on the mRNA level is an attractive alternative as it provides means to perform in situ editing of coding sequences without nuclease dependency. Furthermore, de novo sequences can be inserted without the requirement of homologous recombination. Such reprogramming would enable efficient editing in quiescent cells (e.g., neurons) with an attractive safety profile for translational therapies. In this study, we applied a novel molecular-barcoded screening assay to investigate RNA trans-splicing in mammalian neurons. Through three alternative screening systems in cell culture and in vivo, we demonstrate that factors determining trans-splicing are reproducible regardless of the screening system. With this screening, we have located the most permissive trans-splicing sequences targeting an intron in the Synapsin I gene. Using viral vectors, we were able to splice full-length fluorophores into the mRNA while retaining very low off-target expression. Furthermore, this approach also showed evidence of functionality in the mouse striatum. However, in its current form, the trans-splicing events are stochastic and the overall activity lower than would be required for therapies targeting loss-of-function mutations. Nevertheless, the herein described barcode-based screening assay provides a unique possibility to screen and map large libraries in single animals or cell assays with very high precision.