Metabolic Engineering X

Bacterial Cell Factory for Production of Scyllo-Inositol, a Potential Therapeutic Agent for Alzheimer's Disease

Authors

Kosei Tanaka, Kobe University
Yoshihiro Toya, Osaka University
Hiroshi Shimizu, Osaka University

Inositol (1,2,3,4,5,6-cyclohexanehexol) has nine possible stereoisomers.  One of the stereoisomers, myo-inositol (MI), is most abundant in nature and supplied cheap from rice bran.  On the other hand, another stereoisomer, scyllo-inositol (SI), is rare in nature, and precious because of being expected as a disease-modifying therapeutic agent for Alzheimer’s disease, which is one of the most common and problematic forms of dementia.  It is known that aggregation of amyloid-beta in the brain is one of the key pathological features of Alzheimer's disease.  SI directly interacts with amyloid-beta and blocks the development of its fibrous aggregation.  In fact, oral administration of SI to a mouse model of Alzheimer's disease attenuated amyloid-beta-induced impairments of spatial memory, reduced cerebral amyloid-beta pathology, and decreased the rate of mortality.  And thus SI has received a fast-track designation from the US Food and Drug Administration for treatment of mild to moderate Alzheimer's disease. 

We demonstrated a cell factory, which enables bio-conversion from MI to SI, made of Bacillus subtilis with the modified inositol metabolic pathway.  In the B. subtilis cell factory, all “useless” genes involved in MI and SI metabolism were deleted, and in addition the two key enzymes responsible for the conversion, namely IolG and IolW, were overproduced under the control of one of the strongest promoters.  All of 1% (w/v) MI contained in the medium was converted into SI at the rate of 10 g/ L/ 48h at least.  The efficient conversion was achieved only in the presence of enriched nutrition in the form of 2% (w/v) Bacto soytone, which may be due to the increasing demand for regeneration of cofactors including NADPH.  The results from our transcriptomic and fluxomic analyses suggested that the regeneration of NADPH might be enabled by generic alternation in central carbon metabolism including enhancement in hexose monophosphate shunt and gluconeogenesis.