Cell-Type Specific Regulation of Cholesterogenesis by CYP46A1 Re-Expression in zQ175 HD Mouse Striatum

Cholesterol metabolism dysregulation is associated with several neurological disorders. In Huntington's disease (HD), several enzymes involved in cholesterol metabolism are downregulated, among which the neuronal cholesterol 24-hydroxylase, CYP46A1, is of particular interest. The restoration of CYP46A1 expression in striatal neurons of HD mouse models is beneficial for motor behavior, cholesterol metabolism, transcriptomic activity, and alleviates neuropathological hallmarks induced by mHTT. Among the genes regulated after CYP46A1 restoration, those involved in cholesterol synthesis and efflux may explain the positive effect of CYP46A1 on cholesterol precursor metabolites. Since cholesterol homeostasis results from a fine-tuning between neurons and astrocytes, we quantified the distribution of key genes regulating cholesterol metabolism and efflux in astrocytes and neurons using in situ hybridization coupled with S100β and NeuN immunostaining, respectively. Neuronal expression of CYP46A1 in the striatum of HD zQ175 mice increased key cholesterol synthesis driver genes (Hmgcr, Dhcr24), specifically in neurons. This effect was associated with an increase of the srebp2 transcription factor gene that regulates most of the genes encoding for cholesterol enzymes. However, the cholesterol efflux gene, ApoE, was specifically upregulated in astrocytes by CYP46A1, probably though a paracrine effect. In summary, the neuronal expression of CYP46A1 has a dual and specific effect on neurons and astrocytes, regulating cholesterol metabolism. The neuronal restoration of CYP46A1 in HD paves the way for future strategies to compensate for mHTT toxicity.

Impact of Dietary Arachidonic Acid on Gut Microbiota Composition and Gut-Brain Axis in Male BALB/C Mice

Although arachidonic acid (ARA) is the precursor of the majority of eicosanoids, its influence as a food component on health is not well known. Therefore, we investigated its impact on the gut microbiota and gut-brain axis. Groups of male BALB/c mice were fed either a standard diet containing 5% lipids (Std-ARA) or 15%-lipid diets without ARA (HL-ARA) or with 1% ARA (HL + ARA) for 9 weeks. Fatty acid profiles of all three diets were the same. The HL-ARA diet favored the growth of Bifidobacterium pseudolongum contrary to the HL + ARA diet that favored the pro-inflammatory Escherichia-Shigella genus in fecal microbiota. Dietary ARA intake induced 4- and 15-fold colic overexpression of the pro-inflammatory markers IL-1β and CD40, respectively, without affecting those of TNFα and adiponectin. In the brain, dietary ARA intake led to moderate overexpression of GFAP in the hippocampus and cortex. Both the hyperlipidic diets reduced IL-6 and IL-12 in the brain. For the first time, it was shown that dietary ARA altered the gut microbiota, led to low-grade colic inflammation, and induced astrogliosis in the brain. Further work is necessary to determine the involved mechanisms.