Early whole-body mutant huntingtin lowering preserves proteins and lipids important for synapse function and white matter maintenance in the LacQ140 mouse model

Lowering mutant huntingtin (mHTT) transcription is a promising approach to treat Huntington's disease (HD). Using a mHtt-inducible mouse model we analyzed mHtt lowering initiated at different ages and sustained for different time-periods. mHTT protein in cytoplasmic and synaptic compartments of the caudate putamen, which is most affected in HD, was reduced 38-52%. Little or no lowering of mHTT occurred in nuclear and perinuclear regions where aggregates formed at 12 months of age. mHtt transcript repression partially or fully preserved select striatal proteins (SCN4B, PDE10A). Total lipids in striatum were reduced in LacQ140 mice at 9 months and preserved by early partial mHtt lowering. The reduction in total lipids was due in part to reductions in subclasses of ceramide (Cer), sphingomyelin (SM), and monogalactosyl diglyceride (MGDG), which are known to be important for white matter structure and function. Lipid subclasses- phosphatidylinositol (PI), phosphatidylserine (PS), and bismethyl phosphatidic acid (BisMePA)- were also changed in LacQ140 mice. Levels of all subclasses other than ceramide were preserved by early mHtt lowering. Our findings suggest that early and sustained reduction in mHtt can prevent changes in levels of select striatal proteins and most lipids but a misfolded, degradation-resistant form of mHTT hampers some benefits in the long term. ### Competing Interest Statement KBK-G spouse owns less than 0.1% stock in the following companies: Advanced Microdevices, Aveo Pharmaceuticals, Inc, Boston Scientific Corporation, Bristol-Myers Squibb Company, Cisco Systems, Inc., Fate Therapeutics, GE Healthcare Life Sciences, Generex Biotechnology Corporation, Idera Pharmaceuticals, Inc., Nante Health, Neurometrics, Inc., NuGenerex, Repligen Corporation, Sesen Bio, Inc., T2 Biosystems, and Vericel Corporation. Other authors have no declarations of interest.