Infusion of Lanosterol to Restore Cholesterol Metabolism in R6/2 Mice: A Research Protocol

Abstract

Huntington’s disease (HD) is an autosomal-dominant, neurodegenerative disease characterized by motor dysfunction, cognitive decline, and drastic behavioural changes. The mutant huntingtin gene contains a CAG trinucleotide repeat resulting in a polyglutamine expansion in the mutant huntingtin protein (muHTT). While the mechanisms are not yet fully understood, muHTT is linked to the disruption of nerve and glial cells, particularly in their role in synthesizing cholesterol. Abnormal interactions between muHTT and sterol regulatory element-binding proteins (SREBP), which are transcription factors that control the cholesterol biosynthesis pathway, are implicated in HD. About 25% of the human body’s total cholesterol is found in the brain and is involved in many vital roles, such as synaptogenesis, axonal growth, and creating efficient synaptic transmissions. Cholesterol biosynthesis is shown to be diminished in HD models, along with decreased levels of cholesterol precursor molecules, thus lowered cholesterol levels may be linked to the symptoms and progression of HD. This protocol aims to increase cholesterol biosynthesis by infusion of lanosterol, a cholesterol precursor, in R6/2 mice via osmotic mini-pumps. Three increasing doses of lanosterol will be administered to three groups of R6/2 mice, while one R6/2 and one wild type group will receive saline. These doses will be administered continuously over 7 weeks, starting from age 6-weeks when mice begin displaying progressive R6/2 symptoms until age 12-weeks when they show end-stage disease. Seven weekly rounds of tests will be conducted to assess motor and cognitive functioning, consisting of a rotarod performance test, Morris Water Maze test, and Novel Object Recognition test. At age 12-weeks, the mice will be sacrificed for immunohistochemistry analysis, gas chromatography-mass spectrometry, and flow cytometry to compare muHTT aggregate numbers, cholesterol levels, and striatal neuron count between the treatment and control mice. As a result of restored cholesterol homeostasis, amelioration in motor defects, cognitive performance, and striatal neuron survival rate in lanosterol-receiving mice compared to controls are expected. These anticipated results would suggest that lanosterol infusion via osmotic mini-pumps holds therapeutic potential and could be used to improve the prognosis of HD patients.