Messenger RNA as novel treatment strategy for Hereditary Spastic Paraplegia Type 5 (SPG5): Developing a Messenger RNA Therapy for SPG5

Hereditary spastic paraplegia type 5 is a neurodegenerative disease caused by loss-of-function mutations in the CYP7B1 gene encoding the oxysterol 7-α-hydroxylase involved in bile acid synthesis in the liver. Lack of CYP7B1 leads to an accumulation of its oxysterol substrates, in particular 25-hydroxycholesterol and 27-hydroxycholesterol that are able to cross the blood-brain barrier and have neurotoxic properties. A potential therapeutic strategy for SPG5 is the replacement of CYP7B1 by administration of mRNA. Here, we studied the intravenous application of formulated mouse and human CYP7B1 mRNA in mice lacking the endogenous Cyp7b1 gene. A single-dose injection of either mouse or human CYP7B1 mRNA led to a pronounced degradation of oxysterols in liver and serum within 2 days of treatment. Pharmacokinetics indicate a single injection of human CYP7B1 mRNA to be effective in reducing oxysterols for at least 5 days. Repetitive applications of mRNA were safe for at least 17 days and resulted in a significant reduction of neurotoxic oxysterols not only in liver and serum but also to some extent in the brain. Our study highlights the potential to use mRNA as a novel therapy to treat patients with SPG5 disease.