Year: 2015
Type: article
Abstract: We are using AAV-based gene therapy to restore cholesterol biosynthesis in a mouse model for Smith Lemli Opitz syndrome (SLOS). Mutations in the 7-dehydrocholesterol reductase gene (DHCR7) are responsible for this inborn error resulting in cholesterol deficiency and accumulation of potentially toxic 7-and 8-dehydrocholesterol (DHC) precursors. The central nervous system (CNS) is significantly impacted in affected individuals; present forms of therapy by dietary cholesterol supplementation fail to restore cholesterol homeostasis in these tissues due to the blood brain barrier (BBB). Previously, we showed that intravenous gene therapy using AAV vectors had a positive effect on systemic cholesterol homeostasis, but that cholesterol metabolism in the CNS was unaffected. To target the CNS and bypass the restrictive BBB, an AAV2/8 vector carrying a normal copy of the human DHCR7 gene was introduced into the cerebrospinal fluid via intrathecal injection. Three-day-old SLOS mice (compound heterozygotes containing a null allele and a hypomorphic allele of Dhcr7) were treated and 8 weeks later various nervous and non-nervous tissues were analyzed for sterols by gas chromatography and mass spectrometry. Resulting data were expressed as the DHC/cholesterol ratio, an index of SLOS biochemical severity. In addition the presence of the rescue gene and expression of its mRNA in the CNS were evaluated by real-time quantitative PCR. We observed partial normalization of the DHC/cholesterol ratio in the brain and spinal cord of treated mice. A similar effect was also noted in the sciatic nerves, which form part of the peripheral nervous system. In contrast, sterol levels in the liver, which received little or no vector, were not significantly affected. In brain the extent of improvement in the DHC/cholesterol ratio correlated with the level of vector DNA and the level of human DHCR7 mRNA expression indicating a dose/response relationship. The effect of neonatal vector administration was sustained into adulthood, to at least 8 weeks of age. Thus, vector and its expression persisted through the postnatal period of dramatic growth and tissue expansion. These results demonstrate the first potential means of treating the nervous system in SLOS patients. We suggest that providing treatment early in nervous system development could minimize and possibly to some extent even reverse the effects of inherited cholesterol deficiency. Used in combination with systemic gene delivery, this means of treatment may result in providing (the most) effective overall treatment for this debilitating disorder.
Source: Molecular Therapy
Language: English
Subfield: Genetics
Domain: Life Sciences
Open Access status: hybrid
Estimated APC paid: $4,500
OpenAlex ID: W2561060218