Ectopic Gene Expression to Restore the Ascorbate Biosynthesis Pathway in Vertebrates Lacking Functional Gulo

Authors: Cao CR, Kelly R, Igdoura SA and Schellhorn HE*

Volume 2, Issue 1

Abstract

Background: Vitamin C (VC) deficiency is due to loss of the gene coding for ι-gulono-γ-lactone oxidase (Gulo). VC deficiency is an excellent candidate for therapeutic intervention by ectopic gene expression because a single gene mutation is responsible for the condition and, it is known, a priori, that supplementation effectively rescues the deficiency (at least with respect to the development of scurvy). There are several strategies to ectopically express exogenous genes or silence endogenous genes including viruses and nucleic acids, to ensure that the protein products encoded by exogenous genes are present in the cell, or those encoded by endogenous genes to be silenced are absent. Objective: We review strategies to restore ascorbate biosynthesis in vertebrates. We will discuss the physiology of vitamin C and evaluate the potential of the different methods for the restoration of Gulo expression, and subsequently the endogenous production of VC. Methods: Studies that have targeted manipulation of vitamin C synthesis in vertebrates, particularly the mouse model, over the last 20 years were examined. Results: Vectors of ectopic gene expression were identified as nucleic acids such as linear and plasmid DNA, mRNA, as well as viruses such as adenoviruses and lentiviruses. Direct enzyme replacement was identified as another method of Gulo expression. Conclusion: Ectopic gene expression can be used to rescue metabolic deficiency in VC synthesis using several different modes of delivery. New technologies that directly modify genomes (e.g. CRISPR) that have not yet been applied to this physiological deficiency may allow new investigations into VC physiology.

Keywords: Ascorbic acid; Vitamin C; Gulonolactone oxidase; Biosynthesis; Knockout; Gene expression; Vectors; Plasmids

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