Differential Efficiency and Pathway of Ribitol, Ribulose and Ribose for Enhancing Matriglycan Expression

Abstract

Glycosylation of alpha dystroglycan is critical for normal neural development and muscle function. Reduced or absence of glycosylation, specifically a terminal repeating biglycan units of 3GlcA-1-3Xyl-1 (matriglycan) on core M3, is the primary indication of numerous muscular dystrophies, and has a demonstrated effect in tumor development or metastasis. FKRP is a glycosyltransferase using CDP-ribitol as the substrate for addition of ribitol-5-phosphate to the core M3 and is essential for completing matriglycan synthesis. CDP-ribitol is synthesized with isoprenoid synthase domain containing (ISPD) using ribitol-5P and CTP as substrates. In this study, we examined a panel of pentoses and their phosphates for potential to enhance matriglycan synthesis in a cell culture system previously shown relevant to experimental therapy to dystroglycanopathy in vivo. Ribitol, ribulose, ribose and their phosphates all enhance matriglycan synthesis with highest efficiency by ribitol followed by ribulose and lowest by ribose. This is supported by metabolomics analysis showing that levels of ribitol-5P are significantly higher with ribitol and ribulose treatments than ribose. Enhanced matriglycan level by cytosine and its phosphates when combined with ribitol is demonstrated by immunocytochemistry. Ribose to ribulose to ribitol to ribitol-5P pathway is likely the predominant flow for synthesis of ribitol-5P when the pentoses are supplemented for enhancement of matriglycan expression as therapeutics. Ribitol is preferred for life-long treatment of FKRP-related dystroglycanopathy. Therapeutic potential of cytosine and its phosphates may be limited and remain to be explored in vivo.