Divergent amino acid and sphingolipid metabolism in patients with inherited neuro-retinal disease

Abstract

The non-essential amino acids serine, glycine, and alanine, as well as diverse sphingolipid species, are implicated in inherited neuro-retinal disorders and are metabolically linked by serine palmitoyltransferase (SPT), a key enzyme in membrane lipid biogenesis. To gain insights into the pathophysiological mechanisms linking these pathways to neuro-retinal diseases we performed a targeted metabolomic analysis of these pathways in sera from patients diagnosed with two metabolically intertwined diseases: macular telangiectasia type II (MacTel), hereditary sensory autonomic neuropathy type 1 (HSAN1), or both. In a cohort of >350 participants, MacTel patients exhibited broad alterations of amino acids, including changes in serine, glycine, alanine, glutamate, and branched-chain amino acids reminiscent of diabetes. MacTel patients had elevated 1-deoxysphingolipids but reduced levels of complex sphingolipids in circulation. A mouse model indicates this depletion in complex sphingolipids can be driven by low dietary serine and glycine. HSAN1 patients exhibited elevated serine, lower alanine, and a reduction in canonical ceramides and sphingomyelins compared to controls. Those patients diagnosed with both HSAN1 and MacTel showed the most significant decrease in circulating sphingomyelins. These results highlight metabolic distinctions between these two diseases, emphasize the importance of membrane lipids in the progression of MacTel, and suggest distinct therapeutic approaches.