Non‐specific accumulation of glycosphingolipids in GNE myopathy

Abstract

Background UDP-GlcNAc 2-epimerase/ManNAc 6-kinase (GNE) is a bifunctional enzyme responsible for the first committed steps in the synthesis of sialic acid, a common terminal monosaccharide in both protein and lipid glycosylation. GNE mutations are responsible for a rare autosomal recessive neuromuscular disorder, GNE myopathy (also called hereditary inclusion body myopathy). The connection between the impairment of sialic acid synthesis and muscle pathology in GNE myopathy remains poorly understood. Methods Glycosphingolipid (GSL) analysis was performed by HPLC in multiple models of GNE myopathy, including patients’ fibroblasts and plasma, control fibroblasts with inhibited GNE epimerase activity through a novel imino sugar, and tissues of GneM712T/M712T knock-in mice. Results Not only neutral GSLs, but also sialylated GSLs, were significantly increased compared to controls in all tested models of GNE myopathy. Treatment of GNE myopathy fibroblasts with N-acetylmannosamine (ManNAc), a sialic acid precursor downstream of GNE epimerase activity, ameliorated the increased total GSL concentrations. Conclusion GNE myopathy models have increased total GSL concentrations. ManNAc supplementation results in decrease of GSL levels, linking abnormal increase of total GSLs in GNE myopathy to defects in the sialic acid biosynthetic pathway. These data advocate for further exploring GSL concentrations as an informative biomarker, not only for GNE myopathy, but also for other disorders of sialic acid metabolism.

GNE myopathy: from clinics and genetics to pathology and research strategies

“…These data may lead to further studies of glycosphingolipids concentrations as a potential biomarker, not only for GNE myopathy, but also for other disorders of sialic acid metabolism. Indeed, when studying the tissue of Gne (p.M712 T/p.M712 T; according to the new nomenclature p.M743 T/p.M743 T) knock-in mice (described below in more detail) elevated glycosphingolipids concentrations could also be observed supporting the concept of glycosphingolipids concentrations as a biomarker [ 52 ]. By focusing on the same mutation in primary patient –derived myoblasts cultures, Amsili and colleagues [ 53 ] identified that although p.M712 T-mutant GNE and control myoblasts showed similar patterns of proliferation and differentiation, upon apoptosis induction, active forms of caspase-3 and -9 were strongly increased in p.M712 T-GNE cultures compared to controls, while pAKT, downregulated in controls, remained high in patient-derived cells.…”

“…Patzel and co-workers [ 52 ] investigated the accumulation of glycosphingolipids by HPLC in patients’ and control fibroblasts and plasma. The mutant cells exhibited impaired GNE epimerase activity through a novel imino sugar resulting in an increase of both, neutral and sialylated glycosphingolipids.…”

Mutation Update forGNEGene Variants Associated with GNE Myopathy

“…Therefore, impaired sialylation appears to be a main contributor to the still elusive disease pathology [Noguchi et al., ; Sparks et al., ; Malicdan et al., ; Malicdan et al., ]. Although overall sialylation of tissues appears to be normal in GNE myopathy, specific circulating proteins and/or specific muscle glycoproteins or glycolipids appear hyposialylated [Huizing et al., ; Tajima et al., ; Ricci et al., ; Broccolini et al., ; Patzel et al., ].…”

CDG Therapies: From Bench to Bedside

“…Other important in vitro models are patient-derived cells, such as fibroblasts, leukocytes or muscle cells which have been used to test biochemical and cellular features as well as responses to potential treatments. [ 23 , 27 , 36 , 40 , 43 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 ]…”

“…Evidence that supplementation of SA precursors, such as the aminosugars ManNAc or d -mannosamine (ManN), can bypass GNE defects has been obtained in a set of different disease models ( Figure 2 ) [ 19 , 74 , 78 , 81 , 109 , 110 , 206 , 207 ]. ManNAc treatment restored glycosphingolipid (GSL) levels in patient cells [ 66 ] and up-regulated Gne and protein expression, therefore suggesting that this aminosugar may act as a protein stabilizer [ 80 , 81 ]. As many GNE-CDG patients are likely to be diagnosed only in adulthood, the effects of oral ManNAc, SA or ManN therapy in adult mutant mice were tested, demonstrating that all of these compounds rescued kidney and muscle hyposialylation [ 78 ].…”