Glycoprotein Hyposialylation Gives Rise to a Nephrotic-Like Syndrome That Is Prevented by Sialic Acid Administration in GNE V572L Point-Mutant Mice

Abstract

Mutations in the key enzyme of sialic acid biosynthesis, UDP-N-acetylglucosamine 2-epimerase/N-acetyl-mannosamine kinase, result in distal myopathy with rimmed vacuoles (DMRV)/hereditary inclusion body myopathy (HIBM) in humans. Sialic acid is an acidic monosaccharide that modifies non-reducing terminal carbohydrate chains on glycoproteins and glycolipids, and it plays an important role in cellular adhesions and interactions. In this study, we generated mice with a V572L point mutation in the GNE kinase domain. Unexpectedly, these mutant mice had no apparent myopathies or motor dysfunctions. However, they had a short lifespan and exhibited renal impairment with massive albuminuria. Histological analysis showed enlarged glomeruli with mesangial matrix deposition, leading to glomerulosclerosis and abnormal podocyte foot process morphologies in the kidneys. Glycan analysis using several lectins revealed glomerular epithelial cell hyposialylation, particularly the hyposialylation of podocalyxin, which is one of important molecules for the glomerular filtration barrier. Administering Neu5Ac to the mutant mice from embryonic stages significantly suppressed the albuminuria and renal pathology, and partially recovered the glomerular glycoprotein sialylation. These findings suggest that the nephrotic-like syndrome observed in these mutant mice resulted from impaired glomerular filtration due to the hyposialylation of podocyte glycoproteins, including podocalyxin. Furthermore, it was possible to prevent the nephrotic-like disease in these mice by beginning Neu5Ac treatment during gestation.

Systemic Blockade of Sialylation in Mice with a Global Inhibitor of Sialyltransferases

“…These changes are likely a reflection of the loss of sialic acid on podocalyxin, a highly sialylated glycoprotein on glomerular podocytes that forms an electrostatic barrier integral to the filtering capacity of glomeruli (42). Indeed, loss of sialylation on podocalyxin is known to cause kidney dysfunction in patients as well as mice with mutations in glucosamine [UDP-N-acetyl]-2-epimerase/N-acetylmannosamine kinase and cytidine monophosphate N-acetylneuraminic acid synthetase (32)(33)(34). The resialylation of podocalyxin by day 54 as seen by Western blot but continued loss of kidney function may reflect the desialylation on other highly sialylated proteins, such as nephrin, which also serves a critical filtration role in podocytes (34).…”

“…It is noteworthy that although blockade of sialylation with 3F-NeuAc did not alter the viability of cultured cells (29), genetic disruption of sialic acid biosynthesis is embryonically lethal in mice (10). In contrast, transgenic mice with partial disruption of sialic acid biosynthesis (32)(33)(34) or deficiencies in expression of individual sialyltransferases are viable and have very selective and often subtle phenotypes (16 -28), making it difficult to predict the effect of a sialyltransferase inhibitor post-development.…”

Sialyllactose ameliorates myopathic phenotypes in symptomatic GNE myopathy model mice

“…Given that large amounts of sialic acid may be needed to rescue muscle atrophy, in addition to contractile property, there are several points that we must consider to achieve an efficient increase in sialic acid level in peripheral tissues, including the pharmacological advantages of the less metabolized compounds such as 6'-sialyllactose; high cellular uptake of compounds such as peracetylated ManNAc ; and the use of sustained-released preparations of free sialic acid. In addition, the finding that 6'-sialyllactose and peracetylated ManNAc remarkably increased sialic acid level in kidney also suggest that the other diseases associated with GNE gene mutation, such as severe renal disorders in Gne mutants (Galeano et al, 2007;Ito et al, 2012) and other transgenic models (Clement et al, 2011), would be treatable strategies.…”

New insights into the role of Jmjd3 and Utx in axial skeletal formation in mice

“…Samples were lysed in radio immunoprecipitation assay buffer (25 mM Tris‐HCl, pH 7.6, 150 mM NaCl, 1% NP‐40, 1% sodium deoxycholate, 0.1% SDS), and were boiled at 99°C for 3 min after adding Laemmli's sample buffer. SDS‐PAGE and Western blotting were performed as previously described (43).…”