The Gne M712T Mouse as a Model for Human Glomerulopathy

Abstract

Pathological glomerular hyposialylation has been implicated in certain unexplained glomerulopathies, including minimal change nephrosis, membranous glomerulonephritis, and IgA nephropathy. We studied our previously established mouse model carrying a homozygous mutation in the key enzyme of sialic acid biosynthesis, N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase. Mutant mice died before postnatal day 3 (P3) from severe glomerulopathy with podocyte effacement and segmental glomerular basement membrane splitting due to hyposialylation. Administration of the sialic acid precursor N-acetylmannosamine (ManNAc) led to improved sialylation and survival of mutant pups beyond P3. We determined the onset of the glomerulopathy in the embryonic stage. A lectin panel, distinguishing normally sialylated from hyposialylated glycans, used WGA, SNA, PNA, Jacalin, HPA, and VVA, indicating glomerular hyposialylation of predominantly O-linked glycoproteins in mutant mice. The glomerular glycoproteins nephrin and podocalyxin were hyposialylated in this unique murine model. ManNAc treatment appeared to ameliorate the hyposialylation status of mutant mice, indicated by a lectin histochemistry pattern similar to that of wild-type mice, with improved sialylation of both nephrin and podocalyxin, as well as reduced albuminuria compared with untreated mutant mice. These findings suggest application of our lectin panel for categorizing human kidney specimens based on glomerular sialylation status. Moreover, the partial restoration of glomerular architecture in ManNAc-treated mice highlights ManNAc as a potential treatment for humans affected with disorders of glomerular hyposialylation.

Mucin-type O-Glycosylation during Development

“…Hyposialylated O-glycoproteins present in the developing kidneys of these mice included podocalyxin and nephrin. Interestingly, dietary supplementation with N-acetylmannosamine, a sialic acid precursor that bypasses the Gne M712T mutation, partially restored O-glycan sialylation, podocyte structure, and renal function (42). Taken together, these findings support the proposal that negatively charged sialic acids on O-linked glycoproteins (such as podocalyxin) in the developing kidneys are necessary for proper repulsion of adjacent podocyte foot processes to form functional filtration slits.…”

“…It was proposed that O-glycosylation of podocalyxin, a sialylated O-glycoprotein present on the renal podocyte foot process, may be necessary for proper filtration slit formation and renal function, as mice deficient for podocalyxin (podx1 Ϫ/Ϫ ) also displayed similar kidney defects (61). This hypothesis was further supported by recent studies examining mice mutant for an enzyme involved in sialic acid biosynthesis, N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE/ MNK), which is encoded by the Gne gene (42). Mice homozygous for the Gne M712T/M712T mutation displayed loss of sialylated O-glycans in the developing kidneys, podocyte effacement, and death from renal failure by postnatal day 3 (Table 1).…”

Large-Scale Identification of N-Glycan Glycoproteins Carrying Lewis x and Site-Specific N-Glycan Alterations in Fut9 Knockout Mice

“…[30][31][32][33] In WT kidney, glomeruli are strongly stained while other areas are not stained by Sambucus nigra agglutinin (SNA) during lectin staining. 34,35 As shown in Figure 2a in this study, the percentage of sialylated N-glycans was very low. This might correlate with the low occupancy of glomeruli in the kidney.…”

DNA hypermethylation and DNA hypomethylation is present at different loci in chronic kidney disease

“…Top-ranked genes have been reported with roles in disease, regulation, signaling, and apoptotic pathways, however formal Partek pathway analysis identified only three pathways with P < 0.05; top-ranked was mucin type O-glycan biosynthesis (P = 0.02) and it is of note that mucin-type O-glycosylation is important for kidney development with abnormalities associated with renal dysfunction, abnormal glomeruli, proximal tubules, and renal podocytes. [39][40][41] Enrichment based on gene ontology also highlighted O-glycosylation with the most significant results being for biological processes protein O-linked glycosylation via serine (P = 0.002, GO ID = 18 242) and protein O-linked glycosylation via threonine (P = 0.002, GO ID = 18 243). Analysis of the interaction profile did not reveal anything of note.…”