Integrating glycomics and genomics uncovers SLC10A7 as essential factor for bone mineralization by regulating post-Golgi protein transport and glycosylation

Abstract

Genomics methodologies have significantly improved elucidation of Mendelian disorders. The combination with high-throughput functional-omics technologies potentiates the identification and confirmation of causative genetic variants, especially in singleton families of recessive inheritance. In a cohort of 99 individuals with abnormal Golgi glycosylation, 47 of which being unsolved, glycomics profiling was performed of total plasma glycoproteins. Combination with whole-exome sequencing in 31 cases revealed a known genetic defect in 15 individuals. To identify additional genetic factors, hierarchical clustering of the plasma glycomics data was done, which indicated a subgroup of four patients that shared a unique glycomics signature of hybrid type N-glycans. In two siblings, compound heterozygous mutations were found in SLC10A7, a gene of unknown function in human. These included a missense mutation that disrupted transmembrane domain 4 and a mutation in a splice acceptor site resulting in skipping of exon 9. The two other individuals showed a complete loss of SLC10A7 mRNA. The patients' phenotype consisted of amelogenesis imperfecta, skeletal dysplasia, and decreased bone mineral density compatible with osteoporosis. The patients' phenotype was mirrored in SLC10A7 deficient zebrafish. Furthermore, alizarin red staining of calcium deposits in zebrafish morphants showed a strong reduction in bone mineralization. Cell biology studies in fibroblasts of affected individuals showed intracellular mislocalization of glycoproteins and a defect in post-Golgi transport of glycoproteins to the cell membrane. In contrast to yeast, human SLC10A7 localized to the Golgi. Our combined data indicate an important role for SLC10A7 in bone mineralization and transport of glycoproteins to the extracellular matrix.

A mutation in mannose‐phosphate‐dolichol utilization defect 1 reveals clinical symptoms of congenital disorders of glycosylation type I and dystroglycanopathy

“…Serum transferrin isoelectric focusing (TIEF) and electrospray ionization mass spectrometry (ESI‐MS) were performed as described . Whole exome sequencing (WES), high‐performance liquid chromatography (HPLC), and thin‐layer chromatography (TLC) of LLOs and DPM were performed as described elsewhere …”

“…[10][11][12] Whole exome sequencing (WES), high-performance liquid chromatography (HPLC), and thin-layer chromatography (TLC) of LLOs and DPM were performed as described elsewhere. 13,14…”

Bone and connective tissue disorders caused by defects in glycosaminoglycan biosynthesis: a panoramic view

“…The same findings have been reported in cartilage from a Cant1 knock‐out mouse; however, ER enlargement does not trigger ER stress and conventional unfolded protein response (UPR) despite reduced PG secretion . Lastly, confocal microscopy in skin fibroblasts from patients with mutations in SLC10A7 has demonstrated enlargement of the Golgi due to post‐Golgi transport defects through the secretory pathway .…”

“…A clinical entity characterized by amelogenesis imperfecta, severe pre-and postnatal disproportionate short stature, congenital dislocations and advanced carpal and tarsal ossifications has been described recently [100]. The disorder is caused by mutations in the SLC10A7 gene encoding for a 10-transmembrane domain transporter whose specific function and substrate remain unknown [100,101]. Total GAG content in patients' fibroblasts and in cartilage from a Slc10a7 knock-out mouse is normal, but a low amount of HS and a correspondingly increase in CS has been described suggesting the involvement of this transporter in PG biosynthesis [100].…”

“…Total GAG content in patients' fibroblasts and in cartilage from a Slc10a7 knock-out mouse is normal, but a low amount of HS and a correspondingly increase in CS has been described suggesting the involvement of this transporter in PG biosynthesis [100]. Immunofluorescence studies in transfected cells have localized the protein in the Golgi network and a defective post-Golgi transport of glycoproteins through the secretory pathway has been described in patients' fibroblasts [101]. Moreover, studies in Slc10a7 yeast homologues and in cells transfected with expression plasmids for the SLC10A7 have localized the transporter in the plasma membrane suggesting a possible role as a negative regulator of cytosolic calcium homoeostasis [100,102,103].…”