Investigating Genetic Polymorphisms in Heparan Sulfate Proteoglycans and MS Susceptibility

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease affecting the central nervous system (CNS) in young adults. This complex disease is characterized by polygenic heritable components and multifaceted gene-environment interactions. Heparan sulfate proteoglycans (HSPGs), which are ubiquitous to the cell surface and the extracellular matrix, have been implicated in numerous cellular processes. HSPG biosynthesis is a complex process involving the enzymatic attachment of heparan sulfate (HS) chains to a core protein, mediating specific ligand and growth factor interactions that direct cellular processes such as adhesion, migration, and differentiation. This study investigates genetic polymorphisms in HSPGs and key modification enzymes in an Australian Caucasian MS population to further understand their role in disease susceptibility.

Two main families of HSPGs exist: syndecans (SDC1-4) and glypicans (GPC1-6). Syndecans are transmembrane proteins, while glypicans are glycosylphosphatidylinositol (GPI)-linked to the cell surface. Genome-wide association studies (GWAS) have identified regions of the genome associated with MS, including chromosome 13, which contains GPC5 and GPC6. This study focuses on replicating and extending previous findings related to these genes in an Australian case-control population.

The study utilized a Caucasian case-control population of 205 MS patient samples and 194 age- and sex-matched control samples. The case samples were divided into relapsing-remitting (RRMS), secondary progressive (SPMS), and primary progressive (PPMS) MS subtypes. Genomic DNA was extracted from peripheral blood, quantified, and quality-checked before analysis.

Primers for EXT1, SULF1, and SDC1 were designed for use in polymerase chain reaction (PCR) and subsequent analysis. GPC5 and GPC6 SNPs were analyzed using high-resolution melt (HRM) analysis and pyrosequencing. Statistical analyses included Hardy-Weinberg equilibrium (HWE), chi-square tests, and multiple testing corrections using the Benjamini-Hochberg and Bonferroni methods.

Modification Enzymes
EXT1 and SULF1: No significant associations were found between EXT1 rs11546829 or SULF1 rs2623047 SNPs and MS susceptibility in the total or stratified populations.

Core Proteins SDC1 (rs1131351): A significant association was identified between the SDC1 SNP and MS, particularly in females with primary progressive or relapsing-remitting MS. The minor allele was associated with increased risk, suggesting a role for SDC1 in disease initiation.

GPC5 (rs10492503): Significant associations were observed between GPC5 rs10492503 and MS, particularly in secondary progressive and relapsing-remitting MS subtypes, and in the female population. This SNP was associated with increased disease risk.

GPC6 (rs17267815): A minor significant association was identified between GPC6 rs17267815 and relapsing-remitting MS, particularly in males. This SNP was associated with the early-onset form of the disease.

The findings suggest a significant role for SDC1, GPC5, and GPC6 polymorphisms in MS susceptibility. The lack of significant associations for EXT1 and SULF1 does not rule out their potential involvement, as further investigation with larger cohorts is warranted. The study highlights the complex interplay between genetic factors and disease progression, supporting the involvement of these genes in MS development and progression.

Conclusion
This study provides evidence for the involvement of HSPG core proteins SDC1, GPC5, and GPC6 in MS susceptibility within an Australian Caucasian population. The associations observed, particularly in specific MS subtypes and in females, underscore the importance of these genetic polymorphisms in understanding MS pathogenesis and developing potential therapeutic targets.

References:
Okolicsanyi, R.K., Bluhm, J., Miller, C., Griffiths, L.R., & Haupt, L.M. (2020). An investigation of genetic polymorphisms in heparan sulfate proteoglycan core proteins and key modification enzymes in an Australian Caucasian multiple sclerosis population. Human Genomics, 14(18).