Lipase-a single-nucleotide polymorphism rs143793106 is associated with increased risk of aggressive periodontitis by negative influence on the cytodifferentiation of human periodontal ligament cells

Background and objective: Aggressive periodontitis (AgP) is characterized by general health and rapid destruction of periodontal tissue. The familial aggregation of this disease highlights the involvement of genetic factors in its pathogeny. We conducted a genome-wide association study (GWAS) to identify AgP-related genes in a Japanese population, and the lipid metabolism-related gene, lipase-a, lysosomal acid type (LIPA), was suggested as an AgP candidate gene. However, there is no report about the expression and function(s) of LIPA in periodontal tissue. Hence, we studied the involvement of how LIPA and its single-nucleotide polymorphism (SNP) rs143793106 in AgP by functional analyses of LIPA and its SNP in human periodontal ligament (HPDL) cells.

Materials and methods: GWAS was performed using the genome database of Japanese AgP patients, and the GWAS result was confirmed using Sanger sequencing. We examined the mRNA expression level of LIPA and the protein expression level of the encoded protein lysosomal acid lipase (LAL) in periodontium-composing cells using conventional and real-time polymerase chain reaction (PCR) and western blotting, respectively. Lentiviral vectors expressing LIPA wild-type (LIPA WT) and LIPA SNP rs143793106 (LIPA mut) were transfected into HPDL cells. Western blotting was performed to confirm the transfection. LAL activity of transfected HPDL cells was determined using the lysosomal acid lipase activity assay. Transfected HPDL cells were cultured in mineralization medium. During the cytodifferentiation of transfected HPDL cells, mRNA expression of calcification-related genes, alkaline phosphatase (ALPase) activity and calcified nodule formation were assessed using real-time PCR, ALPase assay, and alizarin red staining, respectively.

Results: The GWAS study identified 11 AgP-related candidate genes, including LIPA SNP rs143793106. The minor allele frequency of LIPA SNP rs143793106 in AgP patients was higher than that in healthy subjects. LIPA mRNA and LAL protein were expressed in HPDL cells; furthermore, they upregulated the cytodifferentiation of HPDL cells. LAL activity was lower in LIPA SNP-transfected HPDL cells during cytodifferentiation than that in LIPA WT-transfected HPDL cells. In addition, ALPase activity, calcified nodule formation, and calcification-related gene expression levels were lower during cytodifferentiation in LIPA SNP-transfected HPDL cells than those in LIPA WT-transfected HPDL cells.

Conclusion: LIPA, identified as an AgP-related gene in a Japanese population, is expressed in HPDL cells and is involved in regulating cytodifferentiation of HPDL cells. LIPA SNP rs143793106 suppressed cytodifferentiation of HPDL cells by decreasing LAL activity, thereby contributing to the development of AgP.