Role of PTPN2/22 polymorphisms in pathophysiology of Crohn's disease

Abstract

Aim: To establish the relationship of protein tyrosine phosphatase non-receptor type 2 and 22 (PTPN2/22) polymorphisms and mycobacterial infections in Crohn's disease (CD).

Methods: All 133 subjects' blood samples were genotyped for nine single nucleotide polymorphisms (SNPs) in PTPN2/22 using TaqMan™ genotyping, while the effect of the SNPs on PTPN2/22 and IFN-γ gene expression was determined using RT-PCR. Detection of Mycobacterium avium subspecies paratuberculosis (MAP) IS900 gene was done by nPCR after DNA extraction from the isolated leukocytes of each subjects' blood samples. T-cells isolated from the patient samples were tested for response to phytohematoagglutonin (PHA) mitogen or mycobacterial antigens by BrdU proliferation assays for T-cell activity.

Results: Out of the nine SNPs examined, subjects with either heterozygous (TC)/minor (CC) alleles in PTPN2:rs478582 occurred in 83% of CD subjects compared to 61% healthy controls (P-values < 0.05; OR = 3.03). Subjects with either heterozygous (GA)/minor (AA) alleles in PTPN22:rs2476601 occurred in 16% of CD compared to 6% healthy controls (OR = 2.7). Gene expression in PTPN2/22 in CD subjects was significantly decreased by 2 folds compared to healthy controls (P-values < 0.05). IFN-γ expression levels were found to be significantly increased by approxiately 2 folds in subjects when either heterozygous or minor alleles in PTPN2:rs478582 and/or PTPN22:rs2476601 were found (P-values < 0.05). MAP DNA was detected in 61% of CD compared to only 8% of healthy controls (P-values < 0.05, OR = 17.52), where subjects with either heterozygous or minor alleles in PTPN2:rs478582 and/or PTPN22:rs2476601 had more MAPbacteremia presence than subjects without SNPs did. The average T-cell proliferation in CD treated with PHA or mycobacteria antigens was, respectively, 1.3 folds and 1.5 folds higher than healthy controls without any significant SNP.

Conclusion: The data suggests that SNPs in PTPN2/22 affect the negative regulation of the immune response in CD patients, thus leading to an increase in inflammation/apoptosis and susceptibility of mycobacteria.

Keywords: Crohn’s disease; Mycobacteria; PTPN2; PTPN2/22; PTPN22; Single nucleotide polymorphisms.

Figure 1

Shared genetic predispositions and environmental triggers between common inflammatory autoimmune disorders. For inflammatory autoimmune disorders, many share the same treatments and some of the same genetic single nucleotide polymorphisms in specific immunity genes. Thus, it is possible that these disorders share the same environmental triggers as well, such as Mycobacterium avium subspecies paratuberculosis (MAP) bacterial infection. CD: Crohn’s disease; PTPN2: Protein tyrosine phosphatase non-receptor type 2; PTPN22: Protein tyrosine phosphatase non-receptor type 22.

Figure 2

Allele frequency in nine single nucleotide polymorphisms in crohn’s disease and healthy control subjects. A: Represents allele frequency of PTPN2 SNPs: rs1893217, rs2542151, rs7234029, rs478582; B: Represents allele frequency of PTPN22 SNPs: rs2476601, rs2488457, rs33996649, rs34209542, rs2476599; C: Represents haplotype combinations PTPN2:rs478582 and PTPN22:rs2476601. ^aP < 0.05, healthy vs CD. T-G: Major/major; C-G: SNP/major; T-A: Major/SNP; C-A: SNP/SNP; SNPs: Single nucleotide polymorphisms; CD: Crohn’s disease; PTPN2: Protein tyrosine phosphatase non-receptor type 2; PTPN22: Protein tyrosine phosphatase non-receptor type 22.

Figure 3

Relative mRNA expression (2(^-∆CT) × 1000) of PTPN2, PTPN22 and IFN-γ. Relative mRNA expression of PTPN2 (A) and PTPN22 (B) in CD and healthy control subjects. Relative mRNA expression of IFN-γ was correlated with CD and healthy control subjects with either PTPN2:rs478582 (C) or PTPN22:2476601 (D). IFN-γ: Interferon-γ; CD: Crohn’s disease; PTPN2: Protein tyrosine phosphatase non-receptor type 2; PTPN22: Protein tyrosine phosphatase non-receptor type 22. ^aP < 0.05.

Figure 4

The effect of both Mycobacterium avium subspecies paratuberculosis and PTPN2:rs478582 on IFN-γ gene expression in Crohn’s disease and healthy control subjects. IFN-γ: Interferon-γ; CD: Crohn’s disease; MAP: Mycobacterium avium subspecies paratuberculosis; SNPs: Single nucleotide polymorphisms.

Figure 5

Complex interaction of Crohn’s disease pathophysiology. The effect of single nucleotide polymorphisms (SNPs) in Protein tyrosine phosphatase non-receptor type 2 and 22 (PTPN2/22) and Mycobacterium avium subspecies paratuberculosis (MAP) in a dysregulated immune response in crohn’s disease (CD).