The Study On Single Nucleotide Polymorphism In PAF-AH Gene Of Patients With Psoriasis

Platelet-activating factor (PAF)¹ is a biologically active phospholipid with diverse potent biological effects. PAF has been implicated as a mediator of physiological processes such as signaling and activation of proinflammatory cells, alteration of vascular permeability, and stimulation of glycogen metabolism. In addition to its role as a physiological mediator, PAF is associated with the pathology of several human diseases, particularly allergy and inflammation, affecting the respiratory, vascular, digestive and reproductive systems. PAF exerts its actions at concentrations as low as 10^-12 M. Its accumulation is tightly regulated at the synthetic and degradative levels to avoid the inappropriately high accumulation of PAF observed in many diseases.PAF is degraded to inactive products by hydrolysis of the acetyl group at the sn-2 position, to produce the biologically inactive products lyso-PAF and acetate. PAF is degraded to inactive products by hydrolysis of the acetyl group at the sn -2 position, to produce the biologically inactive products lyso-PAF and acetate. This reaction is catalyzed by PAF acetylhydrolase, a calcium-independent phospholipase A 2 specific for hydrolysis of phospholipids containing short and/or oxidized chains at the sn -2 position of the glycerol backbone. There are 2 type of PAF-AH, namely plasma PAF-AH and cellular PAF-AH . The latter have 3 isoenzyme:type I a, type I b and type â…¡. The β subunit is 99% homologous to a product of the LIS1 gene, mutations of which cause type I lissencephaly.The gene for the plasmatic PAF-AH has been mapped to chromosome 6p21.2-pl2, consisting of 12 exons, originally assigned as the human leukocyte antigen region. The predicted amino acid sequence of the plasma form of PAF acetylhydrolase contains a Gly-Xaa-Ser- Xaa-Gly motif characteristic of lipases and esterases. The serine residue in this conserved motif is essential for activity and it explains the ability of serine esterase inhibitors to abolish enzymatic activity. Miwa et al.] first reported that the deficiency of plasma PAF-AH activity was transmitted by autosomalrecessive heredity in five Japanese families. Most instances are due to aloss-of-function mutation (Val279Phe, exon 9, position 994; G---J) in the plasmaPAF-AH gene]. Val-279 is conserved in plasma PAF-AH from different species and this amino acid lies between the active site Ser-273 and Asp-296 residues in a region that is critical for proper folding of the enzyme. The incidence of the mutation is reported to be high in healthy Japanese with heterozygous and homozygous frequencies of 27 and 4%, respectively]. Although this mutation has previously only been reported exclusively in the Japanese population, this mutation was reported in Kirghiz and Turkish populations also. Considering the fact that the Turkish and Japanese population claim Asiatic origin going back to thousands of years, this mutation is probably originated from central Asia and was introduced to Japan and Turkey through population movements. Another loss-of-function mutation (Gln281Arg, exon 9, position 1001, A——?*G) is also found in the Japanese population. Other gene variants, Arg92His(exon 4, position 275; G---?A), Ilel98Thr (exon 7, position 593; T—?C), Ala379Val(exon 11, position 1136, T---?C) are described in white populations. The variantsAla379Val and Ilel98Thr show increased Km values (14 and 42 ^M, respectively) when compared with the wild type (7 PM), although the Vmax values of these two variants remain constant. Therefore, these two variants are very likely to prolong the activities of PAF in the plasma. Ilel98Thr is located near Tyr-205, which is proposed to be important for LDL binding. Since the LDL-associated form of PAF-AH is responsible for the PAF hydrolysis, this variant may alter LDL binding and consequently influence PAF degradation. Ala379Val is situated in the vicinity of His-351, one of the amino acids belonging to the catalytic triad of the lipase, so this variant may influence enzyme activities. The study we have done before shows that some variants of PAF-AH gene do not influence enzyme activities. Some point mutations may be not a genetic risk factor for psoriasis.PAF or PAF-AH plays a key role in the pathogenesis of psoriasis which is a common skin disease.It is important for the prophylaxis and therapy to identify the correlation between PAF-AH and psoriasis in Chinese.PART 1 The study on SNP in Platelet-activating factor acetylhydrolase gene exon 4 G/A(Position 275) in the health group of the Han nationality in ShangHai region.Objective: To investigate the distributing of SNP in PAF-AH gene exon 4 G/A(Position 275) in the health group of the Han nationality in ShangHai region and the character compared with different races.Methods: Genomic DNA was analyzed for the mutation allele in 100 healthy controls by the polymerase -chain reaction and restriction fragement-length polymorphism. Then the prevalence of the mutation and the frequency of the mutation was calculated and compared with various races.Result: The frequency of GG genotype is the highest in the health group of the Han nationality in ShangHai region and then GA . There is no AA. The prevalence of the mutation of GG and GA is 88% and 12%. The frequency of the mutation of G in the health group of the Han nationality in ShangHai region is higher than that of the Britain.Conclusion: The frequency of the mutation of G-*-A in the health group of the Han nationality in ShangHai region is low. There is significant difference comparing with those in Britain.PART 2 Association of Arg92His missense mutation in the Platelet-activating factor acetylhydrolase gene with genetic susceptibility to psoriasis.Objective: To investigate the correlation between the mutation of platelet-activating factor(PAF) acetylhydrolase and psoriasis.Methods: Genomic DNA was analyzed for the mutation allele in 47 patients with psoriasis and 52 healthy controls by the polymerase -chain reaction and restriction fragement-length polymorphism.Result: The prevalence of the mutation and the frequency of the mutation in 47 patient with psoriasis have significant difference with those in 52 health control . The frequency of the mutation of PAF-AH gene in psoriasis is higher than that in controls.Conclusion: The rate of mutation of platelet-activating factor(PAF) acetylhydrolase is related with psoriasis, the mutation may be a genetic risk factor for psoriasis..PART 3 Association of Ilel98Thr missense mutation in the Platelet-activating factor acetylhydrolase gene with genetic susceptibility to psoriasis.Objective: To investigate the correlation between the mutation of platelet-activating factor(PAF) acetylhydrolase and psoriasis.Methods: Genomic DNA was analyzed for the mutation allele in50 patients with psoriasis and 50 healthy controls by the polymerase-chain reaction and sequencing.Result: The prevalence of the mutation and the frequency of the mutation in 50 patients with psoriasis have no significant difference with those in 50 health control .The amplification product is 240bp. There are two genotypes:TT and TC. 44 is TT and 6 is TC of 50 health control. While 45 is TT and 5 is TC of 50 patients with psoriasis .Conclusion: The rate of mutation of platelet-activating factor (PAF) acetylhydrolase is no related with psoriasis, the mutation may be not a genetic risk factor for psoriasis.PART 4 Association of Ala379Val missense mutation in the Platelet-activating factor acetylhydrolase gene with genetic susceptibility to psoriasis.Objective: To investigate the correlation between the mutation of platelet-activating factor(PAF) acetylhydrolase and psoriasis.Methods: Genomic DNA was analyzed for the mutation allele in 60 patients with psoriasis and 60 healthy controls by the polymerase-chain reaction and sequencing.Result: The prevalence of the mutation and the frequency of the mutation in 60patients with psoriasis have no significant difference with those in 60 health control .The amplification product is 320bp. There are three genotypes:TT TC and CC. 6 is TT and 9 is TC and 45 is CC of 60 health control.While 5 is TT and 15 is TC and 40 is CC of 60 patients with psoriasis.