Identification of two variants of the human integrin alpha 4 subunit

Integrin adhesion in brain assembly: From molecular structure to neuropsychiatric disorders

Integrins are extracellular matrix receptors that mediate biochemical and mechanical bi-directional signals between the extracellular and intracellular environment of a cell thanks to allosteric conformational changes. In the brain, they are found in both neurons and glial cells, where they play essential roles in several aspects of brain development and function, such as cell migration, axon guidance, synaptogenesis, synaptic plasticity and neuro-inflammation. Although there are many successful examples of how regulating integrin adhesion and signaling can be used for therapeutic purposes, for example for halting tumor progression, this is not the case for the brain, where the growing evidence of the importance of integrins for brain pathophysiology has not translated yet into medical applications. Here, we review recent literature showing how alterations in integrin structure, expression and signaling may be involved in the etiology of autism spectrum disorder, epilepsy, schizophrenia, addiction, depression and Alzheimer's disease. We focus on common mechanisms and recurrent signaling pathways, trying to bridge studies on the genetics and molecular structure of integrins with those on synaptic physiology and brain pathology. Further, we discuss integrin-targeting strategies and their potential benefits for therapeutic purposes in neuropsychiatric disorders.

A Novel Association of Polymorphism in the ITGA4 Gene Encoding the VLA-4 α4 Subunit with Increased Risk of Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent cause of dementia in elderly people worldwide. Many studies support the hypothesis that the inflammation of the CNS contributes to the neurodegeneration and disease progression. The integrin molecule α4β1, also known as very late antigen 4 (VLA-4), belongs to adhesion molecules that activate the inflammatory process through the migration of immune cells into the CNS. Therefore, the objective of our study was to analyze the association between two polymorphisms located in the ITGA4 gene encoding the α4 subunit of VLA-4 and the risk of AD. 104 late-onset AD patients and 206 control subjects from Slovakia were genotyped for ITGA4 gene SNP polymorphism rs113276800 (-269C/A) and rs1143676 (+3061A/G). The same study cohorts were also genotyped for the APOE-ε4, which is a known genetic factor associated with increased risk of AD developing. ITGA4 polymorphism analysis revealed significantly higher frequency of the +3061AG carriers in AD group compared to the controls (P ≤ 0.05). Following the APOE-ε4 stratification of study groups, the association remained significant only in APOE-ε4 noncarriers. Our study suggests a novel association of ITGA4 +3061A/G polymorphism with AD and its possible contribution to the disease pathology.

VLA4 Gene Polymorphism and Susceptibility to Multiple Sclerosis in Slovaks

Multiple sclerosis (MS) is an inflammatory autoimmune disease occurring in genetically sensitive individuals. As migration of immune cells into the CNS is facilitated by the Very Late Antigen 4 (VLA-4) integrin molecule, the VLA4 gene may be considered as a plausible candidate genetic risk factor for susceptibility to MS. Therefore, the objective of our study was to investigate the association between two genetic polymorphisms located in the VLA4 gene and the risk of multiple sclerosis. One hundred seventeen MS patients and 165 control subjects from Slovakia were genotyped for VLA4 gene SNP polymorphisms at positions 269 (C/A) and 3061 (A/G). The same study cohorts were also genotyped for the rs3135388 polymorphism tagging the HLA-DRB1*15:01 allele, which is a known genetic factor associated with susceptibility to develop MS in many populations. Our findings show for the first time that the rs3135388 polymorphism is a strong risk factor for MS in the Slovak population. Investigation of the VLA4 gene polymorphisms revealed a significantly higher frequency of the 3061AG genotype in MS patients compared to the controls (P ≤ 0.05). We suggest that the 3061AG polymorphic variant is an independent genetic risk factor for MS development in our population as it was significantly associated with this disease. The association was also confirmed after applying multivariate logistic-regression analysis adjusted for gender, age and HLA-DRB1*15:01 positivity as possible influencing factors.

Frequencies of alpha4 A3061G variants and identification of three new variants of the human integrin alpha4-subunit

Human integrin alpha4beta1 (VLA-4) is thought to play a key role in immune responses. Only two variants of alpha4-subunit (alpha4-tex and alpha4-mas) have been described until now, and the information regarding these variants is scanty. In this study, we measured the frequency of both variants in healthy blood donors (n=252). Surprisingly, the frequency of alpha4-mas (3061G, 0.31) was lower than that of alpha4-tex (3061A, 0.69). In addition, we sequenced and analyzed the mRNA of the entire alpha4-subunit in eight unselected healthy blood donors. These studies revealed three new variants, including a C to A transversion at position 269 in the promoter region of exon 1 (accession no. AJ504733); a G to A transversion at position 2273 in exon 16 (accession no. AJ510246, AJ510247), and a T to C exchange at position 3311 in exon 26 (accession no. AJ510248, AJ510249). None of these variants led to amino acid (AA) substitutions. Interestingly, homozygosity of the new variant 269A was not found.

Expression of a soluble functional form of the integrin alpha4beta1 in mammalian cells

The integrin alpha4beta1(VLA4) has been expressed as a soluble, active, heterodimeric immunoglobulin fusion protein. cDNAs encoding the extracellular domains of the human alpha4 and beta1 subunits were fused to the genomic DNA encoding the human gamma1 immunoglobulin Fc domain and functional integrin fusion protein was expressed as a secreted, soluble molecule from a range of mammalian cell lines. Specific mutations were introduced into the Fc region of the molecules to promote alpha4beta1 heterodimer formation. The soluble alpha4beta1-Fc fusion protein exhibited divalent cation dependent binding to VCAM-1, which was blocked by the appropriate function blocking antibodies. The apparent Kd for VCAM-1 binding were similar for both the soluble and native forms of alpha4beta1. In addition, the integrin-Fc fusion was shown to stain cells expressing VCAM-1 on their surface by FACs analysis. This approach for expressing soluble alpha4beta1 should be generally applicable to a range of integrins.