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Abstract

CD40 signaling is a key modulator of immunological responses and serves several biological functions across multiple organs. While its primary purpose is restoring homeostasis, its unregulated activation drives various immune-modulated pathological conditions. Its role in the development of insulin resistance and the progression of diabetes is well documented. A further contribution of CD40 signaling in escalating systemic inflammation in diabetes leads to the initiation of vascular complications. The functional single nucleotide polymorphism (SNP) in the Kozak region of the CD40 gene (T-1C, rs1883832) impacts CD40 translation efficiency and is associated with several immune and inflammation-modulated diseases. Given the role of CD40 signaling in the progression of diabetes and systemic inflammation, this SNP may also represent a genetic risk factor for diabetes. This hypothesis was investigated by examining the distribution of the T-1C SNP in patients with type 1 (T1D) and type 2 diabetes (T2D). There was, in fact, a strong association of the C-allele with T2D (odds ratio = 1.43; 95% confidence interval: 1.09-1.86). T2D patients also revealed higher plasma levels of the presumably protective soluble CD40 receptor (sCD40), which is known to neutralize the CD40 ligand (CD40L) and its pro-inflammatory capacity. Hence, in T2D patients, CD40 signaling seems to be switched on, leading to an upregulation of the compensatory sCD40 in the blood. The possibility that the T-1C SNP differentially affects the genome of sCD40L-stimulated CC and TT-genotype human cultured endothelial cells (HUVECs) was examined through RNA sequencing. The CC-genotype HUVECs exhibited a higher degree of gene expression in general and in particular of genes involved in escalating inflammation, insulin receptor recycling, and driving endothelial to mesenchymal transition (EndMT). The quiescent TT-genotype HUVECs seemed to be protected against such changes. The impact of a pro-diabetic microenvironment on the pro-inflammatory CC-genotype HUVECs was further studied. Under these conditions, they revealed an increased expression of mediators promoting inflammation, atherosclerosis, and EndMT. In addition, they showed morphological changes characteristic of a partial EndMT-like phenotype. Expression of the osmoadaptive transcription factor nuclear factor of activated T-cells (NFAT) 5 and its nuclear abundance was also increased under these conditions. Blocking NFAT5 DNA-binding in the CC-genotype HUVECs by using a neutralizing consensus NFAT5 decoy oligonucleotide significantly reduced the expression of the mesenchymal marker SM22α. Several nuclear factor κB (NF-κB)/NFAT5 dual binding sites are located in promotor regions of genes involved in the progression of atherosclerosis and EndMT. While NF-κB is known to drive inflammation and EndMT in HUVECs, less is known about the role of NFAT5 in modulating these processes. This work provides novel insights into the role of NFAT5 in enhancing NF-κB mediated vascular inflammation and EndMT under pro-diabetic conditions.