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  • Optineurin was first identified by Li

    2019-07-30

    Optineurin was first identified by Li′s group [1] using a yeast two-hybrid system and named FIP-2 - interacting protein of Adenovirus E3 14.7-kDa protein. Later, in 2002, mutations in this gene were found to be associated with primary open-angle glaucoma, a disease that causes irreversible bilateral blindness, and the gene was renamed “optineurin” (OPTN) [2]. The human OPTN gene is located in the short arm of chromosome 10 (13099449–13138308) and spans about 39 Mbp of genomic DNA. It contains three noncoding exons in the 5′ untranslated region (UTR) and 13 exons that code for a 577 amino L-NAME hydrochloride protein. Alternative splicing in the 5′ UTR generates at least four different transcripts (NM_001008211.1, NM_001008212.1, NM_001008213.1, and NM_021980), but all have the same open reading frame. Alternative splicing in the coding region give rise to three different protein isoforms with 571 (ENST00000378764), 126 (ENST00000424614) and 107 (ENST00000486862) amino acids. Also, two partial transcripts were also described, but there is no indication of being protein coding. In addition, in 2012 a ‘new first exon’ was described, upstream from the previously known exon 1, and was labelled as exon 1a [3]. The OPTN protein consists of a NEMO-like domain, a leucine zipper motif, multiple coiled-coil motifs, an ubiquitin binding domain (UBD), a L-NAME hydrochloride microtubule associated protein 1 light chain 3 (LC3)-interacting motif, and a C-terminal zinc finger [4]. OPTN is known to undergo posttranslational modifications and after being ubiquitinated it is processed through the ubiquitin-proteasome pathway [5]. It is also phosphorylated at Ser177, which is adjacent to the LC3 interacting region (LIR) site [6]. OPTN is a multifunctional protein involved in several biological functions such as NF-κB regulation, autophagy, membrane trafficking, exocytosis, vesicle transport, transcriptional activation, and reorganizing of actin and microtubules, since it interacts with several proteins, including Rab8, huntingtin, transcription factor IIIA, myosin VI, and TANK binding protein 1 (TBK1). OPTN biological role is not yet fully understood and appears to be complex and involve different mechanisms and pathways (reviewed in [7]). Besides glaucoma, a number of diseases such as neurodegenerative diseases (like Alzheimer's disease, Parkinson's disease [8] and amyotrophic lateral sclerosis [9]) and Paget's disease of bone (PDB) [3], [10] have been associated with mutations in OPTN. PDB is the second most frequent metabolic bone disorder, after osteoporosis [11], affecting between 1% and 3% of individuals over the age of 55years [12], [13]. This disease is characterized by focal abnormal bone remodelling, with increased bone resorption and accelerated, excessive, and disorganized new bone formation. The pathophysiology of PDB is currently an area of intensive investigation, and this disease seems to have both genetic and non-genetic causes. Fifteen to 40% of affected patients have a first-degree relative with PDB, and numerous studies have described extended families with PDB exhibiting an autosomal dominant mode of inheritance [14], [15], [16]. Linkage studies in these families have identified a number of susceptibility loci on chromosomes 6p21 (PDB1) [17], 18q21.1–22 (PDB2) [18], 5q35 (PDB3), 5q31 (PDB4) [15], 2q36 (PDB5) [19], 10p13 (PDB6) [20] and 18q23 (PDB7) [19]. The regions identified are typically large and contain several genes that could be possible candidates based on their known functions. Moreover, a genome-wide scan in British families with PDB has shown a linkage to the 10p13 (PDB6) locus [20], [21]. Recently, reanalysis of data from this genome-wide scan confirmed a genetic association to the 10p13 locus [10], namely to the rs1561570 SNP located in OPTN gene, but no PDB causal mutation has been reported to date in this locus. Our group replicated the strong and statistically significant genetic association of rs1561570 (p-value=5.65×10) with PDB in the French-Canadian population [3], and also identified a functional SNP in UCMA/GRP, but with a marginal association with PDB, and a rare variant in OPTN promoter predicted to alter the putative binding of bone transcription factors [3]. In this work, we have assessed the possible contribution of each significant variant identified in the OPTN gene and have selected rs3829923 and rs2234968 to perform the association study and functional analysis in order to determine the involvement of these variants in the PDB pathophysiology. We also analysed the effect of a rare variant (RV −9906) found in OPTN promoter and described in our previous work [3].