Single Nucleotide Polymorphisms in SAR1A Codon Regions Associated with Hydroxyurea Response in Sickle Cell Disease and Potentially Influenced in Mirnas Binding

Therapeutic induction of fetal hemoglobin (HbF) is one of the most promising approaches to ameliorate the severity of hemoglobinopathies such as β-thalassemia and sickle cell disease (SCD). Among HbF induction agents, hydroxyurea (HU) was approved by FDA to use for the treatment of SCD. However, there is variability in HU response among SCD patients. Individual genetic variants are mostly influenced in differences in pharmacological responsiveness to drug. We previously reported that the small guanosine triphosphate (GTP)-binding protein, secretion-associated and RAS-related (SAR1A) protein was a specific HU-inducible gene. The single nucleotide polymorphisms (SNPs) in SAR1A promoter also contributed to inter-individual differences in regulation of HbF expression and SCD patient responses to HU. Additionally, microRNAs (miRNAs) have been identified as potential key genes that regulate HbF induction and related with the clinical heterogeneity of SCD. Here, we demonstrate that SNPs within SAR1A coding regions are associated with differences in individual responses to HU therapy and potentially influenced in miRNAs binding.

In order to determine SNPs in SAR1A coding regions, we sequenced all 8 exons of SAR1A gene in 32 SCD patients. Three (rs56090714, rs3812693, rs56381518)and twenty-four (rs78341510, rs114346554, rs72807054, rs1370644731, rs1491135303, rs1412150420, rs1423653432, rs1480964347, rs1479076497, rs1180306451, rs1482823291, rs1275470720, rs201493587, rs1470556171, rs2394643, rs80028936, rs7919647, rs115340990, rs15801, rs1046747, rs79535872, rs7653, rs1280408553, and rs10586) variants were identified in codon 1 and 8, respectively. Interestingly, codon 2 was found a novel mutation at position 119, C>A. No mutation was detected in codon 3, 4, 5, 6 and 7. Among these SNPs, rs7919647 at codon 8 was highest frequency (96.9%) in SCD patients.

Next, we analyzed the association of SNPs and clinical and laboratory profiles using multiple regression. The rs56381518, rs1479076497, rs1180306451, rs1482823291, rs2394643 and rs115340990 showed significant association with total Hb levels after HU treatment in SCD patients. Only rs1180306451 was associated with absolute HbF levels (P= 0.0161). While no SNPs were observed significant association with HbF, F-cell or F-reticulocyte levels. In addition, the potential miRNAs binding to SNPs at 3'UTR regions were determined by using MicroSNiPer. We found miRNAs that may bind to SNPs as shown in Table 1. miR-625-5p, miR-5003-3p, miR-1236-5p, miR4271, miR-345-3p, miR4725-3p, miR-378a-3p, miR-548q and miR-135a-3p were previously identified only in mild-SCD patients. Furthermore, it has been reported that miR-1200 and miR-19b-1-5p were differentially expressed in high HbF levels condition. Our findings highlight the importance of genetic variants in SAR1A codon region that may predict the hydroxyurea response in SCD patients and miRNAs role in clinical heterogeneity of SCD.

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