Identifying Potential Drug Targets for Sickle Cell Disease through Gene Expression and Pathway Analysis of GEO Data
Authors: Syed Sharjeel , Aljabban Jihad , Trujillo Jonathan , Syed Saad , Cameron Robert , Panahiazar Maryam , Hadley Dexter 
Published: November 2020

Background: The pathogenesis of sickle cell disease (SCD) and its complications have been well characterized down to the molecular level. However, there remains a relative dearth of disease modifying therapies that reduce the frequency and number of vas-occlusive crises, hospitalizations, and deaths. Recent advancements in utilizing hydroxyurea and L-glutamine, which both impact unique disease pathways, should pave way for the identification of other molecular pathways as ideal drug targets. In this regard, our meta-analysis serves to identify key genes and associated pathways that are differentially expressed in SC patients.
Methods: We employed our STARGEO platform to tag samples from the NCBI Gene Expression Omnibus and performed meta-analysis to compare SC and healthy control transcriptomes. For the meta-analysis, we tagged 285 peripheral blood samples from SC patients and 86 samples from healthy subjects as a control. We then analyzed the signature in Ingenuity Pathway Analysis to elucidate top disease functions from our analysis.
Results: From our meta-analysis, we identified iron homeostasis signaling, NRF2-mediated oxidative stress response, cell senescence, and pyrimidine interconversion/biosynthesis as top canonical pathways that were upregulated in the peripheral blood samples from SC patients. Top upstream regulators included membrane associated protein and transporter ABCB6, non-coding RNY3, and erythroid maturation transcription factors GATA1, KLF1, and HIPK2 (with predicted activation).
The most upregulated genes included inflammatory modulators RNF182 and IFI27, the latter of which has been shown to inhibit vascular endothelial growth and repair. Several membrane-associated protein coding genes such as GYPA, RAP1GAP, and PAQR9 were also upregulated in the SC samples. RAP1GAP is known to modulate neutrophil cell adhesion and homing while PAQR9 has roles in regulating protein quality control: a role also seen in similarly upregulated YOD1, a deubiquitinating enzyme involved in trafficking of misfolded proteins. Expectedly, also upregulated were HBBP1 and SOX6, which regulate globin genes and have been shown to silence γ-globin expression. Lastly, SLC6A19, the neutral amino acid transporter mutated in Hartnup disease, was also upregulated. Of the downregulated genes, WASF3, a member of the Wiskott-Aldrich syndrome protein family, has been linked to poor survival in many malignancies, including AML and CMML, but has not previously been linked to SCD pathogenesis. ENKUR was also downregulated and has been annotated as a tethering protein to cation channels as well as linked to pathways involving vascular leakage. SIGLEC10, which binds to vascular adhesion proteins, is a key suppressor of inflammatory responses to damage; it's downregulation along with ELAPOR1, a transmembrane protein involved in cellular response to stress, was also observed. Finally, based off the focus genes in our analysis we identified several networks with most being involved in amino acid metabolism, cellular assembly, function, and maintenance, hematological disease, and organismal injury. The top pathway is illustrated in Figure 1.
Conclusions: Our study illustrates differentially expressed gene activity in SCD consistent with known pathophysiology such as immune response, endothelial damage and adherence, heme metabolism, and globin regulation. We also showed evidence of genes not previously studied in SCD, which may have novel roles such as those part of the ubiquitin-proteasome system like YOD1 and RNF182. Additionally, while some genes in our analysis like EKLF and GAT1 have been shown to enhance δ-globin expression, paving way for possible drug therapies for B-hemoglobinopathies, others like IFI27, PAQR9, RAP1GAP, ENKUR, SIGLEC10, WASF3, and SOX9 have yet to be studied as mediators of disease pathogenesis in SCD. A target to SOX9, a known suppressor of γ-globin, or ABCB6, a known modulator of erythroid cell shape and hydration, have particularly promising potential as disease modifying therapies. Finally, HIPK2, HBBP1, and SLC6A19 have previously been shown to have intriguing effects on hydroxyurea dosing and responsivity in SC patients and may also be candidate target molecules to enhance existing therapies. These data identify potential candidate pathways for mechanistic studies seeking to confirm a causative role in the pathogenesis of sickle cell disease.

Disclosures
No relevant conflicts of interest to declare.