Olga Rafikova

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Scholarly Contributions

Journals/Publications

• Rafikov, R., & Rafikova, O. (2017). Pulmonary arterial hypertension: are we close to the success?. Journal of Clinical Respiratory Medicine, 1(1), 1-3.
• Sakipov, S., Rafikova, O., Kurnikova, M. G., & Rafikov, R. (2017). Molecular mechanisms of bio-catalysis of heme extraction from hemoglobin. Redox biology, 11, 516-523.
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  Red blood cell hemolysis in sickle cell disease (SCD) releases free hemoglobin. Extracellular hemoglobin and its degradation products, free heme and iron, are highly toxic due to oxidative stress induction and decrease in nitric oxide availability. We propose an approach that helps to eliminate extracellular hemoglobin toxicity in SCD by employing a bacterial protein system that evolved to extract heme from extracellular hemoglobin. NEAr heme Transporter (NEAT) domains from iron-regulated surface determinant proteins from Staphylococcus aureus specifically bind free heme as well as facilitate its extraction from hemoglobin. We demonstrate that a purified NEAT domain fused with human haptoglobin β-chain is able to remove heme from hemoglobin and reduce heme content and peroxidase activity of hemoglobin. We further use molecular dynamics (MD) simulations to resolve molecular pathway of heme transfer from hemoglobin to NEAT, and to elucidate molecular mechanism of such heme transferring process. Our study is the first of its kind, in which simulations are employed to characterize the process of heme leaving hemoglobin and subsequent rebinding with a NEAT domain. Our MD results highlight important amino acid residues that facilitate heme transfer and will guide further studies for the selection of best NEAT candidate to attenuate free hemoglobin toxicity.
• Chen, F., Wang, Y., Rafikov, R., Haigh, S., Zhi, W. B., Kumar, S., Doulias, P. T., Rafikova, O., Pillich, H., Chakraborty, T., Lucas, R., Verin, A. D., Catravas, J. D., She, J. X., Black, S. M., & Fulton, D. J. (2016). RhoA S-nitrosylation as a regulatory mechanism influencing endothelial barrier function in response to G(+)-bacterial toxins. Biochemical pharmacology.
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  Disruption of the endothelial barrier in response to Gram positive (G(+)) bacterial toxins is a major complication of acute lung injury (ALI) and can be further aggravated by antibiotics which stimulate toxin release. The integrity of the pulmonary endothelial barrier is mediated by the balance of disruptive forces such as the small GTPase RhoA, and protective forces including endothelium-derived nitric oxide (NO). How NO protects against the barrier dysfunction is incompletely understood and our goal was to determine whether NO and S-nitrosylation can modulate RhoA activity and whether this mechanism is important for G(+) toxin-induced microvascular permeability. We found that the G(+) toxin listeriolysin-O (LLO) increased RhoA activity and that NO and S-NO donors inhibit RhoA activity. RhoA was robustly S-nitrosylated as determined by biotin-switch and mercury column analysis. MS revealed that three primary cysteine residues are S-nitrosylated including cys16, cys20 and cys159. Mutation of these residues to serine diminished S-nitrosylation to endogenous NO and mutant RhoA was less sensitive to inhibition by S-NO. G(+)-toxins stimulated the denitrosylation of RhoA which was not mediated by S-nitrosoglutathione reductase (GSNOR), thioredoxin (TRX) or thiol-dependent enzyme activity but was instead stimulated directly by elevated calcium levels. Calcium-promoted the direct denitrosylation of WT but not mutant RhoA and mutant RhoA adenovirus was more effective than WT in disrupting the barrier integrity of human lung microvascular endothelial cells. In conclusion, we reveal a novel mechanism by which NO and S-nitrosylation reduces RhoA activity which may be of significance in the management of pulmonary endothelial permeability induced by G(+)-toxins.
• Rafikova, O., Meadows, M. L., Kinchen, J. M., Mohney, R. P., Maltepe, E., Desai, A. A., Yuan, J. X., Garcia, J. G., Fineman, J. R., Rafikov, R., & Black, S. M. (2016). Metabolic Changes Precede the Development of Pulmonary Hypertension in the Monocrotaline Exposed Rat Lung. PloS one, 11(3), e0150480.
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  There is increasing interest in the potential for metabolic profiling to evaluate the progression of pulmonary hypertension (PH). However, a detailed analysis of the metabolic changes in lungs at the early stage of PH, characterized by increased pulmonary artery pressure but prior to the development of right ventricle hypertrophy and failure, is lacking in a preclinical animal model of PH. Thus, we undertook a study using rats 14 days after exposure to monocrotaline (MCT), to determine whether we could identify early stage metabolic changes prior to the manifestation of developed PH. We observed changes in multiple pathways associated with the development of PH, including activated glycolysis, increased markers of proliferation, disruptions in carnitine homeostasis, increased inflammatory and fibrosis biomarkers, and a reduction in glutathione biosynthesis. Further, our global metabolic profile data compare favorably with prior work carried out in humans with PH. We conclude that despite the MCT-model not recapitulating all the structural changes associated with humans with advanced PH, including endothelial cell proliferation and the formation of plexiform lesions, it is very similar at a metabolic level. Thus, we suggest that despite its limitations it can still serve as a useful preclinical model for the study of PH.
• Rafikova, O., Rafikov, R., Kangath, A., Qu, N., Aggarwal, S., Sharma, S., Desai, J., Fields, T., Ludewig, B., Yuan, J. X., Jonigk, D., & Black, S. M. (2016). Redox regulation of epidermal growth factor receptor signaling during the development of pulmonary hypertension. Free radical biology & medicine, 95, 96-111.
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  The development of pulmonary hypertension (PH) involves the uncontrolled proliferation of pulmonary smooth muscle cells via increased growth factor receptor signaling. However, the role of epidermal growth factor receptor (EGFR) signaling is controversial, as humans with advanced PH exhibit no changes in EGFR protein levels and purpose of the present study was to determine whether there are post-translational mechanisms that enhance EGFR signaling in PH. The EGFR inhibitor, gefinitib, significantly attenuated EGFR signaling and prevented the development of PH in monocrotaline (MCT)-exposed rats, confirming the contribution of EGFR activation in MCT induced PH. There was an early MCT-mediated increase in hydrogen peroxide, which correlated with the binding of the active metabolite of MCT, monocrotaline pyrrole, to catalase Cys377, disrupting its multimeric structure. This early oxidative stress was responsible for the oxidation of EGFR and the formation of sodium dodecyl sulfate (SDS) stable EGFR dimers through dityrosine cross-linking. These cross-linked dimers exhibited increased EGFR autophosphorylation and signaling. The activation of EGFR signaling did not correlate with pp60(src) dependent Y845 phosphorylation or EGFR ligand expression. Importantly, the analysis of patients with advanced PH revealed the same enhancement of EGFR autophosphorylation and covalent dimer formation in pulmonary arteries, while total EGFR protein levels were unchanged. As in the MCT exposed rat model, the activation of EGFR in human samples was independent of pp60(src) phosphorylation site and ligand expression. This study provides a novel molecular mechanism of oxidative stress stimulated covalent EGFR dimerization via tyrosine dimerization that contributes into development of PH.
• Rafikov, R., Sun, X., Rafikova, O., Meadows, M. L., Desai, A. A., Khalpey, Z., Yuan, J. X., Fineman, J. R., & Black, S. M. (2015). Complex I dysfunction underlies the glycolytic switch in pulmonary hypertensive smooth muscle cells. Redox biology, 6, 278-86.
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  ATP is essential for cellular function and is usually produced through oxidative phosphorylation. However, mitochondrial dysfunction is now being recognized as an important contributing factor in the development cardiovascular diseases, such as pulmonary hypertension (PH). In PH there is a metabolic change from oxidative phosphorylation to mainly glycolysis for energy production. However, the mechanisms underlying this glycolytic switch are only poorly understood. In particular the role of the respiratory Complexes in the mitochondrial dysfunction associated with PH is unresolved and was the focus of our investigations. We report that smooth muscle cells isolated from the pulmonary vessels of rats with PH (PH-PASMC), induced by a single injection of monocrotaline, have attenuated mitochondrial function and enhanced glycolysis. Further, utilizing a novel live cell assay, we were able to demonstrate that the mitochondrial dysfunction in PH-PASMC correlates with deficiencies in the activities of Complexes I-III. Further, we observed that there was an increase in mitochondrial reactive oxygen species generation and mitochondrial membrane potential in the PASMC isolated from rats with PH. We further found that the defect in Complex I activity was due to a loss of Complex I assembly, although the assembly of Complexes II and III were both maintained. Thus, we conclude that loss of Complex I assembly may be involved in the switch of energy metabolism in smooth muscle cells to glycolysis and that maintaining Complex I activity may be a potential therapeutic target for the treatment of PH.
• Rafikova, O., Rafikov, R., Meadows, M. L., Kangath, A., Jonigk, D., & Black, S. M. (2015). The sexual dimorphism associated with pulmonary hypertension corresponds to a fibrotic phenotype. Pulmonary circulation, 5(1), 184-97.
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  Although female predominance in the development of all types of pulmonary hypertension (PH) is well established, many clinical studies have confirmed that females have better prognosis and higher survival rate than males. There is no clear explanation of why sex influences the pathogenesis and progression of PH. Using a rat angioproliferative model of PH, which closely resembles the primary pathological changes observed in humans, we evaluated the role of sex in the development and progression of PH. Female rats had a more pronounced increase in medial thickness in the small pulmonary arteries. However, the infiltration of small pulmonary arteries by inflammatory cells was found only in male rats, and this corresponded to increased myeloperoxidase activity and abundant adventitial and medial fibrosis that were not present in female rats. Although the level of right ventricle (RV) peak systolic pressure was similar in both groups, the survival rate in male rats was significantly lower. Moreover, male rats presented with a more pronounced increase in RV thickness that correlated with diffuse RV fibrosis and significantly impaired right cardiac function. The reduction in fibrosis in female rats correlated with increased expression of caveolin-1 and reduced endothelial nitric oxide synthase-derived superoxide. We conclude that, in the pathogenesis of PH, female sex is associated with greater remodeling of the pulmonary arteries but greater survival. Conversely, in males, the development of pulmonary and cardiac fibrosis leads to early and severe RV failure, and this may be an important reason for the lower survival rate among males.

Presentations

• Rafikova, O. (2015, November). Reductive stress associated with male gender contributes to the pulmonary hypertension and right ventricle dysfunction.. SFRBM meeting, Boston MA.

Poster Presentations

• McBride, M. L., Williams, E. R., Langlais, P. R., Mandarino, L. J., Rafikov, R., & Rafikova, O. (2017, June). Inositol Monophosphate 1 (IMPA1) And Rage Interaction: The Role Of Novel Proliferative Pathway In Pulmonary Hypertension. American Heart Association.
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  This is a very first evidence that damage induced RAGE activation is involved in protection from glycolysis-mediated osmotic stress and activation of Akt pathway in PAH by the formation of RAGE/IMPA1 complex.
• Rafikov, R., Srivastava, A., Desai, A., Langlais, P. R., Zemskov, E., Mandarino, L. J., & Rafikova, O. (2017, June). Hemolysis-mediated vascular permeability in lungs contributes to the development of pulmonary hypertension. American Heart Association.
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  Our data indicate that PH patients have increased levels of free Hb in plasma that correlate with disease severity and progression. There is also a significant accumulation of free Hb and depletion of haptoglobin in the sugen/hypoxia rat model. In rats, perivascular edema was observed during first two weeks of PH concomitant with increased infiltration of inflammatory cells. In the cell culture model of HLMVECs, we found that not hemoglobin but free heme-induced endothelial permeability via activation of the p38/HSP27 signaling pathway. Indeed, the rat model also exhibited an increased activation of p38/HSP27 during the initial phase of PH. Surprisingly, despite the increased levels of hemolysis and heme-mediated signaling; there was no heme oxygenase-1 activation. This can be explained by observed destabilization of HIF1a during the first two weeks of PAH regardless of hypoxic conditions. We found that heme-mediated effects on endothelium, at least in part, depend on Heme Carrier Protein 1 (HCP-1) and pharmacological inhibition of HCP-1 by sulfasalazine reduced barrier disruptive potential of the heme. Sulfasalazine administration to sugen/hypoxia rats results in attenuation of PH by a reduction in vascular remodeling in the lungs as well as decreasing right heart hypertrophy.
• Rafikova, O. (2015, July). Akt Mediated Mitochondrial Dysfunction Involves Mitochondrial Endothelial Nitric Oxide Synthase Translocation. AHA BCVS meeting, New Orleans, LA..
• Rafikova, O. (2015, July). Pulmonary Hypertension Induced Right Ventricle Fibrosis is Associated with Male Gender. AHA BCVS meeting, New Orleans, LA.
• Rafikova, O. (2015, November). Complex I dysfunction dictates glycolytic switch in pulmonary hypertensive smooth muscle cells.. SFRBM meeting, Boston MA.
• Rafikova, O. (2015, November). Metabolic changes precede the development of pulmonary hypertension in monocrotaline model.. SFRBM meeting, Boston MA.
• Rafikova, O. (2015, November). Targeted protein protection from oxidative/nitrosative post-translational modifications using shielding peptides.. SFRBM meeting, Boston MA.