| Abstract |
Pulmonary hypertension (PH) is a disease characterized by elevated pulmonary artery pressure, vasoconstriction, cell proliferation and vascular wall remodeling with resultant right ventricular hypertrophy and failure.
Lung inflammation has an important role in the initiation and maintenance of vascular remodeling and an increasing number of studies support the idea that this remodeling is a potential cause for the development of pulmonary hypertension. Pro-inflammatory cytokines and chemokines are involved in the pathogenesis of PH, such as CCL2 and CCL12. The levels of these cytokines are thought to be related to patients’ survival. PH is most commonly studied using the hypoxic animal model. Long-term exposure of mice to hypoxia leads to muscularization of small pulmonary arteries - increased expression of smooth muscle actin in cells - and recapitulates the elevation of right ventricular systolic pressure and the pathology of human disease.
Heme oxygenases (HO) are the rate-limiting enzymes that catalyze the conversion of heme into biliverdin, carbon monoxide (CO), and free iron. An increasing number of studies implicate HO-1 in the regulation of inflammation. Results from our lab indicate that lung-specific constitutive expression of HO-1 can suppress both the lung inflammation and the later development of pulmonary hypertension. Furthermore, overexpression in a lung-specific way of HO-1 was found to induce a switch in macrophage polarity toward an anti-inflammatory phenotype, and this effect was associated with protection from PH. Interestingly treatment of HO-1-/- mice with inhaled CO also protected them from pulmonary vascular remodeling.
MicroRNAs (miRNAs) are small noncoding transcripts of 16 to 29 nucleotide RNAs that regulate gene expression posttranscriptionally by targeting mRNAs. MicroRNAs have been shown to play important biological roles in various contexts; during development, cell differentiation, and immune regulation and also in pathologies such as cancer. To date more than 90 hypoxia-regulated miRNAs (HRMs) have been discovered.
In the present study, we utilized a bitransgenic mouse model, that was generated by crossing of mice that express the reverse tetracycline transactivator (rtTA) under the control of Clara cell secretory protein promoter (CC10) with mice
MiRNAs and Pulmonary Hypertension Konstantinou K. Georgios
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that harbor the human HO-1 transgene under the control of the bacterial tetracycline response element (TRE) and expressed HO-1 in a lung-specific, inducible way (tetOn system). By turning on and off HO-1 activity and modulating lung inflammatory response, our goal was to shed light on the nature of this hypoxia-induced inflammatory response and its role in the later development of the disease. Transgenic (SH01) mice for the HO-1 gene were also used.
Right ventricular systolic pressure, the Fulton Index, and the medial wall thickness index, were significantly elevated after 21 days of hypoxia in our bitransgenic mice. Doxycycline administration for the entire course of hypoxia prevented the increase in right ventricular systolic pressure, the Fulton Index, and the medial wall thickness index in a comparison with the water treaded control mice.
It has been shown in our study that hypoxia leads to induction of the fork-head box S1 (Foxs1) and the SRY box 17 (Sox17) transcription factors, which are found to be involved in the regulation of endothelial cell differentiation and vessel remodeling. Furthermore a striking increase of the Ankyrin repeat domain 37 (Ankrd37) a novel Hypoxia-inducible factor 1 (HIF-1) target gene was also observed. Hypoxia-induced mitogenic factor (HIMF/FIZZ1), a well-defined marker of alternative activated macrophages (M2) was altered by HO-1 expression both in the total lung and in the alveolar macrophages. Finally, the chemokine (C-C motif) ligand 2 (CCL2) and the chemokine (C-C motif) ligand 12 (CCL12) noncanonical inducers of M2 polarization were found to be suppressed by CO administration.
A potential role of miR-155 in the polarization of macrophages was demonstrated. Specifically CO induced the expression of miR-155 in total lung, which has been reported to target and decrease IL-13 receptor levels and subsequently the expression of the M2 phenotype. Moreover in order to identify the expression pattern of miRNAs induced by HO-1 during the first stages of pulmonary hypertension a miRNA array was performed.
Further understanding of the cellular and molecular pathways that contribute to the progression of pulmonary hypertension is needed, in order to lead to the development of targeted therapies, which may raise hope for the cure.
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The role of miRNAs in the pathogenesis of pulmonary arterial hypertension
