THE ROLE OF miRNA IN PRE-CAPILLARY PULMONARY HYPERTENSION: A COMPARISON BETWEEN GROUP 1 AND GROUP 3 PH

Rational: Lung transplantation is the final therapeutical approach to advanced parenchymal or vascular lung diseases. The current study recognize the substantial value of lung tissue obtained from explanted lungs for fundamental research purposes. By investigating small samples of paraffin-embedded explanted lungs affected by both group 3 and group 1 pulmonary hypertension, the study aim to uncover shared pathogenic mechanisms between these two groups through a comparative analysis of the quantitative expression patterns of a panel miRNAs among distinct groups. We considered miRNAs involved in pulmonary arterial endothelial disfunction and vascular remodelling: miR-140-5p, miR-24-1-5p, miR-103a-2-5p, miR-126-5p, miR-21-5p, miR-26a-5p, miR-20a-5p, miR-98-5p, miR-301a-5p, miR-17-5p, miR-92a-1-5p, miR-191-5p. Methods: Tissue samples were obtained from lung explants of patients who underwent lung transplantation and performed a right hearth catheterization during pre-transplant screening at IRCCS University Hospital of Bologna and at IRCCS San Matteo Hospital of Pavia from the 1st of January 2010 to the 31th of December 2021. 27 patients diagnosed with idiopathic pulmonary arterial hypertension (IPAH), idiopathic pulmonary fibrosis, or chronic obstructive pulmonary disease complicated by pulmonary hypertension (PH) were included. PH was defined as PAPm ≥ 25 mmHg, PVR > 3 WU and PCP < 15 mmHg on pre-transplant right heart catheterization. Key findings: analysis of continuous variables revealed a statistically significant difference in PAPm values between patients (IPAH vs IPF&COPD p<0.05), specifically higher values were found in comparison to group 3 pulmonary hypertension associated with IPF and COPD. Statically significant difference was also observed in the spirometric values of FEV1 and FVC, both in absolute values and as a percentage of predicted values (p<0.05). This difference reflects the in underlying diseases. Statistically significant difference was also observed in DLCO values as a percentage of predicted values between patients with IPAH compared to those in group 3, with higher mean values in group 1 (mean DLCO%: 64.11) than in patients with IPF (mean DLCO%: 26.18), and COPD (mean DLCO%: 17.80). Considering the analysed pathologies, the discrepancy in DLCO values may be attributed to different criteria used for listing patients for lung transplantation. In the miRNA expression analysis miR-21-5p resulted downregulated in IPAH vs IPF (unpaired t-test p<0.05), while miR-26a-5p resulted upregulated in IPAH vs IPF and COPD (unpaired t-test p<0.05). The expression level of the other miRNAs did not differ significantly between the 3 groups. Significance: Our study has demonstrated that miR-21 is down-regulated in patients with IPAH compared to patients with IPF and pulmonary hypertension. The role of miR-21 in relation to the findings of our study suggests that the higher expression of miR-21 in patients with group 3 PH may be justified by a greater hypoxic stimulus. Furthermore, the protective role on pulmonary vascular endothelium could account for the significantly lower values of PAPm observed in patients with group 3 PH compared to those with IPAH. Another result of our study highlights a statistically significant difference in the expression of miR-26, which is upregulated in patients with IPAH compared to patients with group 3 pulmonary hypertension, as well as those with IPF and COPD. The overexpression of miR-26 in patients with IPAH may be correlated with impaired differentiation of pulmonary arterial smooth muscle cells (PASMCs), thus contributing to inhibited PASMC differentiation and the development of pulmonary vascular pathology.