MiRNAs have been considered as potential biomarkers in several cardiovascular and metabolic diseases, including H, T2DM and OB. However, few studies have associated the deregulation of these miRNAs with clinical and laboratory parameters in these diseases. Thus, the present study evaluated the expression of circulating miRNAs (miR-1-3p, miR-21-5p and miR-126-5p) in the serum of patients with H, T2DM and OB and performed correlation analysis with clinical and laboratory parameters.
Our results revealed for the first time that the circulating miR-126-5p is significantly increased in serum from the H group compared to the CTL group and showed positive correlation of miR-126-5p with creatinine and a negative correlation with platelets, however there was no difference statistic in the expression of miR-126-5p of group H compared with group HDO, including there was also no statistical difference in the HDO group compared to the CTL.
In this context, an elegant study corroborates our results regarding the overexpression of miR-126 circulating in the whole blood in hypertensive patients compared to the control group [45], however the authors did not find correlations with creatinine and platelets. Another study by the same research group mentioned above, again showed the high expression of miR-126-3p circulating in the whole blood of South African hypertensive patients with chronic kidney disease due to H, they also identified a positive correlation with creatinine [38] but not with platelets.
MiR-126 is associated with the process of angiogenesis and regulates vascular integrity [46], being abundantly expressed in endothelial cells [47]. MiR-126 was also overexpressed in glomerular endothelial cells in response to tumor necrosis factor-α (TNF-α), demonstrating that a disease with an increased inflammatory profile favors elevated expression of this miRNA in glomerular endothelial cells, inducing glomerular and renal dysfunction [48].
Furthermore, it is well described in the literature that long-term high blood pressure levels are associated with injury and structural and functional changes in renal arteries and arterioles, causing loss of glomerular and tubulointerstitial function of the kidneys and in some cases promoting a reduction in glomerular filtration rate, characterizing the chronic kidney disease [50]. With the loss of kidney function and reduced glomerular filtration rate, accumulation of some toxins such as urea, potassium and creatinine usually occurs [51].
In our study, we identified a positive correlation of the increase in miR-126-5p with creatinine, but we did not identify a correlation with glomerular filtration rate. Thus, we can suppose that overexpressed miR-126-5p in the serum of hypertensive patients may be a potential biomarker of the onset of loss of renal function or acute kidney injury, that is associated with an increase in creatinine [51].
In this context, a study corroborates this assumption, because the authors demonstrated the elevation of miR-126-3p expression in the whole blood of patients with chronic kidney disease, also demonstrating a positive correlation with creatinine, including they showed a correlation with the rate of glomerular filtration [38], demonstrating that this other strand (3p) of miR-126 can be a biomarker of the most advanced chronic stage of kidney disease. This variation in the function of the two strands of the same miRNA may be due to their different nucleotide structures in the mature state [52]. Furthermore, studies support our theory demonstrating that increased miR-126 is involved with loss of function and vascular damage of the kidneys [36, 37].
In our work, in addition to miR-126-5p, we also identified a positive correlation of miR-21-5p with creatinine, but we also did not identify a correlation of this miRNA with glomerular filtration rate. MiR-21 has already been shown to be overexpressed in peripheral blood mononuclear cells from hypertensive patients, modulating the phenotype of vascular smooth muscle cells, inducing arterial remodeling and correlation with blood pressure [34].
MiR-21 also plays a role in the increased inflammatory profile [53] and activates TGF-β, promoting renal fibrosis [54]. Both pathophysiological processes can induce renal arteriole dysfunction, loss of kidney function with a consequent increase in creatinine, which may explain the positive correlation of miR-21 with creatinine, as observed in our study, although we have not identified a statistical difference in miR-21 expression in the H group compared to the CTL group or the HDO group. The other miRNA that we evaluated, miR-1-3p, did not show a significant difference in its expression when comparing the groups and we also did not identify a correlation with creatinine or with platelets.
We also identified a negative correlation of miR-126-5p expression with platelets. It is described in the literature that in the hypertensive pathophysiological process there is a prothrombotic or hypercoagulant state with an increase in the amount and activation of platelets [55] and this favors the atherosclerotic process in these patients [56]. Thus, the negative correlation of miR-126-5p with platelets may be due to the antihypertensive drugs that these patients were using, given that some drugs decrease platelet activation [57], attenuate platelet aggregation [58] and induce thrombocytopenia [59–61], however, the molecular mechanisms that are associated with the high expression of miR-126-5p may be reducing the number of platelets in hypertensive patients with the use of antihypertensive drugs still need to be elucidated.
Finally, we performed an analysis in DIANA TOOLS to observe the biological processes regulated by these three miRNAs to complement the understanding of the function of these miRNAs. We identified that both miRNA-21-5p and miRNA-126-5p regulate platelet activation and degranulation, which may explain the negative correlation we found of miR-126-5 with platelets. It was also observed that these two miRNAs respond to stress, in addition to inducing modification of gene expression by regulating fibroblast growth factor receptor signaling, which can promote an increase in the fibrotic process, including regulating the cell death and catabolic process, which can clarify how damage to glomerular endothelial cells occurs, leading to kidney damage.
Limitations
We had some limitations of our study. This study was carried out in the period of the COVID-19 pandemic and not all patients were going to HUPES, so the sample number was relatively small. Another limitation was that the participants were not matched by age, however the age factor did not influence the increase in miR-126-5p expression in the H group, because the HDO group had the highest mean age and in this group we did not observe a high expression of miR-126-5p, moreover there was no correlation of age with miR-126-5p as shown in the correlation analysis.
Future Directions
More studies are needed to demonstrate the importance of overexpression of this miRNA in hypertensive individuals and the correlation of this molecule with clinical and laboratory parameters. Furthermore, therapies or drugs can be implemented to inhibit this miRNA to observe blood pressure levels as well as analyze kidney function.