Introduction

Non-traumatic intracerebral hemorrhage (ICH) is local bleeding into the parenchyma of the brain, which occurs because of rupture of cerebral blood vessels [1]. ICH usually develops when an atherosclerotic cerebral artery ruptures, the wall of which has undergone changes because of a prolonged existing increase in blood pressure [1]. The problem of early diagnosis, prognosis and treatment of ICH is one of the most important in modern medicine. Despite the vast experience of modern neurosurgery and neurology in the treatment of patients with ICH, the tactics of managing patients are still controversial, and indications for various methods of therapy need to be clarified [2]. Until now, neither conservative nor surgical methods of treatment have a clear advantage. Therefore, the study of the molecular mechanisms of the pathogenesis of ICH will deepen the understanding of the course of ICH and clarify some issues of diagnosis and treatment tactics. The mechanisms of ICH development include impaired blood-brain barrier (BBB) function and cerebral edema, cell apoptosis, inflammation, oxidative stress, activation of signaling pathways that regulate angiogenesis, endothelial disfunction, and suppression of signaling pathways responsible for maintaining the phenotype of vascular smooth muscle cells (VSMCs) [3]. MicroRNAs (miRNAs) are short, on average 18-22 nucleotides, single-stranded non-coding RNAs that post-transcriptional regulate gene expression by binding to the 3'-untranslated region (3'-UTR) of the messenger RNA (mRNA) target, which ultimately leads to decreasing protein expression by blocking translation and/or promoting degradation of the target mRNA [3] (Fig. 1). Many studies have shown that miRNAs play an important regulatory role in the occurrence and development of cerebrovascular diseases (CVDs). The mechanisms by which miRNAs play a role in the development of CVD are very complex (Table 1) [21]. Therefore, to understand the function of miRNAs and their role more clearly in diseases, including ICH, research on miRNA biology must be conducted in the context of a protein interaction network rather than isolated target genes. Moreover, proteins mediated by the same miRNA have a high propensity to interact with each other. These specific characteristics imply that miRNAs may exert their regulatory effects on protein complexes and pathways through a network of protein interactions [22]. Thus, based on the analysis of the network of protein interactions mediated by miRNAs, it is not possible to fully understand the function of miRNAs, but to more accurately identify miRNAs associated with ICH.

In addition, miRNA expression is controlled through DNA modification, such as methylation and transcription factors through the signal transduction pathway [23]. DNA methylation refers to the formation of a covalent bond between the 5' cytosine carbon of a DNA CpG dinucleotide (5'-cytosine-guanine-3') and a methyl group by DNA methyltransferase, forming 5-methylcytosine [23]. DNA hypermethylation can directly inhibit transcription or indirectly inhibit gene expression through transcriptional repression [24]. Changes in DNA methylation is associated with CVDs such as ischemic stroke (IS) and ICH [25, 26]. The hypermethylation of the CpG-rich promoter regions of vascular-specific miRNAs usually leads to their silencing through DNA methyltransferase (DNA MTase, DNMT) [27]. The abnormal DNA methylation of miRNA usually leads to the downregulation of miRNA, which is significantly related to the phenotypic switching of VSMCs or endothelial cells (ECs) disfunction [26]. In turn, miRNA could regulate the expression level of the target gene after transcription, which affects DNA methylation in ECs and VSMCs through the 3′-UTR of the RNA-induced silencing complex (RISC)-targeted DNMT mRNA [27]. In conclusion, this demonstrates the existence of a regulatory loop between miRNA expression and epigenetic modifications.

In recent years, the attention of researchers has been attracted by the study of changes in the expression levels of circulating miRNAs in various biological fluids of the human body for their potential consideration as non-invasive diagnostic and prognostic biomarkers of vascular dysfunction or damage brain tissue in CVDs (Table 2) [28,29,30,31,32,33,34,35,36]. Importantly, the specific expression signatures of circulating miRNAs in biological fluids reflect not only the existence of early-stage diseases, but also the dynamic development of late-stage diseases, disease prognosis, and treatment monitoring [19]. To date, a growing number of circulating miRNAs have been reported as potential noninvasive biomarkers in ICH, but the prospects for their practical application are still unclear. Thus, a summary of the circulating miRNA expression profile is of great importance for the identification of new promising biomarkers in ICH.

Table 2 Overview of circulating microRNAs (miRNAs) in patient’s biological fluids with cerebrovascular diseases. Note: studies examining non-traumatic intracerebral hemorrhage (ICH) were not included
Full size table

This review summarizes the brief data on miRNAs that have been proven to be involved in the pathogenesis of ICH, their targets, and mechanisms of action, and summarizes the latest advances in the context of the potential application of miRNAs in clinical practice, particularly, the possibility of their use in therapy and for early diagnosis, prognosis, and therapy monitoring for ICH. In addition, we will discuss important general questions about the possibilities of using as therapy drugs and biomarkers in ICH, uncovering the benefits of circulating miRNAs.

MiRNAs and the main pathogenetic elements of ICH

ICH is a multifactorial disease with many established causes. A key role in the pathogenesis of ICH is played by endothelial dysfunction and pronounced changes in the walls of cerebral vessels under the influence of chronically elevated blood pressure and atherosclerosis [1, 2]. The molecular basis for the development of ICH is complex and includes a whole range of disorders, among which the apoptosis of ECs of cerebral vessels and neurons, the inflammatory process and the response of the immune system, oxidative stress, impaired BBB function, and cerebral edema occupy a central place [1, 2]. It is widely known that miRNAs are powerful regulators involved in all molecular and cellular processes, both in normal conditions and in various diseases [21, 22]. Understanding the regulation of miRNAs and their targets makes it possible to determine the causes of the occurrence of ICH caused by changes in gene expression. Several in vitro and in vivo studies have provided clear evidence of the involvement of miRNAs in the pathogenesis of the development and progression of ICH, which will be described in this chapter (Table 3) [37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73].

Table 3 MicroRNAs (miRNAs) and their target genes involved in the main elements of pathogenesis non-traumatic intracerebral hemorrhage (ICH). Note: in vitro and in vivo studies, expression level shown during application anti-miRNA or miRNA mimics
Full size table

Vascular integrity and extracellular matrix remodeling

Maintaining vascular integrity and preserving the extracellular matrix (ECM) are crucial for preventing ICH. Disruptions in the BBB and abnormalities in the ECM contribute to increased vascular permeability and vessel fragility, leading to hemorrhage. The BBB, consisting of ECs, tight junctions, pericytes, and astrocytes, regulates the passage of molecules and cells between the bloodstream and the brain parenchyma [74]. Dysfunction of the BBB is associated with increased permeability, allowing blood components to enter the brain parenchyma, and triggering neuroinflammatory responses. Participation of miRNAs in the regulation of the BBB function occurs largely due to the influence on the cytoskeleton of ECs and on the functional state of cell adhesion proteins [75, 76].

The main cause of ICH is hypertension and associated microangiopathy. Prolonged arterial hypertension contributes to the formation of lipogyalinosis, and subsequently fibrinoid necrosis of the walls of perforating arteries, characterized by the absence of anastomoses with other vessels. Under these conditions, the structure and organization of cell adhesion proteins in the outer membrane of the ECs leads to disruption of BBB permeability (reduced levels of cell adhesion proteins such as claudin 5, occludin and zonula occludens-1 (ZO-1) have been shown) [74, 75]. ZO-1 is an important tight junction protein involved in the formation of the BBB. It is involved in the barrier function, in the regulation of cell transport, cell polarity, cell proliferation and differentiation [77]. An increase or decrease in ZO-1 expression in ECs of the brain microvascular network also significantly affects apoptosis and proliferation of ECs [78]. Hu et al. found that ZO-1 is a potential target for miR-23a-3p. Their data showed that proliferation and apoptosis of hCMEC/D3 cells are regulated by via miR-23a-3p/ZO-1 axis, demonstrating also that aberrant expression of miR -23a-3p promotes the formation of perihematomal edema [59]. In addition, the degradation of cell adhesion proteins by matrix metalloproteinases (MMPs) is also directly regulated by miRNAs [79]. Some miRNAs can protect the integrity of the BBB by reducing immune cell adhesion and the expression of pro-inflammatory cytokines. Activation of microglia in the process of BBB permeability impairment, in turn, exacerbates ICH-induced damage to brain tissue and, thereby, significantly worsens the prognosis and neurological deficit [80, 163]. This requires the identification of a more specific biomarker associated with damage to the vascular elements of the cerebral arteries, in addition, these biomarkers do not reflect cellular function. There is already ample evidence that miRNAs play an important role in the processes underlying the normal function of ECs and VSMCs and their dysfunction [164,165,166,167,168,169]. And the fact that some miRNAs are found freely circulating in biological fluids indicates an early manifestation of damage to the vascular wall of cerebral arteries. Due to their specificity and ability to be detected in the early stages of disease development, circulating miRNAs can undoubtedly be considered as predictors of the onset of ICH (Fig. 6).

Fig. 6
figure 6

Schematic illustration of the regulatory role of microRNAs (miRNAs) in vascular wall cells (endothelial cells (ECs) and vascular smooth muscle cells (VSMCs)) and their secretion into the bloodstream. Vascularly enriched miRNAs regulate cellular responses to various factors both in normal and pathological conditions by acting on various receptors and signaling pathways: miR-15a - decreases blood-brain barrier (BBB) disruption and protection of cerebral ECs apoptosis; miR-17-92, miR-210 and miR-132 - angiogenesis; miR-23a - inhibition of ECs growth; miR-26a - increase VSMCs proliferation and control VSMC phenotype shifting; miR -143/145 and miR-146a - activation of VSMCs proliferation and neointimal hyperplasia; miR-24 - inhibition of erythropoiesis and control VSMC phenotype shifting; miR-221/miR-222 - pro-proliferative effect on ECs and angiogenesis. In addition, it is known from recent sources that these vascular-enriched miRNAs can occur in the bloodstream and may be biomarkers of early damage to the vascular wall. Note: Bax, Bcl-2-associated X protein; Bcl-2, B-cell lymphoma 2; CTGF, connective tissue growth factor; EGF, epidermal growth factor; Elk-1, ETS domain-containing protein 1; ERK, extracellular signal-regulated kinase; FGF, fibroblast growth factor; GAX, homeobox protein; KLF4, krüppel-like factor 4; KLF5; krüppel-like factor 5; MEK, mitogen-activated protein kinase kinase; PI3K, Phosphatidyl-inositol 3-kinase; p120RasGAP, p21, cyclin-dependent kinase inhibitor 1; Rb, Retinoblastoma; p, Hpophosphorylated; Raf, rapidly growing fibrosarcoma; Ras, rat sarcoma; RhoA, Ras homolog gene family member A; Smurf1, Smad ubiquitin-regulatory factor 1; SRF, serum response factor; TGF-b, transforming growth factor beta; Trb-3, Tribbles-like protein-3; TSR1, thrombospondin-1; VEGF, vascular endothelial growth factor; ZEB2, zinc finger Ebox- binding homeobox 2.

Full size image

Circulating miRNAs as biomarkers of neuroinflammation

As discussed above, neuroinflammation after ICH is a complex process of interaction between the immune and nervous systems, which occurs in response to damage to the nervous tissue from the hematoma mass effect and can continue for a long period after the hemorrhage [86]. In addition, the lysis of erythrocytes and the reaction of the brain tissue to decay products leads to the death of neurons, in response to which the process of neuroinflammation is triggered as a neuroprotective mechanism that provides protection for intact tissue: microglia are activated, infiltration by granulocytes and lymphocytes of the brain tissue, secretion by immunocompetent and glial pro- and anti-inflammatory cytokines, chemokines, and ROS cells [86, 99]. Adverse consequences and complications of ICH are associated with secondary damage and the development of neuroinflammation. Therefore, recognizing and determining the extent of the inflammatory process at an early stage is essential for optimizing immune-targeted treatment. On the other hand, diagnostic difficulties are due to nonspecific changes according to neuroimaging data. It has been repeatedly shown that miRNAs play a direct role as pro- or anti-inflammatory regulators after ICH, their presence in biological fluids presents the possibility of their use as prognostic biomarkers for the development of neuroinflammation. Hematoma growth and a large hematoma volume are associated with an unfavorable course of the disease, including the activation of inflammatory cascades. To date, there are already successful results from several studies that have shown that circulating miRNAs can be used to predict hematoma growth after ICH [59, 147]. In addition, besides EVs or protein complexes, miRNAs are expressed in erythrocytes, and due to their lysis, circulating miRNAs in apoptotic bodies can enter the bloodstream or CSF (when blood enters the lateral ventricles) and can potentially provide easy and rapid testing in clinical populations, hel** to predict and monitor the degree of development of neuroinflammation [172, 173]. It is important to note that not every laboratory indicator can be called a biomarker. The main thing that distinguishes a biomarker is its statistically substantiated relationship with the disease, complication, and treatment effect, which is expressed in the following characteristics: statistical significance of differences in the selected characteristic, receiver operating characteristic curve (ROC), Kaplan–Meier curves, threshold value with calculated sensitivity and specificity, predictive value of the biomarker, likelihood ratio for the presence and absence of the trait and accuracy index [172, 173]. In most studies, circulating miRNAs are named as potential biomarkers based on their statistically significant increase or decrease in expression in ICH [188, 189]. Dysregulation of miR-124 is associated with the development of CVDs such as ICH. Recently, abnormal expression of miR-124 was shown to be associated with the occurrence and development of ICH via regulating microglia function [58, 69, 195]. Moreover, miR-126 is involved in vascular inflammation and neuroinflammation [195, 196]. Amongst miRNAs, miR-126 is one of the most highly-expressed and highly-studied in ICH [37,38,39,5, circulating miRNAs are associated with a higher incidence of complications or adverse outcomes of ICH. Such an association is not enough to classify circulating as diagnostic or prognostic biomarkers; an in-depth statistical analysis is required, which will allow to identify multifactorial relationships, evaluate the significance, and calculate the diagnostic or prognostic characteristics of the test with the obligatory use of ROC analysis. It is also necessary to increase the number of studies on the use of circulating miRNAs in the differential diagnosis of stroke subtypes (ICH vs SAH or IS). Nevertheless, further study of circulating miRNAs makes it possible to predict the level of damage to the cerebral vessel wall and the likelihood of its rupture, as well as to confirm the fact of an event that occurred in real time and determine the period of ICH (acute, subacute and chronic), distinguish its subtypes and even judge the prognosis.