Compared with TCs in the intestine and skin, cTCs, due to being in the heart tissue that is under continuous mechanical stress and needing to withstand greater tension and provide effective mechanical support during myocardial contraction and relaxation, usually have relatively thicker Tps that are relatively shorter in length. Moreover, to ensure the efficient transmission of mechanical signals and the maintenance of cellular stability in the complex mechanical environment of the heart, the beaded structure of their Tps may be more compact. The cell bodies of cTCs are relatively smaller and more regular, usually oval or spindle-shaped. This shape helps the cells to be closely arranged between the myocardial fibers, so as to better perform their functions of mechanical support and signal transduction (30–32).

However, in intestinal tissue, the cell bodies of TCs tend to be relatively elongated and exhibit a slight spindle shape, which is an adaptive feature to accommodate the intestinal peristalsis and the complex tissue architecture (33, 34). In lung tissue, TCs often display a more flattened morphology, enabling them to attach more effectively to the alveolar surface or establish tight junctions with adjacent cells (35). In neural tissue, the Tps of TCs are typically shorter and sparsely distributed, primarily forming local networks around the neuronal cell bodies or axons (36). Within the liver, the protrusions of TCs are usually longer and more extensively distributed, traversing the hepatic lobules and playing a significant role in the metabolic and immune regulatory functions of the liver (37, 38). In skin tissue, the branches of TCs protrusions are relatively fewer in number and more regular in pattern, presenting an orderly arrangement that helps maintain the skin's elasticity and barrier function (39). In pancreatic tissue, the branches of TCs protrusions are relatively complex and may engage in close interactions with islet cells and ductal cells, thereby participating in the regulation of the pancreas's endocrine and exocrine functions (40). In immune tissue, TCs can interact with immune cells via immunological synapses, actively participating in the transmission of immune signals and the regulation of immune responses (41). Meanwhile, in reproductive tissue, TCs may form specific connections with germ cells, providing essential support and protection for the development and maturation of these cells (42).

The myocardium is composed of a diverse assortment of interstitial cells, each of which plays a crucial role in both the physiological and pathological facets of cardiac function (43). Take fibroblasts, they provide vital mechanical support and contribute to the structural organization of cardiomyocytes, thus maintaining the heart's normal morphology and functionality (44). cTCs, distinguished by their elaborate network of protrusions, play a significant role in facilitating intercellular signaling, thereby helping to maintain cardiac electrical stability (14). Mesenchymal stem cells, with their remarkable plasticity, can differentiate into cardiomyocytes and endothelial cells following myocardial injury, thereby facilitating the repair and regeneration processes (45). Lymphocytes are essential for modulating the cardiac immune response, as they help to suppress excessive inflammation and protect against further tissue damage (46). Endothelial cells, through the secretion of growth factors, promote angiogenesis, increasing myocardial blood flow and facilitating functional recovery (47). Nevertheless, these interstitial cells display considerable heterogeneity in terms of their abundance, spatial distribution, immune profiles, and primary functions, as elaborated in Table 1.

The distinctive physical and structural characteristics of cTCs, in contrast to other cells, are their relatively small cell bodies (ranging from 9 to 15 μm) and the multiple slender Tps that extend from the cell body, with lengths reaching up to 100 μm. Among these features, the most significant structural attribute that sets cTCs apart from other cell types is the presence of these unique Tps. Depending on the number of Tps, the cell body of cTCs can exhibit different shapes, such as pear-shaped, fusiform-shaped, triangle-shaped, star-shaped (48). The nucleus makes up approximately 25% of the cell volume and contains clusters of heterochromatin attached to the nuclear membrane (16, 49). The cytoplasm contains many subcellular structures including mitochondria, golgi apparatus, endoplasmic reticulum, and cytoskeleton (50–52). Each Tps has a length of approximately tens to hundreds of micrometers and a width of around 0.10 ± 0.05 micrometers. Due to the extremely narrow width of Tps, it is challenging to observe under ordinary optical microscopes their extension into the surrounding matrix and the formation of connections with other cells. When Tps are observed under an electron microscope, their rosary-like structure becomes apparent. This structure is characterized by alternating regions of expansion and constriction. Additionally, Ca²⁺-release units andorganelles such as endoplasmic reticulum, mitochondria, and vesicles were observed at the level of the dilations (53), that were beneficial for the function of mitochondria and endoplasmic reticulum, and also plays a positive role in the transport of exosomes and vesicles (10), as shown in Figure 1.

cTCs exhibit certain differences in molecular markers compared with TCs in other tissues. These differences reflect their specific functions and adaptabilities in different tissue microenvironments. Cluster of differentiation 34(CD34), c-Kit, and platelet-derived growth factor receptor α/β (PDGFR-α/β) are common surface markers of cTCs (54, 55). In the heart, the expression of CD34 helps cTCs interact with other cells (such as cardiomyocytes and vascular endothelial cells), participating in the repair and regeneration of cardiac tissue. c-Kit may be involved in regulating the growth and differentiation of cardiomyocytes, as well as the regeneration and repair processes of cardiac tissue. The PDGFR-α/β signaling pathway plays an important role in cardiac development, myocardial hypertrophy, and the occurrence and development of cardiac diseases. α-Actin and connexin 43 (Cx43) are markers within the cytoplasm of cTCs. α-Actin may be involved in regulating the mechanical contraction function of cells, while Cx43 is involved in intercellular electrical signal transduction, which is crucial for maintaining normal heart rhythm and electrophysiological activities in the heart (56). VEGF and HGF are important secretory molecular markers of cTCs (22). VEGF can promote angiogenesis and increase vascular permeability, which is of great significance for maintaining the blood supply of the myocardium and the normal function of the heart. HGF has various biological functions, such as promoting cell proliferation, migration, and differentiation, and may be involved in regulating the growth and repair of cardiomyocytes, as well as the reconstruction of the myocardial interstitium. In intestinal TCs, the expression of vimentin is relatively significant. Integrin β4 is an important surface marker of skin TCs (57). Neurofilaments are one of the important intracellular markers of TCs in nerve tissue (58). Cytokeratins are the main structural proteins of hepatic TCs. In pulmonary TCs, more surfactant-related proteins may be secreted, while renal TCs may secrete molecules related to renal physiological functions, such as renin (59).

Enzymatic digestion stands as the predominant technique employed for isolating cTCs (60). Initially, an appropriate sample of heart tissue is procured and subsequently minced into smaller portions. These tissue pieces are then transferred into a digestion medium comprising 1–3 mg/ml of type I collagenase, where the digestion process unfolds at 37℃ over a duration of 30–60 min. Following this, the digested tissue suspension is filtered using a mesh (commonly ranging between 100–200 μm) to yield a single-cell suspension enriched with heart cells. Various methodologies are employed for the purification of cTCs, notable among which are density gradient centrifugation, immunomagnetic bead separation, and flow cytometric sorting. Immunological markers such as c-Kit, CD34⁺, and PDGFR-α are frequently utilized in identifying cTCs. Leveraging these specific immune markers, the purification process culminates in the acquisition of cTCs with a high degree of purity.

Electronic tomography technology reveals three types of direct contact: point contact, electron-density nanostructure, and planar contact (11). In the human myocardium, cTCs engage in direct interactions with a diverse array of cell types. These comprise cardiomyocytes, which are responsible for myocardial contractility and relaxation. Fibroblasts, pivotal in maintaining cardiac extracellular matrix homeostasis and structural integrity. Endothelial cells, which line the vascular lumen and regulate vasomotor and permeability functions. Cardiac stem cells, endowed with self-renewal and multilineage differentiation potential. Mast cells, which play a significant role in cardiac immune surveillance and inflammatory responses (63, 64). Studies have confirmed frequent and close connections between vascular endothelial cells and cTCs through three different mechanisms (12, 65). Jeremiah Bernier Latmani et al. discovered that cTCs were extensively integrated into the subepithelial zone. Quantification of their cellular interactome indicated that the majority (around 70%) of direct cell contacts were either with other cells at the tip of the small intestinal villus. These findings position cTCs as perivascular cells uniquely situated at the villus tip, playing a crucial role in maintaining a polarized VEGFA signaling domain and promoting fenestrations within the nutrient-absorbing intestinal blood vessels (66).

cTCs act as intermediaries to enable communication between cells by facilitating exo- and endocytosis. During exocytosis, vesicles containing complex bioactive components act as important carriers for signal transmission between cTCs and other cells (67, 68). The vesicles secreted by cTCs can be categorized into three types according to their diameters: exosomes (45 ± 8 nm), ectosomes (128 ± 28 nm), and multivesicular cargo (1 ± 0.4 µm) (12, 69). Despite structural differences, these vesicles share similar biological functions. When the vesicle membrane degrades within the extracellular matrix, a diverse range of biological information is released and diffuses into the heart tissue, thereby affecting its function (70–72). cTCs also have endocytosis function, allowing them to uptake vesicles secreted by cardiac stem cells, cardiac myocytes, and endothelial cells and facilitate the retrogressive information transmission (12, 72). This phenomenon of information feedback has been experimentally verified using ink.

Studies have demonstrated that the number of cTCs in the region affected by acute myocardial infarction is significantly reduced. Studies have substantiated that, subsequent to the induction of myocardial infarction (MI) via ligation of the left anterior descending coronary artery (LAD), the synchronous intramyocardial injection of 10⁶ cTCs into both the infarcted myocardial region and the peri-infarct border zone can attenuate the infarct size, foster neovascularization, mitigate myocardial fibrotic remodeling, and ameliorate cardiac function 14 weeks after the intervention. This treatment may also improve cardiac function and reduce myocardial fibrosis (20, 61). The study demonstrates that cTCs can generate several microRNAs, which are well-known to play crucial regulatory roles in promoting the growth, migration, and angiogenic activity of endothelial cells. These microRNAs include miR-let-7e, miR-10a, miR-27b, miR-100, miR-126-3p, miR-130a, miR-143, miR-155, and miR-503 (22). Studies have verified that miR-25-5p, secreted by cTCs, can impede endothelial cell apoptosis. It achieves this by precisely targeting and silencing the cell death-inducing P53 target 1 (Cdip1) in coronary microcirculation endothelial cells. This mechanism is likely to be pivotal in the promotion of angiogenesis (23). During the neovascularization phase of acute myocardial infarction in rats, the number of cTCs in the border area of myocardial infarction increases significantly. Moreover, a large number of vesicles secreted by cTCs can be observed in the matrix between cTCs and endothelial cells. This study has identified significant changes in the number of cTCs after myocardial infarction. However, the reasons for the increase in the number of cTCs are still unclear. It remains unknown whether cTCs are migrating from the blood similar to inflammatory cells or if the signal transduction associated with myocardial cell infarction is stimulating the proliferation of cTCs. These cTCs and vesicles exhibit a high expression of VEGF and NOS2, indicating that cTCs may promote the formation of blood vessels in the border area of myocardial infarction by secreting vesicles (22). Cluster of differentiation 31(CD31), VEGF, PDGFR-β, and kruppel-like factor 4(KLF-4) were highly expressed (27, 86, 91). VEGF is widely acknowledged as the paramount factor in promoting angiogenesis, whereas PDGFR-β plays a crucial role in maintaining the stability of cardiac angiogenesis. Additionally, KLF-4 is a crucial regulatory factor that promotes endothelial cell proliferation and differentiation. Based on these factors, it can be inferred that cTCs, which produce these factors, play a crucial role in sustaining the growth of blood vessels in the heart, as shown in Figure 3.

Thrombosis is a significant mechanism that leads to IHD. The exocrine secretion of cTCs contains various miRNAs that regulate the thrombosis process at different targets. It is a glycoprotein on the surface of the endothelial cell membrane. Studies have demonstrated that miR-92a has the ability to enhance the expression of Kruppel-like factor 2 (KLF2) and TM in human uveal epithelial cells through its binding to KLF2. Therefore, the down-regulation of miR-92a may be connected to thrombosis (92, 93). The levels of miR-21, miR-409-3p, miR-432, and miR-150 were significantly lower in patients with atrial fibrillation compared to the control group. Nonetheless, subsequent to radiofrequency ablation, the levels of these microRNAs significantly increased, indicating that they may possess a pivotal role in the process of thrombosis (94–96). The expression of miR-126 was significantly decreased in acute myocardial infarction, which is one of the markers of endothelial cell injury. This suggests that the reduced expression of miR-126 may increase the risk of thrombosis (97, 98). Tissue factor (TF) is a promoter of the exogenous coagulation pathway. However, miR-451a inhibits the expression of coagulation factors such as TF, factor X coagulant (FXa), and von willebrand factor (vWF) by targeting the IL6R/STAT/TF pathway. Simultaneously, miR-451a significantly up-regulates the expression of anticoagulant factors such as antithrombin III (ATIII), tissue factor pathway inhibitor (TFPI), and tissue plasminogen activator (tPA). This helps to suppress the formation of intravascular thrombosis. Therefore, miR-451a is one of the important miRNAs that inhibit thrombosis (99). Thromboxane A2 (TXA2) promotes platelet aggregation while prostaglandin-I-2 (PGI2) inhibits it. The balance between TXA2 and PGI2 is crucial in preventing both thrombosis and bleeding. Research has indicated that the expression of miR-26a-5p is significantly decreased in patients with coronary heart disease. Upon treatment with a miR-26a-5p inhibitor, the serum levels of TXA2, endothelin-1 (ET-1), and angiotensin II (Ang II) were upregulated, whereas the expression of PGI2 and eNOS were downregulated. Consequently, this led to reduced endothelial cell activity and increased apoptosis. The mechanism behind this is related to the inhibition of the PI3K/AKT signal. Therefore, miR-26a-5p expression is a crucial factor in thrombosis (100). However, this study was unable to identify drugs or key regulatory factors that upregulate the expression of miR-26a-5p in cTCs, thereby lacking more convincing evidence for the inhibitory effect of cTCs on thrombosis. According to the study, during transcription, the expression of miR-301a/miR-454 is downregulated by the co-regulation of hypoxia-inducible factor-1α (HIF-1α) and peroxisome proliferator-activated receptor-α (PPAR-α). The low expression levels of miR-301a/miR-454 can lead to an increase in endothelin-1 (ET-1) and plasminogen activator inhibitor-1 (PAI-1), suggesting that miR-301a/miR-454 may play a regulatory role in thrombosis (101).

MiR-130a, miR-124, miR-155 and miR-499 are thought to play crucial roles in regulating the permeability of microcirculatory vessels, the formation of edema, and the expulsion of inflammatory factors. Exosomes secreted by cTCs are rich in this miRNA, which allows them to regulate the barrier function of microvasculature by transferring these miRNAs to endothelial cells. Studies have shown that miR-130a, produced by endothelial cells exposed to ischemia, disrupts the integrity of the blood-brain barrier. This occurs through the regulation of the transcription factor homeobox A5 (HOXA5), which is related to the expression of the tight junction protein occludin. However, the administration of a miR-130a antagonist can improve the permeability of the blood-brain barrier and lead to edema in brain tissue. Consequently, miR-130a is a factor that can cause enhanced microvascular permeability (102, 103). miR-124 has a specific effect on inhibiting exudation and inflammatory reactions. It functions as an anti-inflammatory agent by regulating the IL-6/TNF-α signal transduction process. Additionally, its expression is up-regulated by the anti-inflammatory factors IL-4 and IL-13. However, miR-124 can also increase the production of reactive oxygen radicals by inhibiting PI3K/AKT signal transduction, which can lead to the apoptosis of endothelial cells (104). Therefore, miR-124 may have a dual impact on IHD. On one hand, it can reduce inflammatory exudation and suppress the inflammatory response, on the other hand, it may accelerate the damage to endothelial cells (105). Research has shown that miR-155 plays a crucial role in regulating microvascular barrier function and inflammatory response. By regulating the expression of tight junction protein zonula occludens-1 (ZO-1) and eNOS in endothelial cells, specific inhibitors of miR-155 can help to maintain microvascular barrier function and regulate vascular diameter (106, 107). The study revealed that the inhibition of miR-155 expression has varying impacts on the regulatory function of the inflammatory response over time. In the early stage (7 days), inhibiting JAK/STAT signal transduction can suppress the inflammatory response. In the late stage, miR-155's key target, CCAAT/enhancer binding protein β (C/EBP β), is up-regulated to enhance the inflammatory response, which facilitates the removal of necrotic tissue and promotes tissue repair (108, 109). miR-499 is an important marker of myocardial injury, and its expression is closely related to the prognosis of cardiovascular disease. Studies have found that the programmed cell death 4(PDCD4) protein can inhibit the NF-kB/TNF-α signal, reducing the inflammatory response. However, miR-499 counters this effect by targeting PDCD4, inducing inflammatory damage to endothelial cells (110). Studies indicate that the α7 nicotinic acetylcholine receptor (α7-nAchR) is expressed by endothelial cells and functions as a cholinergic anti-inflammatory pathway regulator, inhibiting the release of inflammatory factors (111–113). In acute myocardial infarction, endothelial cells internalize miR-499 and target α7-nAChR, significantly enhancing the inflammatory response of endothelial cells (114). The following miRNAs play a regulatory role in vascular inflammation: miR-146a, miR-217, miR-34a, miR-126, miR-21, miR210, and miR-181b (115, 116). It should also be noted that in addition to miRNA these mtDNA in cTCs were often released into the microenvironment and played an important role in the development of different types of inflammatory diseases, including acute and chronic ischemic diseases, traumatic brain injury, and infectious diseases (117). cTCs exocrine secretion contains multiple miRNAs that can regulate microvascular inflammatory exudation, playing an intervention role in IHD, as shown in Figure 4.

Vascular diastolic and systolic function disorders are major contributors to IHD. ET-1, Angiotensin II (Ang II), vasopressin, and epinephrine are vasoconstrictive substances, while NO, prostacyclin (PGI2), endothelial hyperpolarizing factor (EDHF), and bradykinin have vasodilatory effects. Currently, ET-1, NO, PGI2, and EDHF are considered crucial regulators of endothelium-dependent vasodilation or vasoconstriction dysfunction, and their secretion and formation are closely linked to endothelial cell function. Research indicates that the upregulation of miR-21a-3p expression plays a significant role in vasodilation, and that silencing miR-21a-3p expression can markedly reduce the expression of eNOS, a crucial factor in affecting NO synthesis in endothelial cells (118). The study discovered that miR-21 can impact the expression of both ET-1 and eNOS by regulating the MAPK/ET-1 and PTEN/AKT/eNOS signal pathways. This suggests that miR-21 plays a role in controlling vasodilation and contraction functions by affecting the downstream targets of these pathways (119, 120). The expression of miR-92a is positively correlated with the level of ET-1, while the expression of miRNA-1 is negatively correlated with ET-1 (121). This indicates that maintaining a balance between miR-92a and miRNA-1 expression is vital for vasoconstriction. Although this study implies that maintaining the balance of miR-92a/miRNA-1 is crucial for regulating the expression of ET-1, a key regulator of vasodilation, the effectiveness of this balance could not be assessed in vivo using more objective methods such as magnetic resonance imaging techniques. Moreover, the study failed to propose key factors that regulate the balance of miR-92a/miRNA-1. Research has shown that overexpression of miR-124 and miR-34c can increase PGI2 expression, resulting in vasodilation. This mechanism is related to the regulation of the JAK2/STAT3 signal pathway (122).

The main pathological changes that occur during vascular remodeling are caused by the deposition of collagen fibers and the reduction of vascular smooth muscle cells. In this process, cTCs express type IV collagen, matrix metalloprotein-3, -9, -10 (MMP-3, -9, -10), which play a crucial role in the formation and degradation of the vascular basement membrane. Type IV collagen is the most important component of the vascular basement membrane (59, 123). According to the study, the skin tissue of psoriasis patients showed significant damage to their microvascular structure, and there was a considerable reduction in the number of TCs. However, after effective treatment, the vascular remodeling significantly improved, and the number of TCs increased, indicating that TCs play a vital role in the regulation of vascular remodeling (124). The study found that miR-197-3p can inhibit extracellular matrix degradation and increase vWF expression by targeting tissue inhibitor of metallo proteinase 3 (TIMP3), thus promoting vascular remodeling and thrombosis (125, 126). Studies have indicated that miR-21a-3p in cTCs increases expression of matrix metalloproteinase-2 (MMP-2) by activating the PI3K/AKT/mTOR pathway. MMP-2 is a vital factor in the degradation of the vascular basement membrane (118). The study revealed that miR-92a downregulated alpha-smooth muscle actin (α-SMA), smoothelin (SMTN), and calponin (CALP), while upregulating fibronectin (FN), osteopontin (OPN), and thrombospondin (TSP). These factors play a crucial role in the phenotypic transformation of vascular smooth muscle cells and are important contributors to the acceleration of arteriosclerosis (127). Signal transduction inhibitor 1(SOCS1) functions as a cytokine signaling inhibitor capable of negatively modulating the JAK/STAT signaling pathway. MiR-155-5p activates the JAK2/STAT3 signaling pathway through the inhibition of SOCS1 expression, subsequently promoting the expression of vascular endothelial growth factor A (VEGFa), matrix metalloproteinase-9 (MMP9) and fibroblast growth factor 2 (FGF2). This regulatory effect plays a crucial role in processes such as inflammatory responses, immune responses, and vascular remodeling (128).