**8. Intercellular communication**

Thus, it was demonstrated that the cellular network is disintegrated in the proteoglycan-rich layer of atherosclerotic lesions [67]. Eventually, this disintegration results in complete sepa‐ ration of cells in an atherosclerotic plaque. It is an established fact that the regulation of cells forming highly differentiated tissue systems occurs via specialized cell-to-cell contacts, gap junctions [68, 69]. It was demonstrated that these contacts play an important role in the regulation of tissue homeostasis, providing the transport of cell metabolites, second messen‐ gers, and other biologically active molecules from cell to cell without entering the extracellular space. The presence of these specialized contacts is a specific feature of the differentiated cell systems with a high degree of intercellular integration [68-73]. Stellate shape of intimal cells and their interaction via the cellular processes may substantially contribute to the vascular wall regulation. It can be hypothesized that functional disturbances in gap junctions are one of the causes of atherosclerosis-related disintegration of cellular networks formed by the proteoglycan-rich layer intimacytes [73].

The degree of intercellular communication via gap junctions can be assessed by expression of proteins forming these contacts. Connexin 43 (Cx43) is the major protein of these contacts. This protein is localized on cell surfaces in so-called connexin plaques [73]. A primary culture of aortic cells was used to elucidate the causes of reduced intercellular communication in atherosclerotic lesions. In addition to the identification of Cx43, another approach can be employed in a cell culture, namely, the transfer of fluorescent dye from the injected cell to neighboring cells. Fluorescent dye is specifically distributed only via gap junctions, and the rate of the communication is evaluated by the number of contacting fluorescent cells. The rate of intercellular communication in cell cultures with various densities has been estimated [73]. It was revealed that both approaches correlated very closely with each other. It was found that the intensity of intercellular communication in cultures derived from grossly normal areas is 1.5-fold higher than that in cultures obtained from atherosclerotic lesions [73].

bipolar elongated shape characteristic of medial smooth muscle cells. In the muscular-elastic

A continuous vertical gradient in the ratio between the number of stellate subendothelial cells and typical elongated smooth muscle cells has been discovered [67]. The number of elongated cells decreases from the muscular-elastic layer to the endothelium, while the number of

In atherosclerotic lesions, the cellular system of the intima undergoes considerable changes. In fatty streaks, many stellate cells are generally laden with lipids [14, 25, 66]. This may account for an increase in their dimensions and formation of surface bleb-like protrusions by lipid droplets and vesicles. Vesicles in the extracellular space were also found; this suggests that these vesicles are propagated by gemmation (budding) from the surface of the cells and cell processes. Vesicle gemmation from the ends of the cell processes can obviously lead to the degradation of intercellular contacts and dissociation of the common network. In atheroscler‐ otic plaques, changes in the cell system are more pronounced. In the superficial layers of the connective tissue cap, stellate cells are always settled as separate cells or small groups. Sometimes, these cells contain lipid inclusions. In deep layers of the intima, the number of processed cells increases, but they do not form a network. Interestingly, a three-dimensional cellular network typical of uninvolved intima was found in the intima next to the plaque

Thus, it was demonstrated that the cellular network is disintegrated in the proteoglycan-rich layer of atherosclerotic lesions [67]. Eventually, this disintegration results in complete sepa‐ ration of cells in an atherosclerotic plaque. It is an established fact that the regulation of cells forming highly differentiated tissue systems occurs via specialized cell-to-cell contacts, gap junctions [68, 69]. It was demonstrated that these contacts play an important role in the regulation of tissue homeostasis, providing the transport of cell metabolites, second messen‐ gers, and other biologically active molecules from cell to cell without entering the extracellular space. The presence of these specialized contacts is a specific feature of the differentiated cell systems with a high degree of intercellular integration [68-73]. Stellate shape of intimal cells and their interaction via the cellular processes may substantially contribute to the vascular wall regulation. It can be hypothesized that functional disturbances in gap junctions are one of the causes of atherosclerosis-related disintegration of cellular networks formed by the

The degree of intercellular communication via gap junctions can be assessed by expression of proteins forming these contacts. Connexin 43 (Cx43) is the major protein of these contacts. This protein is localized on cell surfaces in so-called connexin plaques [73]. A primary culture of aortic cells was used to elucidate the causes of reduced intercellular communication in atherosclerotic lesions. In addition to the identification of Cx43, another approach can be employed in a cell culture, namely, the transfer of fluorescent dye from the injected cell to neighboring cells. Fluorescent dye is specifically distributed only via gap junctions, and the

layer, densely packed cells form strata oriented at a small angle to each other [67].

network-forming stellate cells increases.

214 Muscle Cell and Tissue

**8. Intercellular communication**

proteoglycan-rich layer intimacytes [73].

shoulders displaying no visible atherosclerosis-related changes.

The presence of lipid-laden cells resembling so-called foam cells was a specific feature of cultures derived from atherosclerotic lesions [73]. Assuming that there is a relationship between the content of intracellular lipids and the rate of the intercellular communication, fluorescent dye was injected into cells with and without visual lipid inclusions. The rate of gap junctional communication of cells without lipids was similar to that of cells cultured from grossly normal areas [73]. The rate of communication of foam cells was twofold lower than that of lipid-free cells. The number of Cx43 plaques per lipid-laden cell was lower than per cell without lipids [73]. It can be suggested that lipid accumulation is a possible cause of reduced intercellular communication in the intimal cell system.

On the basis of the above data, it can be concluded that stellate cells are the principal cell type of the proteoglycan-rich layer. Stellate cells of subendothelial intima differ from typical medial smooth muscle cells. In contrast to elongated smooth muscle cells, they have several long processes capable of forming a network. Stellate cells have poor contractile organelles but possess a well-developed rough endoplasmic reticulum. These cells express a number of markers (pericyte antigens 3G5 and 2A7, macrophage antigen CD86, scavenger receptor) that are not expressed by typical smooth muscle cells. These markers may determine functional peculiarities of stellate cells. The number of stellate cells increases in arteriosclerotic lesions and strongly correlates with the major manifestations of atherosclerosis. In uninvolved intima, the cells of the proteoglycan-rich layer contact with each other by their processes forming a three-dimensional network. In atherosclerotic lesions, the rate of intercellular communication decreases and the contacts between cells are impaired, presumably as a result of lipid accu‐ mulation.
