Drebrin at Junctional Plaques

Cooperative cell-cell actin network remodeling to perform Gap junction endocytosis

BACKGROUND

The endocytosis of Gap junction plaques (GJP) requires cytoskeletal forces to internalize such large membranous structures. Actin, which partners the connexin proteins constituting Gap junctions and is located close to Annular Gap Junctions (AGJ), could be actively involved in this physiological process.

RESULTS

Electron Microscopy and Light Microscopy images, associated with time-lapse analysis and 3D reconstruction, used at high resolution and enhanced using ImageJ based software analysis, revealed that: i) actin cables, originating from Donor cells, insert on the edge of GJP and contribute to their invagination, giving rise to AGJ, whereas actin cables on the Acceptor cell side of the plaque are not modified; ii) actin cables from the Donor cell are continuous with the actin network present over the entire GJP surface. These actin cables fuse at a single point distant from the plaque, which then detaches itself from the membrane, condensing to form an actin mass during the final internalization process; iii) the Acceptor cell participates in the last step of the endocytic invagination process by forming an annular actin structure known as an actin ring.

CONCLUSIONS

Together, these data suggest that the endocytosis of GJP is an example of a unique cooperative mechanism between the Donor (the traction of its actin cables) and the Acceptor cells (forming the actin ring).

The Significant Role of the Microfilament System in Tumors

Actin is the structural protein of microfilaments, and it usually exists in two forms: monomer and polymer. Among them, monomer actin is a spherical molecule composed of a polypeptide chain, also known as spherical actin. The function of actin polymers is to produce actin filaments, so it is also called fibroactin. The actin cytoskeleton is considered to be an important subcellular filament system. It interacts with numerous relevant proteins and regulatory cells, regulating basic functions, from cell division and muscle contraction to cell movement and ensuring tissue integrity. The dynamic reorganization of the actin cytoskeleton has immense influence on the progression and metastasis of cancer as well. This paper explores the significance of the microfilament network, the dynamic changes of its structure and function in the presence of a tumor, the formation process around the actin system, and the relevant proteins that may be target molecules for anticancer drugs so as to provide support and reference for interlinked cancer treatment research in the future.

Phylogenic Determinants of Cardiovascular Frailty, Focus on Hemodynamics and Arterial Smooth Muscle Cells

The evolution of the circulatory system from invertebrates to mammals has involved the passage from an open system to a closed in-parallel system via a closed in-series system, accompanying the increasing complexity and efficiency of life’s biological functions. The archaic heart enables pulsatile motion waves of hemolymph in invertebrates, and the in-series circulation in fish occurs with only an endothelium, whereas mural smooth muscle cells appear later. The present review focuses on evolution of the circulatory system. In particular, we address how and why this evolution took place from a closed, flowing, longitudinal conductance at low pressure to a flowing, highly pressurized and bifurcating arterial compartment. However, although arterial pressure was the latest acquired hemodynamic variable, the general teleonomy of the evolution of species is the differentiation of individual organ function, supported by specific fueling allowing and favoring partial metabolic autonomy. This was achieved via the establishment of an active contractile tone in resistance arteries, which permitted the regulation of blood supply to specific organ activities via its localized function-dependent inhibition (active vasodilation). The global resistance to viscous blood flow is the peripheral increase in frictional forces caused by the tonic change in arterial and arteriolar radius, which backscatter as systemic arterial blood pressure. Consequently, the arterial pressure gradient from circulating blood to the adventitial interstitium generates the unidirectional outward radial advective conductance of plasma solutes across the wall of conductance arteries. This hemodynamic evolution was accompanied by important changes in arterial wall structure, supported by smooth muscle cell functional plasticity, including contractility, matrix synthesis and proliferation, endocytosis and phagocytosis, etc. These adaptive phenotypic shifts are due to epigenetic regulation, mainly related to mechanotransduction. These paradigms actively participate in cardio-arterial pathologies such as atheroma, valve disease, heart failure, aneurysms, hypertension, and physiological aging.

Connexins in the control of vasomotor function

Vascular endothelial cells, as well as smooth muscle cells, show heterogeneity with regard to their receptor expression and reactivity. For the vascular wall to act as a functional unit, the various cells' responses require integration. Such an integration is not only required for a homogeneous response of the vascular wall, but also for the vasomotor behaviour of consecutive segments of the microvascular arteriolar tree. As flow resistances of individual sections are connected in series, sections require synchronization and coordination to allow effective changes of conductivity and blood flow. A prerequisite for the local coordination of individual vascular cells and different sections of an arteriolar tree is intercellular communication. Connexins are involved in a dual manner in this coordination. (i) By forming gap junctions between cells, they allow an intercellular exchange of signalling molecules and electrical currents. In particular, the spread of electrical currents allows for coordination of cell responses over longer distances. (ii) Connexins are able to interact with other proteins to form signalling complexes. In this way, they can modulate and integrate individual cells' responses also in a channel-independent manner. This review outlines mechanisms allowing the vascular connexins to exert their coordinating function and to regulate the vasomotor reactions of blood vessels both locally, and in vascular networks. Wherever possible, we focus on the vasomotor behaviour of small vessels and arterioles which are the main vessels determining vascular resistance, blood pressure and local blood flow.