Neurovascular Unit: a Focus on Pericytes

Abstract

The blood-brain barrier (BBB) is a highly specialized system that controls the exchanges between the blood and the central nervous system (CNS). This barrier shields the CNS from toxic substances in the blood and provides nutrients to CNS, thus playing an essential role in the maintenance of homeostasis. The anatomical basis of the BBB is formed by the endothelial cells of brain microvasculature, with elaborated tight and adherens junctions, which together with pericytes, the basement membrane, and astrocytes, as well as neurons, microglia and oligodendrocytes form the neurovascular unit. The interaction between all these components guarantees a proper environment for neural function and a restricted permeability and transport. Pericytes were initially reported by Rouget in 1873 and since then they have been recognized as an important component of the BBB, despite the difficulty of their identification. Diverse functions have been assigned to pericytes, including a role in BBB properties, hemostasis, and angiogenesis, as well as a contractile, immune, and phagocytic function. These cells are also seen like multipotent cells and so with a great potential for therapy. Here, we review the neurovascular unit composition and the interplay between the diverse components, addressing pericytes with a particular detail.

Vascular Remodelling is Impaired in Parkinson Disease

“…Expressions of VEGF in brain tissue, particularly which in astrocytes and blood vessels are commonly used for indicating the ability in vascular remodelling. This is supported by similar reports that the VEGF was diffusely expressed on vascular walls, extracellular spaces, neurons and astrocytes [7,[40][41][42]. By analysing the overall density of the VEGF expression, we found a general reduction of VEGF in the MFG of the PD cases.…”

Traumatic Penumbra: Opportunities for Neuroprotective and Neurorestorative Processes

“…Another cell of the NVU, the pericyte, has been recognized as a component of the BBB more than a century ago [127]. Functions attributed to pericytes in the CNS include regulation of the BBB permeability, angiogenesis, clearance of toxic metabolites, and capillary hemodynamic responses [128].…”

Endocannabinoids in cerebrovascular regulation

“…These cells were shown to control capillary diameter by constricting the vascular wall, and this effect may significantly influence capillary blood flow during reperfusion after cerebral ischemia (176,258). Pericytes express receptors for vasoconstrictor substances such as angiotensin II, endothelin-1 (ET-1), and vasopressin, which mediate reduction of capillary diameter and blood flow (200). In contrast, NO causes the relaxation of pericytes through cyclic guanosine monophosphate production (85).…”

“…In contrast, NO causes the relaxation of pericytes through cyclic guanosine monophosphate production (85). Furthermore, prostacyclin and adenosine were also shown to relax pericytes (200), and the consequent decrease in cerebrovascular resistance may significantly contribute to neurovascular coupling (67). In fact, pericytes may play a major role in the very fine spatial distribution of blood flow to small groups of active neurons by increasing the diameter of nearby capillaries (200).…”