Protoplasmic Perivascular Astrocytes Play a Crucial Role in the Development of Enlarged Perivascular Spaces in Obesity, Metabolic Syndrome, and Type 2 Diabetes Mellitus

Abstract

Astrocytes (ACs) are the most abundant cells in the brain and, importantly, are the master connecting and communicating cells that provide structural and functional support for brain cells at all levels of organization. Further, they are recognized as the guardians and housekeepers of the brain. Protoplasmic perivascular astrocyte endfeet and their basal lamina form the delimiting outermost barrier (glia limitans) of the perivascular spaces in postcapillary venules and are important for the clearance of metabolic waste. They comprise the glymphatic system, which is critically dependent on proper waste removal by the pvACef polarized aquaporin-4 water channels. Also, the protoplasmic perisynaptic astrocyte endfeet (psACef) are important in cradling the neuronal synapses that serve to maintain homeostasis and serve a functional and supportive role in synaptic transmission. Enlarged perivascular spaces (EPVS) are emerging as important aberrant findings on magnetic resonance imaging (MRI), and are associated with white matter hyperintensities, lacunes, and aging, and are accepted as biomarkers for cerebral small vessel disease, increased obesity, metabolic syndrome, and type 2 diabetes. Knowledge is exponentially expanding regarding EPVS along with the glymphatic system, since EPVS are closely associated with impaired glymphatic function and waste removal from the brain to the cerebrospinal fluid and systemic circulation. This review intends to focus on how the pvACef play a crucial role in the development of EPVS.

Keywords

• blood–brain barrier
• endothelial glycocalyx
• enlarged perivascular spaces
• metabolic syndrome
• neuroinflammation
• neurovascular unit