Early Radiation-Induced Endothelial Cell Loss and Blood–Spinal Cord Barrier Breakdown in the Rat Spinal Cord

Abstract

Using a rat spinal cord model, this study was designed to characterize radiation-induced vascular endothelial cell loss and its relationship to early blood-brain barrier disruption in the central nervous system. Adult rats were given a single dose of 0, 2, 8, 19.5, 22, 30 or 50 Gy to the cervical spinal cord. At various times up to 2 weeks after irradiation, the spinal cord was processed for histological and immunohistochemical analysis. Radiation-induced apoptosis was assessed by morphology and TdT-mediated dUTP nick end labeling combined with immunohistochemical markers for endothelial and glial cells. Image analysis was performed to determine endothelial cell and microvessel density using immunohistochemistry with endothelial markers, namely endothelial barrier antigen, glucose transporter isoform 1, laminin and zonula occludens 1. Blood-spinal cord barrier permeability was assessed using immunohistochemistry for albumin and (99m)Tc-diethylenetriamine pentaacetic acid as a vascular tracer. Endothelial cell proliferation was assessed using in vivo BrdU labeling. During the first 24 h after irradiation, apoptotic endothelial cells were observed in the rat spinal cord. The decrease in endothelial cell density at 24 h after irradiation was associated with an increase in albumin immunostaining around microvessels. The decrease in the number of endothelial cells persisted for 7 days and recovery of endothelial density was apparent by day 14. A similar pattern of blood-spinal cord barrier disruption and recovery of permeability was observed over the 2 weeks, and an increase in BrdU-labeled endothelial cells was seen at day 3. These results are consistent with an association between endothelial cell death and acute blood-spinal cord barrier disruption in the rat spinal cord after irradiation.

Microglia in the CNS: Immigrants from another world

“…First, lethal irradiation could have significant influences on the CNS tissue. Indeed, it had been reported that irradiation affects the integrity of the BBB (Diserbo et al, 2002;Yuan et al, 2003) and the expression of tight junction proteins (Kaya et al, 2004), and also induced apoptosis of endothelial cells (Li et al, 2004). An alternative explanation could have been the injection of BM cells by which myeloid precursors gain nonphysiological access to the circulation and thereby facilitate phagocyte generation from the blood stream.…”

Cerebral microvascular rarefaction induced by whole brain radiation is reversible by systemic hypoxia in mice

“…In animal studies, radiation therapy has been shown to induce dose-dependent endothelial apoptosis (30) and disruption of the blood-brain barrier (31), thickening and vacuolation of the vascular basement membrane (25), vascular rarefaction (7), and cognitive deficits (6,46). To sustain neuronal activity and normal brain function, blood vessel integrity must be preserved to maintain a consistent supply of oxygen, nutrients, and growth factors and provide efficient removal of waste products from cells.…”

Origin of Microglia: Current Concepts and Past Controversies

“…However, Ajami further clarified that, although irradiation is required for donor cells to engraft, it is not sufficient; another important but often overlooked requirement is the artificial and concomitant introduction of a critical number of donor BM cells into the blood circulation (where they are not normally found). This, in conjunction with the inflammation of the BBB caused by irradiation, creates the unique nonphysiological situation that is required for the BM-to-microglia pathway to prevail (Diserbo et al 2002;Li et al 2004;Capotondo et al 2012). Taking this work further, the same group recently used a similar approach, combining parabiosis and myeloablation, to show that recruited monocytes do not persist in the CNS and, therefore, even under these specific conditions, do not stably contribute to the resident microglial pool (Ajami et al 2011).…”