Prolonged systemic hyperglycemia does not cause pericyte loss and permeability at the mouse blood-brain barrier

Abstract

Diabetes mellitus is associated with cognitive impairment and various central nervous system pathologies such as stroke, vascular dementia, or Alzheimer’s disease. The exact pathophysiology of these conditions is poorly understood. Recent reports suggest that hyperglycemia causes cerebral microcirculation pathology and blood-brain barrier (BBB) dysfunction and leakage. The majority of these reports, however, are based on methods including in vitro BBB modeling or streptozotocin-induced diabetes in rodents, opening questions regarding the translation of the in vitro findings to the in vivo situation, and possible direct effects of streptozotocin on the brain vasculature. Here we used a genetic mouse model of hyperglycemia (Ins2AKITA) to address whether prolonged systemic hyperglycemia induces BBB dysfunction and leakage. We applied a variety of methodologies to carefully evaluate BBB function and cellular integrity in vivo, including the quantification and visualization of specific tracers and evaluation of transcriptional and morphological changes in the BBB and its supporting cellular components. These experiments did neither reveal altered BBB permeability nor morphological changes of the brain vasculature in hyperglycemic mice. We conclude that prolonged hyperglycemia does not lead to BBB dysfunction, and thus the cognitive impairment observed in diabetes may have other causes.

Pericyte Bridges in Homeostasis and Hyperglycemia: Reconsidering Pericyte Dropout and Microvascular Structures

“…Our results also reveal shortcomings in the classical retinal digest assay that has been cited as support for pericyte drop-out in diabetic conditions 20 , and they suggest that pericyte loss as a causative factor in diabetic vasculopathies needs to be reexamined, as it has already in the Akita mouse model 11 . Our analysis of immunostained retinas revealed that up to 50% of all pericyte somas were associated with a basement membrane bridge (combination of pericyte bridges and basement membrane bridged pericytes), which would have been miscounted as endothelial somas 47,48 in the retinal digest assay and potentially accounts for the approximately 30% 20 loss in pericyte density observed with this assay in diabetes and Ang2 stimulation.…”

“…This rapid change in pericyte bridges was recapitulated by injection of recombinant Ang2 and PDGF-BB, both of which are cytokines upregulated in diabetes 20,21 . Elevation of pericyte bridges in Akita mice 11 provides further evidence that high blood sugar could be a short-term stimulus for enrichment of this pericyte phenotype.…”

“…The published literature has established the existence of pericyte bridge-like cells and basement membrane bridges in homeostasis and documented their elevated abundance in models of diabetes [10][11][12][13] . Here, we sought to determine if these cell and cell-free structures that span capillaries in the murine and human retina are reversibly modulated with stimuli relevant to diabetes and when a gene that is associated with cell migration 24,40 is ablated from pericytes.…”

“…However, some studies have observed pericyte-like cells bridging across two or more adjacent capillaries in both homeostatic 9 and pathological conditions such as diabetes, where their frequency is elevated 10 . These studies have framed the existence of pericyte-like bridges as evidence of pericyte detachment, where it is assumed that a fully-attached pericyte migrates (or begins to migrate) away from the capillary on which it resides and extends cell processes or its entire cell soma to form a bridge from one capillary to another [10][11][12][13] . Previous research has indicated that these bridging cells can colocalize with basement membrane structures that also span across, or bridge, adjacent capillaries 9,14 .…”

Pericyte Bridges in Homeostasis and Hyperglycemia

“…One hypothesis is that these pericyte-like bridges form as a result of pericyte detachment (9)(10)(11)(12), where it is assumed that a fully attached pericyte migrates (or begins to migrate) away from the capillary on which it resides and extends cell processes or its entire cell soma to form a bridge from one capillary to another. Alternatively, other cell types may potentially give rise to these bridging cells or contribute to these basement membrane bridges (8).…”