Endothelial structure contributes to heterogeneity in brain capillary diameter.

The high metabolic demand of brain tissue is supported by a constant supply of blood flow through dense microvascular networks. Capillaries are the smallest class of vessels in the brain and their lumens vary in diameter between ~2 and 5 µm. This diameter range plays a significant role in optimizing blood flow resistance, blood cell distribution, and oxygen extraction. The control of capillary diameter has largely been ascribed to pericyte contractility, but it remains unclear if the architecture of the endothelial wall also contributes to capillary diameter. Here, we use public, large-scale volume electron microscopy data from mouse cortex (MICrONS Explorer, Cortical mm3) to examine how endothelial cell number, endothelial cell thickness, and pericyte coverage relates to microvascular lumen size. We find that transitional vessels near the penetrating arteriole and ascending venule are composed of two to six interlocked endothelial cells, while the capillaries intervening these zones are composed of either one or two endothelial cells, with roughly equal proportions. The luminal area and diameter are on average slightly larger with capillary segments composed of two interlocked endothelial cells vs one endothelial cell. However, this difference is insufficient to explain the full range of capillary diameters seen in vivo. This suggests that both endothelial structure and other influences, including pericyte tone, contribute to the basal diameter and optimized perfusion of brain capillaries.

Endothelial structure contributes to heterogeneity in brain capillary diameter.

The high metabolic demand of brain tissue is supported by a constant supply of blood through dense microvascular networks. Capillaries are the smallest class of vessels and vary in diameter between ∼2 to 5 µm in the brain. This diameter range plays a significant role in the optimization of blood flow resistance, blood cell distribution, and oxygen extraction. The control of capillary diameter has largely been ascribed to pericyte contractility, but it remains unclear if endothelial wall architecture also contributes to capillary diameter heterogeneity. Here, we use public, large-scale volume electron microscopy data from mouse cortex (MICrONS Explorer, Cortical MM^3) to examine how endothelial cell number, endothelial cell thickness, and pericyte coverage relates to microvascular lumen size. We find that transitional vessels near the penetrating arteriole and ascending venule are composed of 2 to 5 interlocked endothelial cells, while the numerous capillary segments intervening these zones are composed of either 1 or 2 endothelial cells, with roughly equal proportions. The luminal area and diameter is on average slightly larger with capillary segments composed of 2 interlocked endothelial cells versus 1 endothelial cell. However, this difference is insufficient to explain the full range of capillary diameters seen in vivo. This suggests that both endothelial structure and other influences, such as pericyte tone, contribute to the basal diameter and optimized perfusion of brain capillaries.

Regenerative potential and limitations in a zebrafish model of hyperglycemia-induced nerve degeneration.

BACKGROUND: Previous work from our lab has described a model of motor nerve degeneration in hyperglycemic zebrafish larvae which resembles mammalian models of diabetic peripheral neuropathy (DPN). Here, we optimized the hyperglycemic-induction protocol, characterized deficits in nerve structure and behavioral function, and then examined the regenerative potential following recovery from the hyperglycemic state. RESULTS: In agreement with our previous work, hyperglycemia induced motor nerve degeneration and behavioral deficits. However, the optimized protocol initiated disruption of tight junctions within the blood-nerve barrier, a phenotype apparent in mammalian models of DPN. Following a 10-day recovery period, regeneration of motor nerve components was apparent, but behavioral deficits persisted. We next examined the effect of hyperglycemia on the musculoskeletal system and found subtle deficits in muscle that resolved following recovery, and robust deficits in the skeletal system which persisted following recovery. CONCLUSION: Here we optimized our previous model of hyperglycemia-induced motor nerve degeneration to more closely align with that observed in mammalian models and then characterized the regenerative potential following recovery from hyperglycemia. Notably, we observed striking impairments to skeletal development, which underscores the global impact hyperglycemia has across systems, and provides a framework for elucidating molecular mechanisms responsible for regenerative events moving forward.