The brain is sensitive to aging-related morphological changes, where many neurodegenerative diseases manifest accompanied by a reduction in memory. The hippocampus is especially vulnerable to damage at an early stage of aging. The present transmission electron microscopy study examined the synapses and synaptic mitochondria of the CA1 region of the hippocampal layer in young-adult and old rats by means of a computer-assisted image analysis technique. Comparing young-adult (10 months of age) and old (22 months) male Fischer (CDF) rats, the total numerical density of synapses was significantly lower in aged rats than in the young adults. This age-related synaptic loss involved degenerative changes in the synaptic architectonic organization, including damage to mitochondria in both pre- and post-synaptic compartments. The number of asymmetric synapses with concave curvature decreased with age, while the number of asymmetric synapses with flat and convex curvatures increased. Old rats had a greater number of damaged mitochondria in their synapses, and most of this was type II and type III mitochondrial structural damage. These results demonstrate age-dependent changes in the morphology of synaptic mitochondria that may underlie declines in age-related synaptic function and may couple to age-dependent loss of synapses.

Background Ischemic stroke is a major cause of death among patients with systemic hypertension. The narrowing of the brain vascular lumen increases the incidence of stroke and the formation of hyalinosis lesion is an irreversible process that occurs in the late stage of the disease and contributes to the vascular narrowing and stroke. Understanding pathologic mechanisms of brain vascular hyalinosis, thus, should contribute to the development of new therapeutic agents that inhibits and/or reverse the formation of hyalinosis, thereby reducing the incidence of ischemic stroke. Despite the clinical importance of this lesion, properties of brain vascular hyalinosis have not been well investigated. Thus, the present study performed detailed histological examinations of the hyalinosis lesions of postmortem brain vascular tissues of human patients who died of ischemic stroke due to systemic hypertension. Methods & Results Hematoxylin and eosin staining, as well as periodic acid‐Schiff staining, showed the presence of vascular hyalinosis in patient brain tissues. In these lesions, the protein organization of the extracellular matrix was changed, the number and size of smooth muscle cells were altered, and plasma proteins, such as apolipoprotein E and fibrin, infiltrated into the vessel wall. Signs of oxidative stress and lipid peroxidation were also found. These changes are pronounced at the loci of the infiltration of the vessel walls by ApoE. We found increased number of vasa vasorum in adventitia of the small arteries. The formation and deposition of hyaline occur both from the side of the lumen of the artery and from the side of the vase vasorum. Transmission electron microscopy showed that with the development of hyalinosis, the number of smooth muscle cells that undergo atrophy. The deposition of proteins in the arterial wall is also associated with the degree of damage to endothelial cells in the lumen of the vessel and in the vasa vasorum. Conclusions These results demonstrate that, at the beginning of the development of hyalinosis, smooth muscle cells and vasa vasorum are increased. This process seem to involve oxidative stress, which damages endothelial cells both in the lumen of the arteries and in the vasorum vase and contributes to the infiltration of blood plasma proteins into the vascular wall. The resulting hyalinosis decreases the lumen of the arteries and increases the incidence of stroke. Support or Funding Information Supported by NIH

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Background The remodeling of the cerebral vascular wall contributes to the occurrence of ischemic stroke in systemic hypertension patients, representing a leading cause of death in the U.S. and worldwide. Cerebral vascular remodeling in systemic hypertension is characterized by progressive degradation of structural components of each layer of the vessel wall with the subsequent transformation to hyaline material leading to the thickening vascular wall and lumen narrowing. The vasa vasorum as a network of small blood vessels supplying the blood to the vascular wall tissues contributes to the damage vascular structure and results in the formation of hyalinosis. The occlusion of vasa vasorum contributes to development of cerebral vascular hyalinization in systemic hypertension. However, mechanisms of occlusion of vasa vasorum that contribute to the brain vascular remodeling events have not been well defined. Lack of such knowledge interferes with the development of therapeutic strategies to reduce the occurrence of ischemic stroke. Methods & Results Light microscopy and transmission electron microscopy (TEM) of hyalinized cerebral vessels from human patients who suffered from systemic hypertension and died by ischemic stroke visualized the occlusion of the vasa vasorum due to the formation of the “bulge” structure that protrude from the endothelial cells. Treatment of microvascular endothelial cell with adrenaline (a major biogenic amine that are increased in the blood due to disbalance of neurohumoral homeostasis in systemic hypertension) resulted in a cytoskeletal rearrangement that contributes to the formation of the bulge‐like structure in the vasa vasorum of the brain vessels with hyalinosis lesion. The adrenaline activated clathrin‐mediated endocytosis of endothelial cells that in turn elicited SNX9/N‐WASP‐dependent disruption of cytoskeleton. siRNA knockdown of SNX9 inhibited endocytosis and prevented the adrenaline‐induced bulge formation in human microvascular endothelial cells. TEM visualized the adrenaline‐induced an increase endocytosis of the endothelial cells. Immunofluorescence staining showed the actin filament structural reorganization and TEM confirmed myofilament damage within endothelial cells. Adrenaline treatment induced post‐translational modifications of N‐WASp as a regulator of actin polymerization. Conclusions This is the first demonstration that adrenaline contributes to the occlusion of vasa vasorum in the hyalinized cerebral vascular wall that will allow to the development new strategies that can be used to prevent ischemic stroke. Support or Funding Information Supported by NIH

Ischemic stroke is a major cause of death among patients with systemic hypertension. The narrowing of the lumen of the brain vasculature contributes to the increased incidence of stroke. While hyalinosis represents the major pathological lesions contributing to the vascular lumen narrowing and stroke, the pathogenic mechanism of brain vascular hyalinosis has not been well characterized. Thus, the present study examined the postmortem brain vasculature of human patients who died of ischemic stroke due to systemic hypertension. Hematoxylin and eosin staining and immunohistochemistry showed the occurrence of brain vascular hyalinosis with infiltrated plasma proteins along with the narrowing of vasa vasorum and oxidative stress. Transmission electron microscopy revealed the endothelial cell bulge protrusion into the vasa vasorum lumen and the occurrence of endocytosis in the vasa vasorum endothelium. The treatment of cultured microvascular endothelial cells with adrenaline also promoted the formation of the bulge as well as endocytic vesicles. siRNA knockdown of sortin nexin-9 (a mediator of clathrin-mediated endocytosis) inhibited the adrenaline-induced endothelial cell bulge formation. Adrenaline promoted protein-protein interactions between sortin nexin-9 and neural Wiskott-Aldrich Syndrome protein (a regulator of actin polymerization). We propose that endocytosis-depending endothelial cell bulge narrows the vasa vasorum, resulting in ischemic oxidative damage to the cerebral vessels, the formation of hyalinosis, the occurrence of ischemic stroke, and death in systemic hypertension patients.