Flow-Dependent Remodeling of Small Arteries in Mice Deficient for Tissue-Type Transglutaminase

Chronic changes in blood flow induce an adaptation of vascular caliber. Thus, arteries show inward remodeling after a reduction in blood flow. We hypothesized that this remodeling depends on the crosslinking enzyme tissue-type transglutaminase (tTG). Flow-dependent remodeling was studied in wild-type (WT) and tTG-null mice using a surgically imposed change in blood flow in small mesenteric arteries. WT mice showed inward remodeling after 2 days of low blood flow, which was absent in arteries from tTG-null mice. Yet, after continued low blood flow for 7 days, inward remodeling was similar in arteries from WT and tTG-null mice. Studying the alternative pathways of remodeling, we identified a relatively high expression of the plasma transglutaminase factor XIII in arteries of WT and tTG-null mice. In addition, vessels from both WT and tTG-null mice showed the presence of transglutaminase-specific crosslinks. An accumulation of adventitial monocytes/macrophages was found in vessels exposed to low blood flow in tTG-null mice. Because monocytes/macrophages may represent a source of factor XIII, tTG-null mice were treated with liposome-encapsulated clodronate. Elimination of monocytes/macrophages with liposome-encapsulated clodronate reduced both the expression of factor XIII and inward remodeling in tTG-null mice. In conclusion, tTG plays an important role in the inward remodeling of small arteries associated with decreased blood flow. Adventitial monocytes/macrophages are a source of factor XIII in tTG-null mice and contribute to an alternative, delayed mechanism of inward remodeling when tTG is absent

Lymphatic clearance of the brain: perivascular, paravascular and significance for neurodegenerative diseases

The lymphatic clearance pathways of the brain are different compared to the other organs of the body and have been the subject of heated debates. Drainage of brain extracellular fluids, particularly interstitial fluid (ISF) and cerebrospinal fluid (CSF), is not only important for volume regulation, but also for removal of waste products such as amyloid beta (A?). CSF plays a special role in clinical medicine, as it is available for analysis of biomarkers for Alzheimer’s disease. Despite the lack of a complete anatomical and physiological picture of the communications between the subarachnoid space (SAS) and the brain parenchyma, it is often assumed that A? is cleared from the cerebral ISF into the CSF. Recent work suggests that clearance of the brain mainly occurs during sleep, with a specific role for peri- and para-vascular spaces as drainage pathways from the brain parenchyma. However, the direction of flow, the anatomical structures involved and the driving forces remain elusive, with partially conflicting data in literature. The presence of A? in the glia limitans in Alzheimer’s disease suggests a direct communication of ISF with CSF. Nonetheless, there is also the well-described pathology of cerebral amyloid angiopathy associated with the failure of perivascular drainage of A?. Herein, we review the role of the vasculature and the impact of vascular pathology on the peri- and para-vascular clearance pathways of the brain. The different views on the possible routes for ISF drainage of the brain are discussed in the context of pathological significance

Extravasation of biodegradable microspheres in the rat brain

AbstractDrug development for neurological diseases is greatly impeded by the presence of the blood-brain barrier (BBB). We and others previously reported on extravasation of micrometer-sized particles from the cerebral microcirculation – across the BBB – into the brain tissue over the course of several weeks. This mechanism could potentially be used for sustained parenchymal drug delivery after extravasation of biodegradable microspheres. As a first step toward this goal, we set out to evaluate the extravasation potential in the rat brain of three classes of biodegradable microspheres with drug-carrying potential, having a median diameter of 13 µm (80% within 8–18 µm) and polyethylene glycol concentrations of 0%, 24% and 36%. Extravasation, capillary recanalization and tissue damage were determined in a rat cerebral microembolization model at day 14 after microsphere injection. Microspheres of all three classes had the potential to extravasate from the vessel into the brain parenchyma, with microspheres without polyethylene glycol extravasating the fastest. Microembolization with biodegradable microspheres led to impaired local capillary perfusion, which was substantially restored after bead extravasation. We did not observe overt tissue damage after microembolization with any microsphere: we found very limited BBB disruption (IgG extravasation), no microgliosis (Iba1 staining) and no large neuronal infarctions (NeuN staining). In conclusion, biodegradable microspheres with different polymer compositions can extravasate into the brain parenchyma while causing minimal tissue damage

Calcification Locates to Transglutaminases in Advanced Human Atherosclerotic Lesions

Transglutaminases play an important role in vascular smooth muscle cell-induced calcification in vitro. In this study, we determined whether these enzymes are also involved in human atherosclerotic calcification using nine carotid artery specimens obtained at endarterectomy. Sections of the carotid artery specimens were registered to micro-computed tomography images and stained for tissue-type transglutaminase, plasma transglutaminase factor XIIIA (FXIIIA), the Nε(γ-glutamyl)lysine cross-link, and the macrophage marker CD68. Ex vivo micro-computed tomography revealed extensive calcification, which significantly correlated with the cross-link. FXIIIA was found to be the dominant transglutaminase, rather than tissue-type transglutaminase, although staining of both transglutaminases correlated with the cross-link. Staining for FXIIIA colocalized with CD68 at both the cellular and tissue level. In conclusion, areas of calcification locate to the presence and activity of transglutaminases in human atherosclerotic arteries. FXIIIA seems to be the dominant transglutaminase and may be derived from local macrophages. These results are consistent with the hypothesis that transglutaminases participate in the calcification process of human atherosclerotic arteries

TR3 Nuclear Orphan Receptor Prevents Cyclic Stretch-Induced Proliferation of Venous Smooth Muscle Cells

In coronary artery bypass surgery, the patency of arterial grafts is higher than that of venous grafts because of vein-graft disease, which involves excessive proliferation of venous smooth muscle cells (SMCs) and subsequent accelerated atherosclerosis. We studied the function of TR3 nuclear orphan receptor (TR3) in the early response of SMCs to mechanical strain, a major initiator of vein-graft disease. We demonstrate that TR3 expression is induced in human saphenous vein segments exposed ex vivo to whole-blood perfusion under arterial pressure. Cultured venous SMCs challenged by cyclic stretch displayed TR3 induction and enhanced DNA synthesis, whereas SMCs derived from the internal mammary artery remained quiescent. Small-interfering RNA-mediated knockdown of TR3 and adenovirus-mediated overexpression of TR3 in venous SMCs enhanced and abolished stretch-induced DNA synthesis, respectively. Accordingly, in organ cultures of wild-type murine vessel segments exposed to cyclic stretch, p27(Kip1) was down-regulated, whereas expression of this cell cycle inhibitor was unaffected by cyclic stretch in TR3-transgenic vessels, concordant with a lower proliferative response. Finally, stretch-mediated proliferation was inhibited by 6-mercaptopurine, an agonist of TR3. In conclusion, TR3 represents inhibitory mechanisms to restrict venous SMC proliferation and may contribute to prevention of vein-graft disease