Calcium Load in the Aortic Valve, Aortic Root, and Left Ventricular Outflow Tract and the Risk for a Periprocedural Stroke.

Background: Periprocedural stroke during transcatheter aortic valve implantation is a rare but devastating complication. The calcified aortic valve is the most likely source of the emboli in a periprocedural stroke. The total load and distribution of calcium in the leaflets, aortic root, and left ventricular outflow tract varies from patient to patient. Consequently, there could be patterns of calcification that are associated with a higher risk of stroke. This study aimed to explore whether the pattern of calcification in the left ventricular outflow tract, annulus, aortic valve, and ascending aorta can be used to predict a periprocedural stroke. Methods: Among the 3282 consecutive patients who received a transcatheter aortic valve implantation in the native valve in Sweden from 2014 to 2018, we identified 52 who had a periprocedural stroke. From the same cohort, a control group of 52 patients was constructed by propensity score matching. Both groups had one missing cardiac computed tomography, and 51 stroke and 51 control patients were blindly reviewed by an experienced radiologist. Results: The groups were well balanced in terms of demographics and procedural data. Of the 39 metrics created to describe calcium pattern, only one differed between the groups. The length of calcium protruding above the annulus was 10.6 mm (interquartile range 7-13.6) for patients without stroke and 8 mm (interquartile range 3-10) for stroke patients. Conclusions: This study could not find any pattern of calcification that predisposes for a periprocedural stroke.

Functional and structural adaptations of coronary microvessels distal to a chronic coronary artery stenosis.

Distal to a chronic coronary artery stenosis, structural remodeling of the microvasculature occurs. The microvascular functional changes distal to the stenosis have not been studied in detail. We tested the hypothesis that microvascular structural remodeling is accompanied by altered regulation of coronary vasomotor tone with increased responsiveness to endothelin-1. Vasomotor tone was studied in coronary microvessels from healthy control swine and from swine 3 to 4 months after implantation of an occluder that causes a progressive coronary narrowing, resulting in regional left ventricular dysfunction and blunted myocardial vasodilator reserve. Arterioles (approximately 200-microm passive inner diameter at 60 mm Hg) were isolated from regions perfused by the stenotic left anterior descending and normal left circumflex coronary arteries and studied in vitro. Passive pressure-diameter curves demonstrated reduced distensibility of subendocardial left anterior descending compared with subendocardial left circumflex or control arterioles, suggestive of structural remodeling. Myogenic responses were blunted in subendocardial left anterior descending compared with left circumflex arterioles, reflecting altered smooth muscle function. However, vasodilator responses to nitroprusside and bradykinin were not different in the endocardium, suggesting preserved endothelium and smooth muscle responsiveness. Finally, vasoconstrictor responses to endothelin-1 were enhanced in left anterior descending arterioles compared with left circumflex or control arterioles. Regional myocardial vascular conductance responses to bradykinin and endothelin in vivo confirmed the in vitro observations. In conclusion, inward remodeling of coronary microvessels distal to a stenosis is accompanied by exaggerated vasoconstrictor responses to endothelin-1. These structural and functional alterations may aggravate flow abnormalities distal to a chronic coronary artery stenosis.

Transglutaminases in vascular biology: relevance for vascular remodeling and atherosclerosis.

The transglutaminase (Tgase) family consists of nine known members of whom at least three are expressed in the vascular system: type 1 Tgase, type 2 Tgase and factor XIII. The cross-linking of proteins is a characteristic feature of Tgases, of well-known importance for stabilizing the blood clot and providing mechanical strength to tissues. However, recent data suggest that Tgases play a role in several other processes in vascular biology. These newly discovered areas include endothelial barrier function, small artery remodeling, and atherosclerosis.

Small artery remodeling and erythrocyte deformability in L-NAME-induced hypertension: role of transglutaminases.

BACKGROUND: Hypertension is associated with inward remodeling of small arteries and decreased erythrocyte deformability, both impairing proper tissue perfusion. We hypothesized that these alterations depend on transglutaminases, cross-linking enzymes present in the vascular wall, monocytes/macrophages and erythrocytes. METHODS AND RESULTS: Wild-type (WT) mice and tissue-type transglutaminase (tTG) knockout (KO) mice received the nitric oxide inhibitor Nomega-nitro-L-arginine methyl ester hydrochloride (L-NAME) to induce hypertension. After 1 week, mesenteric arteries from hypertensive WT mice showed a smaller lumen diameter (-6.9 +/- 2.0%, p = 0.024) and a larger wall-to-lumen ratio (11.8 +/- 3.5%, p = 0.012) than controls, whereas inward remodeling was absent in hypertensive tTG KO mice. After 3 weeks, the wall-to-lumen ratio was increased in WT (20.8 +/- 4.8%, p = 0.005) but less so in tTG KO mice (11.7 +/- 4.6%, p = 0.026), and wall stress was normalized in WT but not in tTG KO mice. L-NAME did not influence expression of tTG or an alternative transglutaminase, coagulation factor XIII (FXIII). Suppression of FXIII by macrophage depletion was associated with increased tTG in the presence of L-NAME. L-NAME treatment decreased erythrocyte deformability in the WT mice (-15.3% at 30 dynes/cm(2), p = 0.014) but not in the tTG KO mice. CONCLUSION: Transglutaminases are involved in small artery inward remodeling and erythrocyte stiffening associated with nitric oxide inhibition-related hypertension.

Flow-dependent remodeling of small arteries in mice deficient for tissue-type transglutaminase: possible compensation by macrophage-derived factor XIII.

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.

Decomposition cross-correlation for analysis of collagen matrix deformation by single smooth muscle cells.

Microvascular remodeling is known to depend on cellular interactions with matrix tissue. However, it is difficult to study the role of specific cells or matrix elements in an in vivo setting. The aim of this study is to develop an automated technique that can be employed to obtain and analyze local collagen matrix remodeling by single smooth muscle cells. We combined a motorized microscopic setup and time-lapse video microscopy with a new cross-correlation based image analysis algorithm to enable automated recording of cell-induced matrix reorganization. This method rendered 60-90 single cell studies per experiment, for which collagen deformation over time could be automatically derived. Thus, the current setup offers a tool to systematically study different components active in matrix remodeling.

Mechanics of microvascular remodeling.

This paper reviews work on microvascular remodeling that has been done over the past years in our lab. It is not our purpose to fully cover the field; rather we explain our progress in a more or less chronological order. We address physiological and pathological remodeling in resistance vessels, the biomechanics of the vascular wall and the factors that determine vascular caliber. Subsequently, the intimate link between maintained vascular tone and inward remodeling is discussed, and we highlight our view that tone and remodeling form hallmarks in a continuous process of vascular adaptation. Finally, the role of transglutaminases in remodeling is described.

Vascular smooth muscle cells remodel collagen matrices by long-distance action and anisotropic interaction.

While matrix remodeling plays a key role in vascular physiology and pathology, the underlying mechanisms have remained incompletely understood. We studied the remodeling of collagen matrices by individual vascular smooth muscle cells (SMCs), clusters and monolayers. In addition, we focused on the contribution of transglutaminase 2 (TG2), which plays an important role in the remodeling of small arteries. Single SMCs displaced fibers in collagen matrices at distances up to at least 300 µm in the course of 8-12 h. This process involved both 'hauling up' of matrix by the cells and local matrix compaction at a distance from the cells, up to 200 µm. This exceeded the distance over which cellular protrusions were active, implicating the involvement of secreted enzymes such as TG2. SMC isolated from TG2 KO mice still showed compaction, with changed dynamics and relaxation. The TG active site inhibitor L682777 blocked local compaction by wild type cells, strongly reducing the displacement of matrix towards the cells. At increasing cell density, cells cooperated to establish compaction. In a ring-shaped collagen matrix, this resulted in preferential displacement in the radial direction, perpendicular to the cellular long axis. This process was unaffected by inhibition of TG2 cross-linking. These results show that SMCs are capable of matrix remodeling by prolonged, gradual compaction along their short axis. This process could add to the 3D organization and remodeling of blood vessels based on the orientation and contraction of SMCs.

Calcium channel blockade prevents pressure-dependent inward remodeling in isolated subendocardial resistance vessels.

The capacity for myocardial perfusion depends on the structure of the coronary microvascular bed. Coronary microvessels may adapt their structure to various stimuli. We tested whether the local pressure profile affects tone and remodeling of porcine coronary microvessels. Subendocardial vessels (approximately 160 microm, n=53) were cannulated and kept in organoid culture for 3 days under different transvascular pressure profiles: Osc 80: mean 80 mmHg, 60 mmHg peak-peak sine wave pulsation amplitude at 1.5 Hz; St 80: steady 80 mmHg; Osc 40: mean 40 mmHg, 30 mmHg amplitude; St 40: steady 40 mmHg. Under the Osc 80 profile, modest tone developed, reducing the diameter to 81+/-14% (mean+/-SE, n=6) of the maximal, passive diameter. No inward remodeling was found here, as determined from the passive pressure-diameter relation after 3 days of culture. Under all other profiles, much more tone developed (e.g., Osc 40: to 26+/-3%, n=7). In addition, these vessels showed eutrophic (i.e., without a change in wall cross-sectional area) inward remodeling (e.g., Osc 40: passive diameter reduction by 24+/-3%). The calcium blocker amlodipine induced maintained dilation in St 40 vessels and reversed the 22+/-3% (n=6) inward remodeling to 15+/-3% (n=8) outward remodeling toward day 3. Vessels required a functional endothelium to maintain structural integrity in culture. Our data indicate that reduction of either mean pressure or pulse pressure leads to microvascular constriction followed by inward remodeling. These effects could be reversed by amlodipine. Although microvascular pressure profiles distal to stenoses are poorly defined, these data suggest that vasodilator therapy could improve subendocardial microvascular function and structure in coronary artery disease.

Flow inhibits inward remodeling in cannulated porcine small coronary arteries.

The mechanisms of flow-induced vascular remodeling are poorly understood, especially in the coronary microcirculation. We hypothesized that application of flow in small coronary arteries in organoid culture would cause a nitric oxide (NO)-mediated dilation and inhibit inward remodeling. We developed an organoid culture setup to drive a flow through cannulated arterioles at constant luminal pressure via a pressure gradient between the pipettes. Subepicardial porcine coronary arterioles with diameter at full dilation and 60 mmHg (D0) of 168 +/- 10 (SE) microm were cannulated. Vessels treated with Nomega-nitro-L-arginine (L-NNA) to block NO production and untreated vessels were pressurized at 60 mmHg for 3 days with and without flow. Endothelium-dependent dilation to 10(-7) M bradykinin was preserved in all groups. Tone was significantly less in vessels cultured under flow conditions in the last half of the culture period. Untreated and L-NNA-treated vessels regulated their diameter to yield shear stresses of 10.3 +/- 2.1 and 14.0 +/- 2.4 (SE) dyn/cm2, respectively (not significantly different). Without L-NNA, passive pressure-diameter curves at the end of the culture period revealed inward remodeling in the control group [to 92.3 +/- 1.3% of D0 (SE)] and no remodeling in the vessels cultured under flow conditions (100.2 +/- 1.3% of D0); with L-NNA, the group subjected to flow showed inward remodeling (92.1 +/- 2.5% of D0). We conclude that pressurized coronary resistance arteries could be maintained in culture for several days with flow. Vessels cultured under flow conditions remained more dilated when NO synthesis was blocked. Inward remodeling occurred in vessels cultured under no-flow conditions and was inhibited by flow-dependent NO synthesis.