Cardiovascular pathologies such as intracranial aneurysms (IAs) and atherosclerosis preferentially localize to bifurcations and curvatures where hemodynamics are complex. While extensive knowledge about low wall shear stress (WSS) has been generated in the past, due to its strong relevance to atherogenesis, high WSS (typically >3 Pa) has emerged as a key regulator of vascular biology and pathology as well, receiving renewed interests. As reviewed here, chronic high WSS not only stimulates adaptive outward remodeling, but also contributes to saccular IA formation (at bifurcation apices or outer curves) and atherosclerotic plaque destabilization (in stenosed vessels). Recent advances in understanding IA pathogenesis have shed new light on the role of high WSS in pathological vascular remodeling. In complex geometries, high WSS can couple with significant spatial WSS gradient (WSSG). A combination of high WSS and positive WSSG has been shown to trigger aneurysm initiation. Since endothelial cells (ECs) are sensors of WSS, we have begun to elucidate EC responses to high WSS alone and in combination with WSSG. Understanding such responses will provide insight into not only aneurysm formation, but also plaque destabilization and other vascular pathologies and potentially lead to improved strategies for disease management and novel targets for pharmacological intervention.

Cerebral aneurysms develop near bifurcation apices, where complex hemodynamics occur: Flow impinges on the apex, accelerates into branches, then slows again distally, creating high wall shear stress (WSS) and positive and negative spatial gradients in WSS (WSSG). Endothelial responses to these kinds of high WSS hemodynamic environments are not well characterized. We examined endothelial cells (ECs) under elevated WSS and positive and negative WSSG using a flow chamber with constant-height channels to create regions of uniform WSS and converging and diverging channels to create positive and negative WSSG, respectively. Cultured bovine aortic ECs were subjected to 3.5 and 28.4 Pa with and without WSSG for 24 and 36 h. High WSS inhibited EC alignment to flow, increased EC proliferation assessed by bromodeoxyuridine incorporation, and increased apoptosis determined by terminal deoxynu-cleotidyl transferase dUTP-mediated nick-end labeling. These responses to high WSS were either accentuated or ameliorated by WSSG: Positive WSSG (+980 Pa/m) inhibited alignment and stimulated proliferation and apoptosis, whereas negative WSSG (−1120 Pa/m) promoted alignment and suppressed proliferation and apoptosis. These results demonstrate that ECs discriminate between positive and negative WSSG under high WSS conditions. EC responses to positive WSSG may contribute to pathogenic remodeling that occurs at bifurcations preceding aneurysm formation.

Chronic high flow can induce arterial remodeling, and this effect is mediated by endothelial cells (ECs) responding to wall shear stress (WSS). To assess how WSS above physiological normal levels affects ECs, we used DNA microarrays to profile EC gene expression under various flow conditions. Cultured bovine aortic ECs were exposed to no-flow (0 Pa), normal WSS (2 Pa), and very high WSS (10 Pa) for 24 h. Very high WSS induced a distinct expression profile compared with both no-flow and normal WSS. Gene ontology and biological pathway analysis revealed that high WSS modulated gene expression in ways that promote an anti-coagulant, anti-inflammatory, proliferative, and promatrix remodeling phenotype. A subset of characteristic genes was validated using quantitative polymerase chain reaction: very high WSS upregulated ADAMTS1 (a disintegrin and metalloproteinase with thrombospondin motif-1), PLAU (urokinase plasminogen activator), PLAT (tissue plasminogen activator), and TIMP3, all of which are involved in extracellular matrix processing, with PLAT and PLAU also contributing to fibrinolysis. Downregulated genes included CXCL5 and IL-8 and the adhesive glycoprotein THBS1 (thrombospondin-1). Expressions of ADAMTS1 and uPA proteins were assessed by immunhistochemistry in rabbit basilar arteries experiencing increased flow after bilateral carotid artery ligation. Both proteins were significantly increased when WSS was elevated compared with sham control animals. Our results indicate that very high WSS elicits a unique transcriptional profile in ECs that favors particular cell functions and pathways that are important in vessel homeostasis under increased flow. In addition, we identify specific molecular targets that are likely to contribute to adaptive remodeling under elevated flow conditions.

Current randomized trials and observational studies evaluating higher versus lower protein doses in critically ill patients yield inconclusive results. Because of few studies and methodologic limitations, clinical guidelines suggest a wide range of protein intake based on weak evidence. Clinical equipoise about protein dosing exists. The purpose of the current manuscript is to provide the rationale and protocol for a randomized controlled trial (RCT) of 4000 critically ill patients randomly allocated to receive a higher or lower protein dose. We propose a global, volunteer‐driven, registry‐based RCT involving >100 intensive care units (ICUs). We will enroll mechanically ventilated patients with high nutrition risk, identified by low (≤25) or high (≥35) body mass index, moderate to severe malnutrition, frailty, sarcopenia, or when >96‐hour duration of mechanical ventilation is expected. Exclusion criteria include patients who are >96 hours since initiation of mechanical ventilation, moribund, or pregnant, and where the clinician lacks clinical equipoise regarding protein dose. The intervention consists of higher (≥2.2 g/kg/d) or lower (≤1.2 g/kg/d) protein dose, achieved by enteral nutrition, parenteral nutrition, or both. The primary outcome will be 60‐day mortality. Key secondary outcomes include time‐to‐discharge alive from hospital, ICU and hospital survival, and length of stay. As this is research based on existing medical practice, we will apply for a waiver of informed consent, where possible. The large sample size is a reflection of the small signal we expect to see in this large, pragmatic trial.

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, and flow acceleration and deceleration in the branches create positive and negative streamwise gradients in WSS (WSSG), respectively. Intracranial aneurysms tend to form in regions with high WSS and positive WSSG. However, little is known about the responses of endothelial cells (ECs) to either positive or negative WSSG under high WSS conditions. We used cDNA microarrays to profile gene expression in cultured ECs exposed to positive or negative WSSG for 24 h in a flow chamber where WSS varied between 3.5 and 28.4 Pa. Gene ontology and biological pathway analysis indicated that positive WSSG favored proliferation, apoptosis, and extracellular matrix processing while decreasing expression of proinflammatory genes. To determine if similar responses occur in vivo, we examined EC proliferation and expression of the matrix metalloproteinase ADAMTS1 under high WSS and WSSG created at the basilar terminus of rabbits after bilateral carotid ligation. Precise hemodynamic conditions were determined by computational fluid dynamic simulations from three-dimensional angiography and mapped on immunofluorescence staining for the proliferation marker Ki-67 and ADAMTS1. Both proliferation and ADAMTS1 were significantly higher in ECs under positive WSSG than in adjacent regions of negative WSSG. Our results indicate that WSSG elicits distinct EC gene expression profiles and particular biological pathways including increased cell proliferation and matrix processing. Such EC responses may be important in understanding the mechanisms of intracranial aneurysm initiation at regions of high WSS and positive WSSG. high wall shear stress; microarray; intracranial aneurysm initiation; vascular remodeling; spatial gradient AS THE INNERMOST LINING OF the blood vessel wall, endothelial cells (ECs) are the signal transduction interface between wall shear stress (WSS) exerted on the lining by flowing blood and the responses of underlying tissue. It is well known that endothelial structure, function, and gene expression are modulated by normal WSS (1.5-2.5 Pa) and that ECs respond differently when exposed to relatively low WSS (Ͻ0.4 Pa), and this effect is believed to play a role in atherosclerosis (21). However, endothelial responses under considerably higher WSS (Ͼ10 Pa) are not well characterized. Such high WSS occurs in arteries feeding arteriovenous fistulas (37, 42), in stenosed vessels (33, 34), in collateral arteries secondary to blockage (36, 50), and at arterial bifurcations, where high WSS predisposes intracranial vessels to aneurysm formation (24, 26).There is mounting evidence that ECs are also sensitive to spatial differences in WSS over their luminal surface, specifically to streamwise gradients in WSS [WSS gradient (WSSG)]. The effects of WSSG under low WSS have been examined in vitro in flow recirculation zones, which in vivo are prone to atherogenesis (10, 56). Under low WSS and WSSG, ECs show increased permeability (31), migration (5, 46), proliferation (46), and activation of the transcription factors NF-B, Egr-1, c-Jun, an...

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