Peter C. Searson

Lyme disease is a tick-borne disease primarily caused by the bacterium Borrelia burgdorferi ( Bb ). Following a tick bite, Bb is injected into the dermis and colonizes the local tissue, where it can spread to distant organs through the vascular system. Although dissemination is a crucial factor in disease progression, our understanding of the mechanisms and factors that affect Bb dissemination through circulation is incomplete. To assess the role of wall shear stress (WSS) on Bb adhesion and extravasation, we perfused a 3D tissue-engineered microvessel with fluorescently labeled Bb at different wall shear stresses. The rate of Bb adhesion and extravasation from the microvessel was strongly dependent on WSS. Bb adhered to the endothelium in an elongated morphology and occasionally exhibited “flipping” events with one end of the Bb anchored and the other end detaching and reattaching downstream. Finally, circulating Bb did not induce endothelial activation following 6 h of perfusion, although increased microvessel permeability at low WSS was correlated with increased Bb adhesion events. Our results provide a new approach to investigating Bb dissemination and offers new insights into the mechanisms of Bb extravasation. IMPORTANCE: Following a tick bite, Borrelia burgdorferi ( Bb ), the causative agent for Lyme disease, can disseminate to distant organs through the vascular system. Here, we utilize a 3D tissue-engineered microvessel model to gain insight into how wall shear stress (WSS) impacts Bb extravasation and Bb migration behavior across endothelial cells. During perfusion, Bb transiently adhered to the endothelium prior to detaching or extravasating into the surrounding extracellular matrix. The number of adhesion events was strongly dependent on WSS, and extravasation events were only observed at the lowest WSS. Adherent Bb were usually elongated and aligned in the direction of flow, and did not exhibit the helical morphology associated with migration under static conditions or in the extracellular matrix. Adherent Bb exhibited “flipping” events in which the back (upstream) end of the Bb detached and subsequently reattached downstream, becoming the front end while the other end remained anchored to the endothelium.

Smooth muscle cells (SMCs) are a critical cellular component of the tunica media of blood vessels in arteries and arterioles. Despite their importance, the development of in vitro arteriole models with diameters <200 µm remains challenging, largely due to difficulties in culturing SMCs at these length scales. In particular, uncontrolled SMC overproliferation can lead to microvessel vessel narrowing and occlusion. Here, we report a 3D microfluidic-based tissue-engineered model with human brain SMCs forming a microvessel approximately 150 μm in diameter within a collagen I hydrogel. Using this platform, we demonstrate that serum-free culture conditions are essential to prevent SMC overproliferation and maintain vessel patency. In addition, SMCs cultured in serum-free and serum-supplemented conditions exhibit distinct functional phenotypes, consistent with previous studies in 2D culture. These results provide a strategy for fabrication of tissue-engineered arteriole models.

Current assessments of brain permeability rely predominantly on drug delivery to contrast-enhancing tumor regions. However, substantial portions of central nervous system (CNS) tumors reside within non-enhancing brain (NEB), where drug concentrations frequently remain subtherapeutic. This collaborative Adult Brain Tumor Consortium and Food and Drug Administration workshop aimed to identify criteria for defining NEB permeability to accomplish two critical objectives: 1) allocate clinical trial resources toward agents achieving therapeutic NEB concentrations and 2) minimize systemic toxicity when CNS benefit is improbable. The workshop systematically evaluated permeability assessment modalities, including drug physicochemical properties, in vitro blood-brain barrier models, and penetration into cerebrospinal fluid and normal rodent brain. Methodological approaches to determine requisite NEB drug concentrations and approaches to measuring NEB pharmacokinetics and pharmacodynamics were examined. This culminated in developing the Non-Enhancing Brain Permeability Index (NEBPI), which assigns therapeutic agents to three categories: sufficiently permeable, insufficiently permeable, or impermeable. The NEBPI provides a standardized framework to assist investigators and regulatory agencies to evaluate NEB penetration before human efficacy studies are initiated for agents that require direct tumor contact. Assessing NEB drug penetration is critical to improving outcomes in CNS tumors and reducing the incidence of brain metastases in systemic malignancies.

Alzheimer’s disease is heterogeneous with a wide range of etiological subtypes derived from multiple risk factors. Many of these risk factors are eit

Blood–brain barrier (BBB) dysfunction is a hallmark of many diseases of the brain, including those that represent the largest healthcare burden (for example, Alzheimer disease and stroke). Despite this, rejuvenation and repair of the BBB is not a mainstream concept. During life, the BBB is subjected to perturbations and stresses from a wide range of endogenous or exogenous sources, which can promote brain health or can lead to brain pathologies. The BBB supports many functions that are critical for central nervous system homeostasis and so there are many mechanisms of dysfunction, and hence many targets for intervention. Furthermore, many mechanisms are shared among diseases and disease subtypes, resulting in the potential for common strategies for BBB repair. In this Review, we consider the BBB as a therapeutic target and discuss approaches to its repair and protection in specific disease states and during normal ageing.

A tissue-engineered arteriole model in a collagen I matrix with monolayers of smooth muscle cells and endothelial cells shows barrier function, pulsatile contraction/dilation, and cytokine-induced immune cell and platelet adhesion.

Lyme disease, the most widespread tick‐borne disease in North America, is caused by the bacterium Borrelia burgdorferi ( Bb ). Approximately 10–15% of infections result in neuroborreliosis, common symptoms of which include headaches, facial palsy, and long‐term cognitive impairment. Previous studies of Bb dissemination focus on assessing Bb transmigration at static time points rather than analyzing the complex dynamic process of extravasation. Furthermore, current in vitro models lack crucial physiological factors such as flow, demonstrating a need for more robust models for studying Bb dissemination to understand its dynamics and mechanisms. Here, a 3D tissue‐engineered microvessel model is used and fluorescently‐labeled Bb is perfused to model vascular dissemination in non‐tissue‐specific (iEC) and brain‐specific (iBMEC) microvessels while acquiring time‐lapse images in real time. In iECs, extravasation involves two steps: adhesion to the endothelium and transmigration into the extracellular matrix, which can be modulated through glycocalyx degradation or inflammation. In contrast, Bb extravasation in iBMECs is an extremely rare event regardless of glycocalyx degradation or inflammation. In addition, circulating Bb do not induce endothelial activation in iECs or iBMECs, but induces barrier dysfunction in iECs. These findings provide a further understanding of Bb vascular dissemination.

Blood-CNS barrier disruption is a hallmark of numerous neurological disorders, yet whether barrier breakdown is sufficient to trigger neurodegenerative disease remains unresolved. Therapeutic strategies to mitigate barrier hyperpermeability are also limited. Dominant missense mutations of the cation channel transient receptor potential vanilloid 4 (TRPV4) cause forms of hereditary motor neuron disease. To gain insights into the cellular basis of these disorders, we generated knock-in mouse models of TRPV4 channelopathy by introducing two disease-causing mutations (R269C and R232C) into the endogenous mouse Trpv4 gene. TRPV4 mutant mice exhibited weakness, early lethality, and regional motor neuron loss. Genetic deletion of the mutant Trpv4 allele from endothelial cells (but not neurons, glia, or muscle) rescued these phenotypes. Symptomatic mutant mice exhibited focal disruptions of blood–spinal cord barrier (BSCB) integrity, associated with a gain of function of mutant TRPV4 channel activity in neural vascular endothelial cells (NVECs) and alterations of NVEC tight junction structure. Systemic administration of a TRPV4-specific antagonist abrogated channel-mediated BSCB impairments and provided a marked phenotypic rescue of symptomatic mutant mice. Together, our findings show that mutant TRPV4 channels can drive motor neuron degeneration in a non–cell autonomous manner by precipitating focal breakdown of the BSCB. Further, these data highlight the reversibility of TRPV4-mediated BSCB impairments and identify a potential therapeutic strategy for patients with TRPV4 mutations.