A High-Throughput Distal Lung Air-Blood Barrier Model Enabled By Density-Driven Underside Epithelium Seeding

Nanoparticle-neutrophils interactions for autoimmune regulation

Neutrophils play an essential role as 'first responders' in the immune response, necessitating many immune-modulating capabilities. Chronic, unresolved inflammation is heavily implicated in the progression and tissue-degrading effects of autoimmune disease. Neutrophils modulate disease pathogenesis by interacting with the inflammatory and autoreactive cells through effector functions, including signaling, degranulation, and neutrophil extracellular traps (NETs) release. Since the current gold standard systemic glucocorticoid administration has many drawbacks and side effects, targeting neutrophils in autoimmunity provides a new approach to developing therapeutics. Nanoparticles enable targeting of specific cell types and controlled release of a loaded drug cargo. Thus, leveraging nanoparticle properties and interactions with neutrophils provides an exciting new direction toward novel therapies for autoimmune diseases. Additionally, recent work has utilized neutrophil properties to design novel targeted particles for delivery into previously inaccessible areas. Here, we outline nanoparticle-based strategies to modulate neutrophil activity in autoimmunity, including various nanoparticle formulations and neutrophil-derived targeting.

HIGH THROUGHPUT QUANTITATION OF HUMAN NEUTROPHIL RECRUITMENT AND FUNCTIONAL RESPONSES IN AN AIR-BLOOD BARRIER ARRAY

Dysregulated neutrophil recruitment drives many pulmonary diseases, but most preclinical screening methods are unsuited to evaluate pulmonary neutrophilia, limiting progress towards therapeutics. Namely, high throughput therapeutic screening systems typically exclude critical neutrophilic pathophysiology, including blood-to-lung recruitment, dysfunctional activation, and resulting impacts on the air-blood barrier. To meet the conflicting demands of physiological complexity and high throughput, we developed an assay of 96-well Leukocyte recruitment in an Air-Blood Barrier Array (L-ABBA-96) that enables in vivo -like neutrophil recruitment compatible with downstream phenotyping by automated flow cytometry. We modeled acute respiratory distress syndrome (ARDS) with neutrophil recruitment to 20 ng/mL epithelial-side interleukin 8 (IL-8) and found a dose dependent reduction in recruitment with physiologic doses of baricitinib, a JAK1/2 inhibitor recently FDA-approved for severe COVID-19 ARDS. Additionally, neutrophil recruitment to patient-derived cystic fibrosis sputum supernatant induced disease-mimetic recruitment and activation of healthy donor neutrophils and upregulated endothelial e-selectin. Compared to 24-well assays, the L-ABBA-96 reduces required patient sample volumes by 25 times per well and quadruples throughput per plate. Compared to microfluidic assays, the L-ABBA-96 recruits two orders of magnitude more neutrophils per well, enabling downstream flow cytometry and other standard biochemical assays. This novel pairing of high-throughput in vitro modeling of organ-level lung function with parallel high-throughput leukocyte phenotyping substantially advances opportunities for pathophysiological studies, personalized medicine, and drug testing applications.

Advances in In Vitro Blood-Air Barrier Models and the Use of Nanoparticles in COVID-19 Research

Respiratory infections caused by coronaviruses (CoVs) have become a major public health concern in the past two decades as revealed by the emergence of SARS-CoV in 2002, MERS-CoV in 2012, and SARS-CoV-2 in 2019. The most severe clinical phenotypes commonly arise from exacerbation of immune response following the infection of alveolar epithelial cells localized at the pulmonary blood-air barrier. Preclinical rodent models do not adequately represent the essential genetic properties of the barrier, thus necessitating the use of humanized transgenic models. However, existing monolayer cell culture models have so far been unable to mimic the complex lung microenvironment. In this respect, air-liquid interface models, tissue engineered models, and organ-on-a-chip systems, which aim to better imitate the infection site microenvironment and microphysiology, are being developed to replace the commonly used monolayer cell culture models, and their use is becoming more widespread every day. On the contrary, studies on the development of nanoparticles (NPs) that mimic respiratory viruses, and those NPs used in therapy are progressing rapidly. The first part of this review describes in vitro models that mimic the blood-air barrier, the tissue interface that plays a central role in COVID-19 progression. In the second part of the review, NPs mimicking the virus and/or designed to carry therapeutic agents are explained and exemplified.

Liquid plug propagation in computer-controlled microfluidic airway-on-a-chip with semi-circular microchannels

This paper introduces a two-inlet, one-outlet lung-on-a-chip device with semi-circular cross-section microchannels and computer-controlled fluidic switching that enables a broader systematic investigation of liquid plug dynamics in a manner relevant to the distal airways. A leak-proof bonding protocol for micro-milled devices facilitates channel bonding and culture of confluent primary small airway epithelial cells. Production of liquid plugs with computer-controlled inlet channel valving and just one outlet allows more stable long-term plug generation and propagation compared to previous designs. The system also captures both plug speed and length as well as pressure drop concurrently. In one demonstration, the system reproducibly generates surfactant-containing liquid plugs, a challenging process due to lower surface tension that makes the plug formation less stable. The addition of surfactant decreases the pressure required to initiate plug propagation, a potentially significant effect in diseases where surfactant in the airways is absent or dysfunctional. Next, the device recapitulates the effect of increasing fluid viscosity, a challenging analysis due to higher resistance of viscous fluids that makes plug formation and propagation more difficult particularly in airway-relevant length scales. Experimental results show that increased fluid viscosity decreases plug propagation speed for a given air flow rate. These findings are supplemented by computational modeling of viscous plug propagation that demonstrates increased plug propagation time, increased maximum wall shear stress, and greater pressure differentials in more viscous conditions of plug propagation. These results match physiology as mucus viscosity is increased in various obstructive lung diseases where it is known that respiratory mechanics can be compromised due to mucus plugging of the distal airways. Finally, experiments evaluate the effect of channel geometry on primary human small airway epithelial cell injury in this lung-on-a-chip. There is more injury in the middle of the channel relative to the edges highlighting the role of channel shape, a physiologically relevant parameter as airway cross-sectional geometry can also be non-circular. In sum, this paper describes a system that pushes the device limits with regards to the types of liquid plugs that can be stably generated for studies of distal airway fluid mechanical injury.

Liquid plug propagation in computer-controlled microfluidic airway-on-a-chip with semi-circular microchannels

This paper introduces a two-inlet, one-outlet lung-on-a-chip device with semi-circular cross-section microchannels and computer-controlled fluidic switching that enables a broader systematic investigation of liquid plug dynamics in a manner relevant to the distal airways. A leak-proof bonding protocol for micro-milled devices facilitates channel bonding and culture of confluent primary small airway epithelial cells. Production of liquid plugs with computer-controlled inlet channel valving and just one outlet allows more stable long-term plug generation and propagation compared to previous designs. The system also captures both plug speed and length as well as pressure drop concurrently. In one demonstration, the system reproducibly generates surfactant-containing liquid plugs, a challenging process due to lower surface tension that makes the plug formation less stable. The addition of surfactant decreases the pressure required to initiate plug propagation, a potentially significant effect in diseases where surfactant in the airways is absent or dysfunctional. Next, the device recapitulates the effect of increasing fluid viscosity, a challenging analysis due to higher resistance of viscous fluids that makes plug formation and propagation more difficult particularly in airway-relevant length scales. Experimental results show that increased fluid viscosity decreases plug propagation speed for a given air flow rate. These findings are supplemented by computational modeling of viscous plug propagation that demonstrate increased plug propagation time, increased maximum wall shear stress, and greater pressure differentials in more viscous conditions of plug propagation. These results match physiology as mucus viscosity is increased in various obstructive lung diseases where it is known that respiratory mechanics can be compromised due to mucus plugging of the distal airways. Finally, experiments evaluate the effect of channel geometry on primary human small airway epithelial cell injury in this lung-on-a-chip. There is more injury in the middle of the channel relative to the edges highlighting the role of channel shape, a physiologically relevant parameter as airway cross-sectional geometry can also be non-circular. In sum, this paper describes a system that pushes the device limits with regards to the types of liquid plugs that can be stably generated for studies of distal airway fluid mechanical injury.

Injured Endothelial Cell: A Risk Factor for Pulmonary Fibrosis

The pathological features of pulmonary fibrosis (PF) are the abnormal activation and proliferation of myofibroblasts and the extraordinary deposition of the extracellular matrix (ECM). However, the pathogenesis of PF is still indistinct. In recent years, many researchers have realized that endothelial cells had a crucial role in the development of PF. Studies have demonstrated that about 16% of the fibroblasts in the lung tissue of fibrotic mice were derived from endothelial cells. Endothelial cells transdifferentiated into mesenchymal cells via the endothelial-mesenchymal transition (E(nd)MT), leading to the excessive proliferation of endothelial-derived mesenchymal cells and the accumulation of fibroblasts and ECM. This suggested that endothelial cells, a significant component of the vascular barrier, played an essential role in PF. Herein, this review discusses E(nd)MT and its contribution to the activation of other cells in PF, which could provide new ideas for further understanding the source and activation mechanism of fibroblasts and the pathogenesis of PF.

Generation of Alveolar Epithelium Using Reconstituted Basement Membrane and hiPSC-Derived Organoids

In vitro modeling of alveolar epithelium needs to recapitulate features of both cellular and noncellular components of the lung tissues. Herein, a method is presented to generate alveolar epithelium by using human induced pluripotent stem cells (hiPSCs) and reconstituted or artificial basement membrane (ABM). The ABM is obtained by self-assembling type IV collagen and laminin with a monolayer of crosslinked gelatin nanofibers as backbone and a patterned honeycomb microframe for handling. Alveolar organoids are obtained from hiPSCs and then dissociated into single cells. After replating the alveolar cells on the ABM and a short-period incubation under submerged and air-liquid interface culture conditions, an alveolar epithelium is achieved, showing high-level expressions of both alveolar cell-specific proteins and characteristic tight junctions. Besides, endothelial cells derived from the same hiPSCs are cocultured on the backside of the epithelium, forming an air-blood barrier. The method is generic and can potentially be applied to other types of artificial epithelium and endothelium.