Martin Conrad Harmsen

Modeling immune cell recruitment within a wound-relevant microenvironment remains challenging. Here, we developed a novel skin-derived extracellular matrix (ECM) hydrogel model to study monocyte (THP-1) entry and phenotypic changes within a dermal fibroblast-populated (NHDF) matrix. The main novelty of this study is that it compares the effects of fibroblast-derived soluble signals and active monocyte infiltration in a 3D biomimetic model. Signaling by fibroblast-secreted soluble factors enhanced a pro-angiogenic secretome (e.g., >3-fold upregulation of VEGFA at day 1) and promoted endothelial tube formation (increasing network junctions to 1.16 ± 0.16 vs. 0.93 ± 0.23 in monoculture). In contrast, this paracrine signaling did not induce the matrix-driven pro-fibrotic response in hydrogels. Crucially, physical immune infiltration restricted monocyte penetration (mean depth of 8.92 ± 2.27 μm vs. 121.1 ± 15.9 μm in monoculture at day 5), reduced hydrogel-induced myofibroblast activation (decreasing α-SMA+ cells from 79.1% to 54.3% upon initial contact), and was associated with slower collagen loss during the early phase. (retaining a high-density collagen ratio of 3.46 ± 0.33 vs. 2.02 ± 0.29 in monoculture at day 1). These observations were accompanied by a shift toward a matrix-stabilizing profile, including increased TIMP expression and reduced pro-fibrotic markers. (ACTA2 and COL1A1). By including active immune infiltration (which was absent in previous tSVF models), we capture the transition from inflammation to the proliferation stage. Although the later stages of extensive ECM remodeling appear suppressed here, they may occur as repair progresses. Overall, our findings highlight that the immune cell is a key regulatory component for coordinating matrix preservation and vascular support. Importantly, this model replicates the early phases of wound healing, a stage where the monocyte–fibroblast secretome supports endothelial network formation. We established this innovative 3D ECM hydrogel system as a practical and physiologically relevant platform to investigate immune–matrix–stromal crosstalk.

Transitions in mechanical properties between different tissue scaffolds, such as extracellular matrices (ECMs), are common in the human body and influence cellular orientation. For example, in teeth, the abrupt transition between soft (approx5 kPa) dental pulp and stiff (more than100 kPa) dentin directs the alignment of odontoblasts. In this study, hydrogels, with defined mechanical transitions were used to evaluate the phenotypic response of fibroblasts to either a soft/soft (3 kPa/3 kPa) or soft/stiff (3 kPa/200 kPa) interface. Near the soft/soft interface fibroblasts aligned in a more parallel fashion to the interface (11 degree angle to the interface), compared to the more perpendicular fashion (69 degree angle to the interface) observed at the soft-stiff interface. Notably, regions of alignment also showed an increased proportion of alpha smooth muscle actin (alpha-SMA)-positive cells, indicating myofibroblast differentiation in response to the mechanical transition. These findings demonstrate that modifying a biomaterial by introducing an interface alters the bioactivity of responding cells solely through mechanical mechanisms, without any change to the cells biochemical environment.

Chronic obstructive pulmonary disease (COPD) is characterized by progressive airflow limitation and emphysema development, associated with enhanced tissue destruction and defective repair. Supporting cells in the alveolar niche play a crucial role in guiding the activation of alveolar epithelial progenitor cells during repair. Despite their close anatomical proximity, understanding of the supportive role of the pulmonary microvascular endothelium in adult alveolar epithelial repair remains limited. We hypothesized that factors secreted by pulmonary endothelial cells support alveolar epithelial cell growth. Here, we report that human pulmonary microvasculature endothelial cells support murine and human alveolar organoid formation through paracrine signaling via the secretion of extracellular vesicles and soluble factors. Transcriptomic and proteomic analysis pinpointed human pulmonary microvasculature endothelial cell–derived BMP6 (bone morphogenetic protein 6) as a critical factor for alveolar organoid formation. BMP6 promoted alveolar epithelial cell growth, whereas function-blocking antibodies targeting BMP6 inhibited the beneficial effect of endothelial cells on murine alveolar organoid formation. Transcriptomic analysis revealed that BMP6 specifically enhances distal epithelial cell markers and increases Wnt signaling in epithelial progenitors. In contrast, BMP6 deficiency in mouse lungs was associated with reduced Wnt signaling and augmented oxidative stress signaling in murine lung tissue. Taken together, our findings highlight BMP6 as a key regulator of adult epithelial repair and suggest its potential as a therapeutic target for defective epithelial repair, particularly in individuals with early stages of COPD.

The alveolus is central to gas exchange in the lung, and alveolar damage is a characteristics of a variety of lung diseases. Understanding alveolar microvascular dynamics and epithelial-endothelial interactions is essential for accurately modeling alveolar physiology and its dysfunction in lung diseases such as Chronic Obstructive Pulmonary Disease (COPD), pulmonary fibrosis and acute respiratory distress syndrome (ARDS). In this study, we present an open-top, membrane-free alveolus-on-chip platform incorporating self-assembled, perfusable 3D vascular networks by primary human lung endothelial cells and pericytes, co-cultured with alveolar epithelial type 2 (AEC2) cells. These vascular networks were developed within 6 days under continuous flow and remained stable for at least 12 days. The inclusion of pericytes supported capillary-like vessel formation and increased gene expression of EDNRB1 , a gene enriched in alveolar microvascular endothelial cells. Furthermore, CD31 gene expression was higher in 3D endothelial networks compared to 2D endothelial monolayers, suggesting increased cell-cell adhesion. Monocytes could be successfully perfused through the networks, expanding the platform’s potential for studying immune interactions in lung disorders. Culturing AEC2 monolayers directly on the vascularized hydrogel enabled physiologically relevant cell-cell interactions without artificial membranes, while maintaining air-liquid interface conditions. Importantly, exposure of the AEC2 layer to whole cigarette smoke (WCS) led to complete disintegration of the underlying vascular network, an effect not observed in the absence of AEC2. This chip model provides a human-relevant system for investigating vascular-epithelial crosstalk in the alveolus, smoke-induced lung injury, and immune recruitment, offering a valuable platform for future disease modeling and drug testing applications.

Pulmonary arterial hypertension (PAH) is a rare, progressive, and incurable disease characterized by an elevated pulmonary blood pressure, extensive remodeling of the pulmonary vasculature, increased pulmonary vascular resistance, and culminating in right ventricular failure. Mitochondrial dysfunction has a major role in the pathogenesis of PAH and secondary right ventricular failure, and its targeting may offer therapeutic benefit. In this study, we provide proof-of-concept for the use of the mitochondrially active drug SUL-150 to treat PAH. PAH was induced in rats by monocrotaline, followed by the placement of an aortocaval shunt one week later. The mitoprotective compound SUL-150 (~6 mg·kg⁻¹·day⁻¹) or vehicle was administered intraperitoneally via osmotic minipump for 28 days, implanted at the time of aortocaval shunt placement. Vehicle-treated PAH rats had dyspnea and showed pulmonary artery remodeling with increased responsiveness to phenylephrine, in addition to remodeling of the intrapulmonary arterioles. SUL-150 administration mitigated the dyspnea and the remodeling responses. Vehicle-treated PAH rats developed right ventricular hypertrophy, fibrosis, and failure. SUL-150 administration precluded cardiomyocyte hypertrophy and inhibited ventricular fibrogenesis. Right ventricular failure in vehicle-treated PAH rats induced mitochondrial loss and dysfunction associated with a decrease in mitophagy. SUL-150 was unable to prevent the mitochondrial loss but improved mitochondrial health in the right ventricle, which culminated in the preservation of right ventricular function. We conclude that SUL-150 improves PAH-associated morbidity by the amelioration of pulmonary vascular remodeling and right ventricular failure and may be considered a promising therapeutic candidate to slow disease progression in pulmonary arterial hypertension and secondary right ventricular failure.

Multi-layer cell constructs produced in vitro are an innovative treatment option to support the growing demand for therapy in regenerative medicine. Our research introduces a novel construct integrating organ-derived decellularised extracellular matrix (dECM) hydrogels and 3D-printed biodegradable polymer meshes composed of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) to support and maintain multiple layers of different cell types. We achieved that by integrating the mechanical stability of PHBV+P34HB, commonly used in the food storage industry, with a dECM hydrogel, which replicates organ stiffness and supports cellular survival and function. The construct was customised by adjusting the fibre arrangement and pore sizes, making it a suitable candidate for a personalised design. We showed that the polymer is degradable after precoating it with PHB depolymerase (PhaZ), with complete degradation achieved in 3–5 days and delayed by adding the hydrogel to 10 days, enabling tuneable degradation for regenerative medicine applications. Finally, as a proof of concept, we composed a three-layered tissue in vitro; each layer represented a different tissue type: epidermal, vascular, and subcutaneous layers. Possible future applications include wound healing and diabetic ulcer paths, personalised drug delivery systems, and personalised tissue implants.