No abstract

Lymphatic contractions play a fundamental role in maintaining tissue and organ homeostasis. The lymphatic system relies on orchestrated contraction of collecting lymphatic vessels, via lymphatic muscle cells and one-way valves, to transport lymph from the interstitial space back to the great veins, against an adverse pressure gradient. Circumferential stretch is known to regulate contractile function in collecting lymphatic vessels; however, less is known about the role of axial stretch in regulating contraction. It is likely that collecting lymphatic vessels are under axial strain in vivo and that the opening and closing of lymphatic valves leads to significant changes in axial strain throughout the pumping cycle. The purpose of this paper is to quantify the responsiveness of lympatic pumping to altered axial stretch. In situ measurements suggest that rat tail collecting lymphatic vessels are under an axial stretch of ~1.24 under normal physiological loads. Ex vivo experiments on isolated rat tail collecting lymphatics showed that the contractile metrics such as contractile amplitude, frequency, ejection fraction, and fractional pump flow are sensitive to axial stretch. Multiphoton microscopy showed that the predominant orientation of collagen fibers is in the axial direction, while lymphatic muscle cell nuclei and actin fibers are oriented in both circumferential and longitudinal directions, suggesting an axial component to contraction. Taken together, these results demonstrate the significance of axial stretch in lymphatic contractile function, suggest that axial stretch may play an important role in regulating lymph transport, and demonstrate that changes in axial strains could be an important factor in disease progression.

ObjectiveMicrovascular remodeling is governed by biomechanical and biochemical cues which are dysregulated in idiopathic pulmonary fibrosis. Understanding how these cues impact endothelial cell‐pericyte interactions necessitates a model system in which both variables can be independently and reproducibly modulated. In this study we develop a tunable hydrogel‐based angiogenesis assay to study how varying angiogenic growth factors and environmental stiffness affect sprouting and vessel organization.MethodsLungs harvested from mice were cut into 1 mm long segments then cultured on hydrogels having one of seven possible stiffness and growth factor combinations. Time course, brightfield, and immunofluorescence imaging were used to observe and quantify sprout formation.ResultsOur assay was able to support angiogenesis in a comparable manner to Matrigel in soft 2 kPa gels while enabling tunability to study the effects of stiffness on sprout formation. Matrigel and 2 kPa groups contained significantly more samples with sprouts when compared to the stiffer 10 and 20 kPa gels. Growth factor treatment did not have as obvious an effect, although the 20 kPa PDGF + FGF‐treated group had significantly longer vessels than the vascular endothelial growth factor‐treated group.ConclusionsWe have developed a novel, tunable hydrogel assay for the creation of lung explant vessel organoids which can be modulated to study the impact of specific environmental cues on vessel formation and maturation.

No abstract