Regulating Lymphatic Vasculature in Fibrosis: Understanding the Biology to Improve the Modeling

Age-related meningeal extracellular matrix remodeling compromises CNS lymphatic function

Efficient clearance of central nervous system (CNS) waste proteins and appropriate immune surveillance is essential for brain health. These processes are facilitated by lymphatic networks present in the meninges that drain cerebrospinal fluid (CSF). Age-related impairments to meningeal lymphatic drainage contribute to CNS waste accumulation and immune dysfunction, yet the underlying mechanisms remain poorly understood. Here, we identify extracellular matrix (ECM) remodeling in the aged dura as a key driver of CSF clearance deficits, demonstrating that peri-lymphatic collagen accumulation disrupts lymphatic function. Exploring immune-derived factors contributing to this ECM remodeling, we identify transforming growth factor beta 1 (TGFβ1) as a major regulator using primary human dural fibroblasts. Using a novel mouse model with constitutively active TGFβ receptor 1 (TGFβR1) signaling in dural fibroblasts, we show that excessive peri-lymphatic collagen deposition impairs meningeal lymphatic drainage and alters meningeal immunity. Mechanistically, we reveal that ECM-associated matrix stiffness disrupts lymphatic junction integrity and impairs lymphangiogenesis in human lymphatic endothelial cells. These findings establish dural immune cell and fibroblast-mediated ECM remodeling as a critical regulator of CSF clearance and highlight it as a potential therapeutic target for restoring brain waste clearance in aging.

Renal Interstitial Distribution of Full-Length IgG and Fab Fragments in Unilateral Ureteral Obstruction-Induced Fibrotic Kidneys

Renal fibrosis, a critical contributor to chronic kidney disease, is characterized by interstitial expansion and excessive extracellular matrix accumulation. Due to their specificity, monoclonal antibodies (mAbs) and their fragments are promising candidates for treating renal fibrosis, but their distribution characteristics in fibrotic kidneys, particularly within the renal interstitium, remain unclear. This study investigated the tissue distribution of full-length IgG and Fab fragments in a unilateral ureteral obstruction (UUO)-induced renal fibrosis mouse model. Full-length IgG and Fab fragments were intravenously administered in UUO-induced renal fibrosis model mice. The concentrations in each organ and plasma were quantified using enzyme-linked immunoassay. In addition, the localization within the renal interstitium was evaluated by multiple techniques, including intravital and ex vivo confocal imaging under near-living conditions and the observation of the tissue sections via an in vivo cryotechnique. Both full-length IgG and Fab fragments showed higher distribution in fibrotic kidneys than in other organs. Specifically, Fab fragments had excellent selective accumulation in the fibrotic kidneys, whereas full-length IgG had higher absolute distribution due to slower plasma elimination. Imaging assessments revealed that both had widespread localization within the interstitial spaces of the fibrotic kidneys. Due to their superior selectivity for fibrotic kidneys, Fab fragments can be used to target fibrotic lesions. Due to its prolonged distribution, full-length IgG may offer advantages in sustained therapeutic effects. This study provides foundational insights into the distribution of mAbs and their fragments in fibrotic kidneys and underscores the importance of further pharmacokinetic analyses to refine antibody-based therapies.

Therapeutically Induced Lymphangiogenesis Is Ineffective in Resolving Established Kidney Disease in Mice

Key Points

Background

CKD counts AKI as one of its many underlying causes. Lymphatic vessels are important in modulating inflammation postinjury. Manipulating lymphatic vessel expansion thus has the potential to alter CKD progression. Previously, we demonstrated that renal lymphatic expansion before injury reduced CKD progression after an AKI. Here, we test whether inducing lymphangiogenesis affects established CKD.

Methods

After CKD progression, kidney lymphatics were expanded by transgenic induction of kidney-specific overexpression of vascular endothelial growth factor-D in aristolochic acid (AA) nephropathy and cisplatin injury aggravated with chronic high phosphate diet (CisPi) models or by infusion of kidney-targeting nanoparticles loaded with the vascular endothelial growth factor receptor-3 specific ligand vascular endothelial growth factor-C C156S in a progressive proteinuria (POD) model. Renal fibrosis and lymphatic density were determined by picrosirius red staining and immunofluorescence, respectively. Renal function was assessed by creatinine clearance rate, serum creatinine, BUN, and urinary albumin-creatinine ratio. Renal proinflammatory and fibrotic markers expression were measured by quantitative RT-PCR.

Results

Kidney-specific overexpression of vascular endothelial growth factor-D+ mice demonstrated expanded renal lymphatics, while nanoparticles treatment minimally expanded lymphatics. In neither the AA nor POD model did lymphangiogenesis improve renal function or fibrosis. AA mice showed decreased Tgfb1 expression and POD mice showed increased Col4a1 expression. Expansion worsened function in CisPi CKD and increased fibrosis. CisPi kidneys also demonstrated increased expression of Mcp-1, Il1b, Col1a1, and Tgfb1 and increased macrophage numbers.

Conclusions

Therapeutically induced lymphatic expansion is ineffective in resolving established CKD and has the potential to further worsen CKD progression.

Chick Chorioallantoic Membrane as an in vivo Model for the Study of Angiogenesis and Lymphangiogenesis

BACKGROUND

The high incidence of vascular and lymphatic metastasis is closely associated with poor prognosis and mortality in cancer. Finding effective inhibitors to prevent pathological angiogenesis and lymphangiogenesis relies on appropriate in vivo models. The chick embryo chorioallantoic membrane (CAM) is formed by the fusion of the chorion and allantois during embryonic development.

SUMMARY

In this context, we primarily summarize the changes in vascular and lymphatic vessel formation in tumors under the action of drugs using this model, providing a preclinical model basis for effective tumor inhibitors.

KEY MESSAGES

Due to natural immunological defects, chick embryos accept various tissue and species transplants without immune response. The CAM model has been widely used in studying angiogenesis, antiangiogenesis, tumor growth, tumor metastasis, and drug efficacy. This review describes the use of CAM assays as a valuable method for testing the in vivo effects of drugs on vascular and lymphatic vessel formation before further investigating the effects of drugs on tumor vessels and lymphatic vessels in animal models.

BACKGROUND

The high incidence of vascular and lymphatic metastasis is closely associated with poor prognosis and mortality in cancer. Finding effective inhibitors to prevent pathological angiogenesis and lymphangiogenesis relies on appropriate in vivo models. The chick embryo chorioallantoic membrane (CAM) is formed by the fusion of the chorion and allantois during embryonic development.

SUMMARY

In this context, we primarily summarize the changes in vascular and lymphatic vessel formation in tumors under the action of drugs using this model, providing a preclinical model basis for effective tumor inhibitors.

KEY MESSAGES

Due to natural immunological defects, chick embryos accept various tissue and species transplants without immune response. The CAM model has been widely used in studying angiogenesis, antiangiogenesis, tumor growth, tumor metastasis, and drug efficacy. This review describes the use of CAM assays as a valuable method for testing the in vivo effects of drugs on vascular and lymphatic vessel formation before further investigating the effects of drugs on tumor vessels and lymphatic vessels in animal models.

Multi-parameter tunable synthetic matrix for engineering lymphatic vessels

Controlling the formation of new lymphatic vessels has been postulated as an innovative therapeutic strategy for various disease phenotypes, including neurodegenerative diseases, metabolic syndrome, cardiovascular disease, and lymphedema. Yet, compared to the blood vascular system, little is known about the molecular regulation that controls lymphatic tube formation in a synthetic matrix. In this study, we utilize hyaluronic acid (HA)-hydrogels to design a novel platform for decoupled investigation into how mechanical and biochemical cues regulate lymphatic vessel formation in a synthetic matrix. Using HA and controlling the degree of modification provides a method to preserve and modulate key lymphatic markers Prox1, LYVE-1, and Pdpn. The chemistry of the system allows for spatial and temporal patterning of specific peptides and substrate stiffnesses, and an MMP-sensitive crosslinker allowed cells to degrade and remodel their matrix. Through systematic optimization of multiple parameters, we have designed a system that allows human lymphatic endothelial cells (LECs) to self-assemble into vessels in vitro within 3 days. These engineered vessels can be cultured for up to 3 weeks and can be used for high-throughput mechanistic studies, or can be implanted into immunodeficient mice where they have demonstrated the ability to integrate and mature. Collectively, these studies report a novel, fully-defined 3D synthetic matrix system capable of generating lymphatic vessels in vitro that provide promise as an in vitro screening platform and as a therapeutic vessel transplant, which to our knowledge, is the first ever 3D lymphatic tissue engineering approach to not require the use of support cells.

Characterization of Photo-Crosslinked Methacrylated Type I Collagen as a Platform to Investigate the Lymphatic Endothelial Cell Response

Despite chronic fibrosis occurring in many pathological conditions, few in vitro studies examine how fibrosis impacts lymphatic endothelial cell (LEC) behavior. This study examined stiffening profiles of PhotoCol®-commercially available methacrylated type I collagen-photo-crosslinked with the photoinitiators: Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), Irgacure 2959 (IRG), and Ruthenium/Sodium Persulfate (Ru/SPS) prior to evaluating PhotoCol® permeability and LEC response to PhotoCol® at stiffnesses representing normal and fibrotic tissues. Ru/SPS produced the highest stiffness (~6 kilopascal (kPa)) for photo-crosslinked PhotoCol®, but stiffness did not change with burst light exposures (30 and 90 s). The collagen fibril area fraction increased, and dextran permeability (40 kilodalton (kDa)) decreased with photo-crosslinking, showing the impact of photo-crosslinking on microstructure and molecular transport. Human dermal LECs on softer, uncrosslinked PhotoCol® (~0.5 kPa) appeared smaller with less prominent vascular endothelial (VE)-cadherin (cell-cell junction) expression compared to LECs on stiffer PhotoCol® (~6 kPa), which had increased cell size, border irregularity, and VE-cadherin thickness (junction zippering) that is consistent with LEC morphology in fibrotic tissues. Our quantitative morphological analysis demonstrates our ability to produce LECs with a fibrotic phenotype, and the overall study shows that PhotoCol® with Ru/SPS provides the necessary physical properties to systematically study LEC responses related to capillary growth and function under fibrotic conditions.

Hyaluronic Acid Hydrogels with Phototunable Supramolecular Cross-Linking for Spatially Controlled Lymphatic Tube Formation

The dynamics of the extracellular matrix (ECM) influences stem cell differentiation and morphogenesis into complex lymphatic networks. While dynamic hydrogels with stress relaxation properties have been developed, many require detailed chemical processing to tune viscoelasticity, offering a limited opportunity for in situ and spatiotemporal control. Here, a hyaluronic acid (HA) hydrogel is reported with viscoelasticity that is controlled and spatially tunable using UV light to direct the extent of supramolecular and covalent cross-linking interactions. This is achieved using UV-mediated photodimerization of a supramolecular ternary complex of pendant trans-Brooker's Merocyanine (BM) guests and a cucurbit[8]uril (CB[8]) macrocycle. The UV-mediated conversion of this supramolecular complex to its covalent photodimerized form is catalyzed by CB[8], offering a user-directed route to spatially control hydrogel dynamics in combination with orthogonal photopatterning by UV irradiation through photomasks. This material thus achieves spatial heterogeneity of substrate dynamics, recreating features of native ECM without the need for additional chemical reagents. Moreover, these dynamic hydrogels afford spatial control of substrate mechanics to direct human lymphatic endothelial cells (LECs) to form lymphatic cord-like structures (CLS). Specifically, cells cultured on viscoelastic supramolecular hydrogels have enhanced formation of CLS, arising from increased expression of key lymphatic markers, such as LYVE-1, Podoplanin, and Prox1, compared to static elastic hydrogels prepared from fully covalent cross-linking. Viscoelastic hydrogels promote lymphatic CLS formation through the expression of Nrp2, VEGFR2, and VEGFR3 to enhance the VEGF-C stimulation. Overall, viscoelastic supramolecular hydrogels offer a facile route to spatially control lymphatic CLS formation, providing a tool for future studies of basic lymphatic biology and tissue engineering applications.