Dysfunction of the lymphatic system is associated with a wide range of disease phenotypes. The restoration of dysfunctional lymphatic vessels has been hypothesized as an innovative method to rescue healthy phenotypes in diseased states including neurological conditions, metabolic syndromes, and cardiovascular disease. Compared

The lymphatic system is a major circulatory system within the body, responsible for the transport of interstitial fluid, waste products, immune cells, and proteins. Compared to other physiological systems, the molecular mechanisms and underlying disease pathology largely remain to be understood which has hindered advancements in therapeutic options for lymphatic disorders. Dysfunction of the lymphatic system is associated with a wide range of disease phenotypes and has also been speculated as a route to rescue healthy phenotypes in areas including cardiovascular disease, metabolic syndrome, and neurological conditions. This review will discuss lymphatic system functions and structure, cell sources for regenerating lymphatic vessels, current approaches for engineering lymphatic vessels, and specific therapeutic areas that would benefit from advances in lymphatic tissue engineering and regeneration.

Vascular endothelial growth factor C (VEGF-C) induces lymphangiogenesis via VEGF receptor-3 (VEGFR3), encoded by the most frequently mutated gene in human primary lymphedema. Angiopoietins (Angs) and their Tie receptors regulate lymphatic vessel development and mutations of the ANGPT2 gene were recently found in human primary lymphedema. However, the mechanistic basis of Ang2 activity in lymphangiogenesis is not fully understood. Here we used gene deletion, blocking antibodies, transgene induction and gene transfer to study how Ang2, its Tie2 receptor and Tie1 regulate lymphatic vessels. We discovered that VEGF-C-induced Ang2 secretion from lymphatic endothelial cells (LECs) is involved in full Akt activation downstream of phosphoinositide-3 kinase (PI3K). Neonatal deletion of genes encoding the Tie receptors or Ang2 in LECs, or administration of Ang2 blocking antibody decreased VEGFR3 presentation on LECs and inhibited lymphangiogenesis. A similar effect was observed in LECs upon deletion of PI3K catalytic p110α subunit or with small molecule inhibition of a constitutively active PI3K located downstream of Ang2. Deletion of Tie receptors or blockade of Ang2 decreased VEGF-C-induced lymphangiogenesis also in adult mice. Our results reveal important crosstalk between the VEGF-C and Ang signaling pathways and suggest new avenues for therapeutic manipulation of lymphangiogenesis by targeting Ang2-Tie-PI3K signaling.

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Fetal exposure to gestational diabetes mellitus (GDM) predisposes children to future health complications including type-2 diabetes mellitus, hypertension, and cardiovascular disease. A key mechanism by which these complications occur is through stress-induced dysfunction of endothelial progenitor cells (EPCs), including endothelial colony-forming cells (ECFCs). Although several approaches have been previously explored to restore endothelial function, their widespread adoption remains tampered by systemic side effects of adjuvant drugs and unintended immune response of gene therapies. Here, we report a strategy to rejuvenate circulating vascular progenitor cells by conjugation of drug-loaded liposomal nanoparticles directly to the surface of GDM-exposed ECFCs (GDM-ECFCs). Bioactive nanoparticles can be robustly conjugated to the surface of ECFCs without altering cell viability and key progenitor phenotypes. Moreover, controlled delivery of therapeutic drugs to GDM-ECFCs is able to normalize transgelin (TAGLN) expression and improve cell migration, which is a critical key step in establishing functional vascular networks. More importantly, sustained pseudo-autocrine stimulation with bioactive nanoparticles is able to improve in vitro and in vivo vasculogenesis of GDM-ECFCs. Collectively, these findings highlight a simple, yet promising strategy to rejuvenate GDM-ECFCs and improve their therapeutic potential. Promising results from this study warrant future investigations on the prospect of the proposed strategy to improve dysfunctional vascular progenitor cells in the context of other chronic diseases, which has broad implications for addressing various cardiovascular complications, as well as advancing tissue repair and regenerative medicine.