BACKGROUND: Transplant arteriosclerosis is a major complication in long-term survivors of heart transplantation. Increased lymph flow from donor heart to host lymph nodes has been reported to play a role in transplant arteriosclerosis, but how lymphangiogenesis affects this process is unknown. METHODS: Vascular allografts were transplanted among various combinations of mice, including wild-type, Lyve1 -CreER T2 ;R26-tdTomato, CAG-Cre-tdTomato, severe combined immune deficiency, Ccr2 KO , Foxn1 KO , and lghm / lghd KO mice. Whole-mount staining and 3-dimensional reconstruction identified lymphatic vessels within the grafted arteries. Lineage tracing strategies delineated the cellular origin of lymphatic endothelial cells. Adeno-associated viral vectors and a selective inhibitor were used to regulate lymphangiogenesis. RESULTS: Lymphangiogenesis within allograft vessels began at the anastomotic sites and extended from preexisting lymphatic vessels in the host. Tertiary lymphatic organs were identified in transplanted arteries at the anastomotic site and lymphatic vessels expressing CCL21 (chemokine [C-C motif] ligand 21) were associated with these immune structures. Fibroblasts in the vascular allografts released VEGF-C (vascular endothelial growth factor C), which stimulated lymphangiogenesis into the grafts. Inhibition of VEGF-C signaling inhibited lymphangiogenesis, neointima formation, and adventitial fibrosis of vascular allografts. These studies identified VEGF-C released from fibroblasts as a signal stimulating lymphangiogenesis extending from the host into the vascular allografts. CONCLUSIONS: Formation of lymphatic vessels plays a key role in the immune response to vascular transplantation. The inhibition of lymphangiogenesis may be a novel approach to prevent transplant arteriosclerosis.

Vascular aging is directly related to several major diseases including clinical primary hypertension. Conversely, elevated blood pressure itself accelerates vascular senescence. However, the interaction between vascular aging and hypertension have not been characterized during hypertensive aging. To depict the interconnectedness of complex mechanisms between hypertension and aging, we performed single-cell RNA sequencing of aorta, femoral and mesentery arteries, respectively from male Wistar Kyoto rats (WKY) and male spontaneously hypertensive rats (SHR) aging 16 or 72 weeks. We integrated 12 datasets to map the blood vessels of senile hypertension from three perspective: vascular aging, hypertension and vascular type. We found that aging and hypertension independently exerted a significant impact on the alteration of cellular composition and artery remodeling, even greater when superimposed. Consistently, smooth muscle cells (SMCs) underwent phenotypic switching from contractile towards synthetic, apoptotic and senescent SMCs with aging/hypertension. Furthermore, we identified three sub-clusters of Spp1  high, encoding protein osteopontin (OPN), synthetic SMCs, Spp1  high matrix-activated fibroblasts and Spp1  high scar-associated macrophage involved in hypertensive aging. Spp1  high scar-associated macrophage enriched for reactive oxygen species metabolic process and cell migration associated function. Cell-cell communication analysis revealed Spp1-Cd44 receptor pairing was markedly aggravated on hypertensive aging condition. Importantly, the concentration of serum OPN significantly potentiated in aged hypertensive patients compared with normal group. Thus, we provide a comprehensive cell atlas to systematically resolve the cellular diversity and dynamic cellular communication changes of the vessel wall during hypertensive aging, identifying a protein marker OPN as a potential regulator of vascular remodeling during hypertensive aging.

Lymphatic vessels, as the main tube network of fluid drainage and leukocyte transfer, are responsible for the maintenance of homeostasis and pathological repairment. Recently, by using genetic lineage tracing and single-cell RNA sequencing techniques, significant cognitive progress has been made about the impact of stem/progenitor cells during lymphangiogenesis. In the embryonic stage, the lymphatic network is primarily formed through self-proliferation and polarized-sprouting from the lymph sacs. However, the assembly of lymphatic stem/progenitor cells also guarantees the sustained growth of lymphvasculogenesis to obtain the entire function. In addition, there are abundant sources of stem/progenitor cells in postnatal tissues, including circulating progenitors, mesenchymal stem cells, and adipose tissue stem cells, which can directly differentiate into lymphatic endothelial cells and participate in lymphangiogenesis. Specifically, recent reports indicated a novel function of lymphangiogenesis in transplant arteriosclerosis and atherosclerosis. In the present review, we summarized the latest evidence about the diversity and incorporation of stem/progenitor cells in lymphatic vasculature during both the embryonic and postnatal stages, with emphasis on the impact of lymphangiogenesis in the development of vascular diseases to provide a rational guidance for future research.