adrenomedullin and Lymphedema

Secondary lymphedema is a debilitating condition, and genetic factors predisposing to its development remain largely unknown. Adrenomedullin (AM) is peptide encoded, together with proadrenomedullin N-terminal peptide (PAMP), by the Adm gene (adrenomedullin gene). AM and its putative receptor calcitonin receptor-like receptor (CLR) are implicated in angiogenesis and lymphangiogenesis during embryogenesis and wound healing, suggesting their possible involvement in secondary lymphedema. To investigate whether AM deficiency predisposes to secondary lymphedema, we used heterozygous adult mice with Adm gene-knockin stop mutation, which selectively abrogated AM, but preserved PAMP, expression (Adm(AM+/Δ) animals). After hind limb skin incision, Adm messenger RNA expression was upregulated in wounded tissue of both Adm(AM+/+) and Adm(AM+/Δ) mice. However, only Adm(AM+/Δ) animals developed limb swelling and histopathological lymphedematous changes, including epidermal thickening, elevated collagen fiber density, and increased microvessel diameter. Secondary lymphedema was prevented when circulating AM levels in Adm(AM+/Δ) mice were restored by systemic peptide delivery. In human skin, CLR was expressed in tissue components affected by lymphedema, including epidermis, lymphatics, and blood vessels. Our study identified a previously unrecognized role for endogenous AM as a key factor in secondary lymphedema pathogenesis and provided experimental in vivo evidence of an underlying germ-line genetic predisposition to developing this disorder.

Topics: Adrenomedullin; Animals; Calcitonin Receptor-Like Protein; Cells, Cultured; Endothelium, Lymphatic; Endothelium, Vascular; Gene Knock-In Techniques; Genetic Predisposition to Disease; Haploinsufficiency; Heterozygote; Humans; Lymphedema; Mice; Mice, Inbred C57BL; Mice, Mutant Strains; Mutation; Phenotype; Risk Factors

Adrenomedullin (AM) is a multifunctional peptide hormone that plays a significant role in vasodilation and angiogenesis. Lymphoedema is a common but refractory disorder that is difficult to be treated with conventional therapy. We therefore investigated whether AM promotes lymphangiogenesis and improves lymphoedema.. The effects of AM on lymphatic endothelial cells (LEC) were investigated. AM promoted proliferation, migration, and network formation of cultured human lymphatic microvascular endothelial cells (HLMVEC). AM increased intracellular cyclic adenosine monophosphate (cAMP) level in HLMVEC. The cell proliferation induced by AM was inhibited by a cAMP antagonist and mitogen-activated protein kinase kinase (MEK) inhibitors. Phosphorylated extracellular signal-regulated kinase (ERK) in HLMVEC was increased by AM. Continuous administration of AM (0.05 microg/kg/min) to BALB/c mice with tail lymphoedema resulted in a decrease in lymphoedema thickness. AM treatment increased the number of lymphatic vessels and blood vessels in the injury site.. AM promoted LEC proliferation at least in part through the cAMP/MEK/ERK pathway, and infusion of AM induced lymphangiogenesis and improved lymphoedema in mice.

Topics: Adrenomedullin; Animals; Cell Movement; Cell Proliferation; Cells, Cultured; Cyclic AMP; Disease Models, Animal; Endothelium, Lymphatic; Extracellular Signal-Regulated MAP Kinases; Humans; Lymphangiogenesis; Lymphedema; Male; Mice; Mice, Inbred BALB C; Mitogen-Activated Protein Kinase Kinases; Neovascularization, Physiologic; Signal Transduction; Vasodilation

Topics: Adrenomedullin; Animals; Cell Proliferation; Cells, Cultured; Disease Models, Animal; Endothelium, Lymphatic; Humans; Lymphangiogenesis; Lymphedema; Mice; Vasodilator Agents; Wound Healing

The lymphatic vascular system mediates fluid homeostasis, immune defense, and tumor metastasis. Only a handful of genes are known to affect the development of the lymphatic vasculature, and even fewer represent therapeutic targets for lymphatic diseases. Adrenomedullin (AM) is a multifunctional peptide vasodilator that transduces its effects through the calcitonin receptor-like receptor (calcrl) when the receptor is associated with a receptor activity-modifying protein (RAMP2). Here we report on the involvement of these genes in lymphangiogenesis. AM-, calcrl-, or RAMP2-null mice died mid-gestation after development of interstitial lymphedema. This conserved phenotype provided in vivo evidence that these components were required for AM signaling during embryogenesis. A conditional knockout line with loss of calcrl in endothelial cells confirmed an essential role for AM signaling in vascular development. Loss of AM signaling resulted in abnormal jugular lymphatic vessels due to reduction in lymphatic endothelial cell proliferation. Furthermore, AM caused enhanced activation of ERK signaling in human lymphatic versus blood endothelial cells, likely due to induction of CALCRL gene expression by the lymphatic transcriptional regulator Prox1. Collectively, our studies identify a class of genes involved in lymphangiogenesis that represent a pharmacologically tractable system for the treatment of lymphedema or inhibition of tumor metastasis.

Topics: Adrenomedullin; Animals; Calcitonin Receptor-Like Protein; Cell Proliferation; Embryo Loss; Embryonic Development; Endothelial Cells; Female; Homeodomain Proteins; Homeostasis; Intracellular Signaling Peptides and Proteins; Lymphatic Diseases; Lymphatic Vessels; Lymphedema; Male; MAP Kinase Signaling System; Membrane Proteins; Mice; Neoplasm Metastasis; Neoplasms; Neovascularization, Physiologic; Pregnancy; Receptor Activity-Modifying Protein 2; Receptor Activity-Modifying Proteins; Receptors, Calcitonin; Tumor Suppressor Proteins