Molecular Mechanisms Controlling Lymphatic Vascular Function in Health and Disease

PROJECT SUMMARY/ABSTRACT
The lymphatic vascular system controls tissue fluid homeostasis and intestinal lipid uptake. Proper lymphatic
function positively correlates with favorable outcomes for patients with cardiovascular and metabolic disorders,
which accentuates the importance of this system in maintaining systemic homeostasis. Our long-term goal is to
uncover molecular mechanisms and critical regulators that govern lymphatic function in health and disease,
with the hope of offering new therapeutic targets to combat cardiovascular and metabolic diseases. In the
previous funding period, we discovered that the Forkhead Box C2 (Foxc2) transcription factor antagonizes
vascular endothelial growth factor receptor 3 (VEGFR3) signaling by inducing the expression of epsins;
endocytic adaptor proteins critical for VEGFR3 degradation and vascular endothelial growth factor C (VEGF-C)
signal attenuation in lymphatic endothelial cells (LECs). We also discovered that the Forkhead Box C2
transcription factor (Foxc2) was an important regulator of obesity and that restoration of lymphatic function was
a potential strategy to treat metabolic diseases. As a result, in this renewal application, we sought to identify
and study additional regulatory molecules of lymphatic function. We determined that the micro-ribonucleic acid
miR-22 regulates lymphatic function in normal and diseased conditions. Despite its prominence in governing
lymphatic pathophysiology, little is known about the role that miR-22 plays in regulating the function of this
vascular system. Consequently, we generated novel, inducible lymphatic endothelial cell (LEC)-specific miR-22
loss-of-function mice and discovered that the deficiency of this molecule dramatically increased developmental
lymphangiogenesis and increased the expression of the master regulator of lymphatic differentiation and fate
determination Prox1 as well as fortifying VEGF-C/VEGFR3 signaling and increasing the expression of
metabolic regulatory genes. Therefore, our central hypothesis is that lymphatic miR-22 represses Prox1,
constrains VEGFR3 signaling, and stymies energy production by suppressing metabolic programming.
Conversely, loss of lymphatic miR-22 elevates Prox1 expression, VEGFR-3 signaling, and metabolic
bioenergetics; thereby, mending impaired lymphangiogenesis and lymphatic function in cardiovascular and
metabolic disorders. To test our hypothesis and determine how miR-22 inhibition exerts a pro-lymphangiogenic
stimulus to ameliorate cardiovascular and metabolic disease, we propose the following related, but
independent, Specific Aims: 1) to determine the role of miR-22 in governing metabolic programming and
VEGFR3 signaling, 2) to determine molecular mechanisms by which miR-22 governs lymphatic function in the
adult, and 3) to determine the therapeutic potential of targeting miR-22 and epsins in lymphatic systems. Our
findings will identify novel molecular mechanisms underlying metabolic regulation and signaling to drive
reparative and regenerative lymphangiogenesis. We anticipate that therapies targeting miR-22 or epsins may
be valuable for restoring the injured lymphatic vasculature to treat cardiovascular and metabolic diseases.

Grant Number: 5R01HL133216-08
NIH Institute/Center: NIH
Principal Investigator: Hong Chen