(3dr) Engineering In the Microvasculature: The Mechanical Microenvironment's Control of Systemic Metabolism

Lying between the endothelial beds of the body’s circulation is the interstial microenviroment wherein the complex biohphysical and biochemical interplay of cells, the extracellular matrix, and the molecules of interstital fluid control both immediate tissue homeostasis and systemic functions. The modulators of interstitial flow rates and shear, tissue hydration and composition, and cellular trafficking are the endothelial microvasculature of the blood and venous capillaries and the lymphatic system. As modulators of interstitial flow and molecular transport, the blood endothelial microvasculature and lymphatic system govern tissue homeostasis. I hypothesize that the blood and lymphatic microvasculature, as gatekeepers to the interstitium and governors of molecular and fluid fluxes, modulate metabolism through their endothelial physiology.

In my doctoral studies under Prof. Melody Swartz at the EPFL, we demonstrated that the primary modulator of interstitial drainage, the initial lymphatic vascualture, both controls the interstitium and cells found within and is itself modulated by the tissue mechnical environment. Generation of new functional lymphatic capillaries, lymphangiogenesis, was found to be directional and fully dependent on interstitial flow. Blocked lymphatic drainage, clinically the pathology of lymphedema, resulted in hyperproliferation, yet poor organization and decreased function of lymphatic capillaries. In the pathology of lymphedema, where intersitial flow rates slow towards zero, inflammatory chemokines accumulated, interstitial immune cells failed to traffick, and adipose tissue depots expanded in adipogenesis. Indeed, we quantified lymphatic clearance rates in genetic models of lymphatic dysfunction and found a correlation with fluid transport and remodeling of the extracellular matrix and adipose expansion on tissue hydraulic conductivities and subsequent treatment and potential resolution of the disease. Blood capillary extravasation, as controlled by Starling’s Law, was reduced in these instances due to the increased hydraulic and osmotic pressures of the interstitum. Concurrently, adipose expansion or hypercholesterolemia strongly reduced lymphatic drainage capability by inducing vessel degeneration. As lymphatic vessels are the primary route of lipid transport throughout the body, these studies combined to demonstrate the potential that the interplay of microvasculature cells with their surrounding tissues has to influence systemic metabolism.

My current postdoctoral research focuses on adipose tissue physiology and how the microvasculature may control its systemic functions via adipokine and metabolite transport. No longer considered to be a passive reservoir, adipose tissue is an active metabolic player and dynamic endocrine organ. The adipokine adiponectin, intruiging in that it is secreted in multiple oligomer sizes, has exhibited positive effects in regulation of systemic metabolism and insulin sensitivity through tissues such as liver, skeletal muscle, and centrally in the brain. In the laboratory of Prof. Philipp Scherer at UT Southwestern Medical Center we have found that oligomer size, particularly that of the high molecular weight form, presents transport limitations across endothelial barriers with low intercellular permeabilities such as in muscle or in the brain. We have quantified size-dependent exclusion of adiponectin oligomers in model endothelial cells in vitro, expressed adiponectin receptors in these cells to determine the role of ligand-receptor binding, and used genetic mouse models of receptor deletion in vivo to discern that oligomer function likely depends on microvasculature permeabilities (Podium 65e). We have altered these permeabilities, and subsequently adiponectin transport and potentially function, pharmacologically, pathologically, and with inducible transgenic in vivo models. Metabolic stresses modulate the permeability of the vasdculature for increased or decreased lipolytic fluxes and systemic adipokine effects. The critical barrier function of the endothelium thus modualtes multiple aspects of adipose function.

Ongoing studies are aimed at discerning the interplay between adipose tissue and its vaculature. One concomitant pathology with obesity is chronic kidney disease; hanges in renal function alter transvascular fluxes and protein concentrations in the periphery, resulting in excess fluid accumulation. In a recently developed inducible model of renal podocyte apoptosis (Poster 623ai), adiponectin altered renal recovery while ascites led to adipose wasting. Changes in lipid uptake or secretion coincide with altered adipokine profiles: all of which alter or are controlled by endothelial transport. I propose that the biophysical environment of adipose tissue, specifically matrix composition, interstitial flow, and lymphatic drainage, influence adipocyte behaviors and systemic metabolism and that changes in cell infiltration and chemokine levels in the interstitial fluid have a direct effect on adipogenesis, adipokine secretion, and metabolic lipid fluxes. My laboratory will develop and utilize in vitro tissue engineered models to study the adipose biophysical environment and relevant, targeted transgenic in vivo models to demonstrate the physiologic relevance of our in vitro advances.

Relevant Peer-Reviewed Publications:

Fischer-Posovszky P, Wang QA, Asterholm IW, Rutkowski JM, Scherer PE. Endocrinology. Targeted deletion of adipocytes by apoptosis leads to adipose tissue recruitment of alternatively activated m2 macrophages. 2011 Aug;152(8):3074-81.

Holland WL, Miller RA, Wang ZV, Sun K, Barth BM, Bui HH, Davis KE, Bikman BT, Halberg N, Rutkowski JM, Wade MR, Tenorio VM, Kuo MS, Brozinick JT, Zhang BB, Birnbaum MJ, Summers SA, Scherer PE. Receptor-mediated activation of ceramidase activity initiates the pleiotropic actions of adiponectin. Nat Med 2011 Jan;17(1):55-63.

Miteva DO, Rutkowski JM, Dixon JB, Kilarski W, Shields JD, Swartz MA. Transmural flow modulates cell and fluid transport functions of lymphatic endothelium. Circ Res. 2010 Mar 19;106(5):920-31.

Rutkowski JM, Markhus CE, Gyenge CC, Alitalo K, Wiig H, Swartz MA. Dermal matrix remodeling and fat accumulation control tissue swelling and hydraulic conductivity during murine primary lymphedema. Am J Pathol. 2010 Mar;176(3):1122-9.

Rutkowski JM, Davis KE, Scherer PE. Mechanisms of obesity and related pathologies: the macro- and microcirculation of adipose tissue. FEBS J. 2009 Oct;276(20):5738-46.

Lim HY, Rutkowski JM, Helft J, Reddy ST, Swartz MA, Randolph GJ, Angeli VA. Hypercholesterolemic mice exhibit lymphatic vessel dysfunction and degeneration. Am J Pathol. 2009 Sep;175(3):1328-37.

Goldman JG*, Rutkowski JM*, Shields JD*, Pasquier M, Cui Y, Schmökel HG, Pytowski B, Swartz MA. Co-operative and redundant roles of VEGFR-2 and VEGFR-3 signaling in adult lymphangiogenesis. FASEB J. 2007 Apr;21(4):1003-12. (* equal contribution)

Rutkowski JM and Swartz MA. A driving force for change: interstitial flow as a morphoregulator. Trends Cell Biol. 2007 Jan;17(1):44-50.

Rutkowski JM, Moya M, Johannes J, Goldman J, Swartz MA. Secondary lymphedema in the mouse tail: lymphatic hyperplasia, VEGF-C upregulation, and the protective role of MMP-9. Microvasc Res. 2006 Nov;72(3):161-71.

Rutkowski JM, Boardman KC, Swartz MA. Characterization of lymphangiogenesis in a model of adult skin regeneration. Am J Physiol Heart Circ Physiol. 2006 Sep;291(3):H1402-10.