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

Lying between the endothelial beds of the body’s circulation is the interstitial microenviroment wherein the complex biohphysical and biochemical interplay of cells, extracellular matrix, and the molecules of interstitial 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. I hypothesize that the blood and lymphatic microvasculature, as gatekeepers to the interstitium and governors of molecular and fluid fluxes, regulate tissue homeostasis and 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 vasculature, 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 in lymphedema resulted in hyperproliferation, yet poor organization and decreased function of lymphatic capillaries. Where interstitial flow rates slowed 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 interstitium. 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 influences systemic metabolism.

No longer considered to be a passive reservoir, adipose tissue is an active metabolic player and dynamic endocrine organ. My current postdoctoral research at UT Southwestern Medical Center focuses on adipose tissue physiology and how the microvasculature may control its metabolism and inflammation via adipokine and metabolite transport. 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. In the laboratory of Prof. Philipp Scherer I have demonstrated that oligomer size, particularly that of the high molecular weight form, presents transport limitations across endothelial barriers with low intercellular permeabilities. I have quantified size-dependent exclusion of adiponectin oligomers in model endothelial cells in vitro, and used genetically- and metabolically-altered mouse models to discern that oligomer function likely depends on microvasculature permeabilities in vivo. Adiponectin transport, and potentially function, are pharmacologically and pathologically limited by endothelial function. I have demonstrated that metabolic stresses modulate the permeability of the vasculature for increased or decreased lipolytic fluxes with feeding and fasting, and endothelial dysfunction regulates 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 vasculature. One concomitant pathology with obesity is chronic kidney disease; changes 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, adiponectin altered renal recovery. Altering systemic fluid balance and interstitial fluxes pharmacolgically or by controlling renal physiology drives either adipogenesis or 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 take an integrative biomedical engineering approach to the important and relevant problem of obesity and metabolic dysfunction by combining and contributing to fundamental mechanistic insights in adipose tissue physiology, microvascular biology, and interstitial fluid mechanics. My laboratory will develop and utilize in vitro tissue engineered models to study the adipose biophysical environment and adipocyte interactions with blood and lymphatic endothelial cells. We will concurrently utilize relevant, targeted transgenic in vivo models to demonstrate the physiologic relevance of our in vitro advances.

Accepted Peer-Reviewed Publications

UT Southwestern Medical Center

Wernstedt Asterholm I, McDonald J, Blanchard PG, Sinha M, Xiao Q, Mistry J, Rutkowski JM, Dehaies Y, Brekken RA, Scherer PE. Lack of immunological fitness during fasting in metabolically challenged animals. J Lipid Res. 2012Apr 13.

Fischer-Posovszky P, Wang QA, Asterholm IW, Rutkowski JM, Scherer PE. Targeted deletion of adipocytes by apoptosis leads to adipose tissue recruitment of alternatively activated m2 macrophages. Endocrinology. 2011Aug;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 2011Jan;17(1):55-63.

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

École Polytechnique Fédérale de Lausanne (EPFL)

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. 2010Mar 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. 2010Mar;176(3):1122-9.

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. 2007Apr;21(4):1003-12. (* equal contribution)

Goldman J, Conley KA, Raehl A, Bondy DM, Pytowski B, Swartz MA, Rutkowski JM, Jaroch DB, Ongstad EL. Regulation of VEGF-C by interstitial flow. Am J Physiol Heart Circ Physiol. 2007May;292(5):H2176-83.

Rutkowski JM and Swartz MA. A driving force for change: Interstitial flow as a morphoregulator. Trends Cell Biol. 2007Jan;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. 2006Nov;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. 2006Sep;291(3):H1402-10.

Penn State University

Rutkowski JM, Santiago LY, Ben-Jebria, Ultman JS. Comparison of ozone-specific (OZAC) and oxygen radical (ORAC) antioxidant capacity assays for use with nasal lavage fluid. Toxicol In Vitro. 2011Oct;25(7):1406-13.

Rutkowski JM, Santiago LY, Ben-Jebria, Ultman JS. Development of an assay for ozone-specific antioxidant capacity. Inhal Toxicol. 2003 Nov;15(13):1369-85.