Regulation of adipogenesis by lymphatic fluid stasis: part II. Expression of adipose differentiation genes

Lymphatic Vessel Network Structure and Physiology

The lymphatic system is comprised of a network of vessels interrelated with lymphoid tissue, which has the holistic function to maintain the local physiologic environment for every cell in all tissues of the body. The lymphatic system maintains extracellular fluid homeostasis favorable for optimal tissue function, removing substances that arise due to metabolism or cell death, and optimizing immunity against bacteria, viruses, parasites, and other antigens. This article provides a comprehensive review of important findings over the past century along with recent advances in the understanding of the anatomy and physiology of lymphatic vessels, including tissue/organ specificity, development, mechanisms of lymph formation and transport, lymphangiogenesis, and the roles of lymphatics in disease. © 2019 American Physiological Society. Compr Physiol 9:207-299, 2019.

Mesenteric Lymphatic Vessel Density Is Associated with Disease Behavior and Postoperative Recurrence in Crohn's Disease

PURPOSE

The aims of the present study were to examine the density of lymphatic vessels in the mesentery and to assess the predictive value of the mesenteric lymphatic vessel density for postoperative clinical recurrence.

METHODS

Ileocolonic resection specimens were obtained from 53 patients with Crohn's disease and 10 non-inflammatory bowel disease control subjects. Mesentery adipose tissues adjacent to the bowel wall were used for the histological quantification of lymphatic vessels using immunohistochemistry with the D2-40 antibody. The relationships between lymphatic vessel density and disease behavior, the presence of granulomas, the presence of creeping fat, and postoperative clinical recurrence were assessed.

RESULTS

Median lymphatic vessel density in the mesentery adjacent to inflamed or non-inflamed intestine was lower in control subjects than in Crohn's disease patients (2.13‰; interquartile range [IQR], 1.83-2.61; 8.34‰; IQR, 6.39-10.22; 4.43‰; IQR, 3.32-5.78; P ˂ 0.001). Increased mesenteric lymphatic vessel density was significantly associated with stricturing behavior, the presence of intestinal granulomas, the presence of creeping fat, and bowel thickness. Interestingly, patients with disease recurrence had an increased mesenteric lymphatic vessel density of the proximal mesenteric margin at the time of resection compared with those who did not have disease recurrence (6.23‰; IQR, 5.43-6.75 vs. 3.28‰; IQR, 2.93-4.29; P ˂ 0.001).

CONCLUSIONS

In addition to its correlation with disease behavior, bowel thickness, and the presence of intestinal granulomas and creeping fat, increased mesenteric lymphatic vessel density in the proximal margin is predictive of early clinical recurrence after surgery in patients with Crohn's disease.

Liposuction Gives Complete Reduction of Arm Lymphedema following Breast Cancer Treatment-A 5-year Prospective Study in 105 Patients without Recurrence

BACKGROUND

Arm lymphedema is a well-recognized complication after breast cancer surgery that negatively impacts patients' quality of life, both physiologically and psychologically. Lymph stasis and inflammation result in excess formation of adipose tissue, which makes removal of the deposited subcutaneous fat necessary to eliminate the excess volume. Liposuction, combined with postoperative controlled compression therapy (CCT), is the only treatment that gives complete reduction of the excess volume. The aim of this study was to evaluate the 5-year results after liposuction in combination with CCT.

METHODS

Patients consecutively operated on between 1993 and 2012 were identified from the lymphedema registry, comprising all patients with nonpitting lymphedema treated with liposuction and CCT in our department. Standardized forms were used to collect pre-, peri-, and postoperative data.

RESULTS

One hundred five women with nonpitting edema were treated. The mean interval between the breast cancer operation and lymphedema start was 2.9 ± 5.0 years, the mean duration of lymphedema was 10 ± 7.4 years, and the preoperative mean excess volume was 1,573 ± 645 ml. The mean volume aspirated was 1,831 ± 599 ml. Postoperative mean reduction 5 years postoperatively was 117% ± 26% as compared with the healthy arm.

CONCLUSION

Liposuction is an effective method for the treatment of chronic, nonpitting, arm lymphedema resistant to conservative treatment. The volume reduction remains complete after 5 years.

Liposuction Treatment of Lymphedema

In the Western world, lymphedema most commonly occurs following treatment of cancer. Limb reductions have been reported utilizing various conservative therapies including manual lymph and pressure therapy, as well as by microsurgical reconstruction involving lymphovenous shunts and transplantation of lymph vessels or nodes. Failure of these conservative and surgical treatments to provide complete reduction in patients with long-standing pronounced lymphedema is due to the persistence of excess newly formed subcutaneous adipose tissue in response to slow or absent lymph flow, which is not removed in patients with chronic non-pitting lymphedema. Traditional surgical regimes utilizing bridging procedures, total excision with skin grafting, or reduction plasty seldom achieved acceptable cosmetic and functional results. Liposuction removes the hypertrophied adipose tissue and is a prerequisite to achieve complete reduction, and this reduction is maintained long-term through constant (24 h) use of compression garments postoperatively. This article describes the techniques and evidence basis for the use of liposuction for treatment of lymphedema.

KLF2-mediated disruption of PPAR-γ signaling in lymphatic endothelial cells exposed to chronically increased pulmonary lymph flow

Lymphatic abnormalities associated with congenital heart disease are well described, yet the underlying mechanisms remain poorly understood. Using a clinically relevant ovine model of congenital heart disease with increased pulmonary blood flow, we have previously demonstrated that lymphatic endothelial cells (LECs) exposed in vivo to chronically increased pulmonary lymph flow accumulate ROS and have decreased bioavailable nitric oxide (NO). Peroxisome proliferator-activated receptor-γ (PPAR-γ), which abrogates production of cellular ROS by NADPH oxidase, is inhibited by Krüppel-like factor 2 (KLF2), a flow-induced transcription factor. We hypothesized that chronically increased pulmonary lymph flow induces a KLF2-mediated decrease in PPAR-γ and an accumulation of cellular ROS, contributing to decreased bioavailable NO in LECs. To better understand the mechanisms that transduce the abnormal mechanical forces associated with chronically increased pulmonary lymph flow, LECs were isolated from the efferent vessel of the caudal mediastinal lymph node of control ( n = 5) and shunt ( n = 5) lambs. KLF2 mRNA and protein were significantly increased in shunt compared with control LECs, and PPAR-γ mRNA and protein were significantly decreased. In control LECs exposed to shear forces in vitro, we found similar alterations to KLF2 and PPAR-γ expression. In shunt LECs, NADPH oxidase subunit expression was increased, and bioavailable NO was significantly lower. Transfection of shunt LECs with KLF2 siRNA normalized PPAR-γ, ROS, and bioavailable NO. Conversely, pharmacological inhibition of PPAR-γ in control LECs increased ROS equivalent to levels in shunt LECs at baseline. Taken together, these data suggest that one mechanism by which NO-mediated lymphatic function is disrupted after chronic exposure to increased pulmonary lymph flow is through altered KLF2-dependent PPAR-γ signaling, resulting in increased NADPH oxidase activity, accumulation of ROS, and decreased bioavailable NO. NEW & NOTEWORTHY Lymphatic endothelial cells, when exposed in vivo to chronically elevated pulmonary lymph flow in a model of congenital heart disease with increased pulmonary blood flow, demonstrate Krüppel-like factor 2-dependent disrupted peroxisome proliferator-activated receptor-γ signaling that results in the accumulation of reactive oxygen species and decreased bioavailable nitric oxide.

Lymphatic Dysfunction, Leukotrienes, and Lymphedema

The lymphatic system is essential for the maintenance of tissue fluid homeostasis, gastrointestinal lipid absorption, and immune trafficking. Whereas lymphatic regeneration occurs physiologically in wound healing and tissue repair, pathological lymphangiogenesis has been implicated in a number of chronic diseases such as lymphedema, atherosclerosis, and cancer. Insight into the regulatory mechanisms of lymphangiogenesis and the manner in which uncontrolled inflammation promotes lymphatic dysfunction is urgently needed to guide the development of novel therapeutics: These would be designed to reverse lymphatic dysfunction, either primary or acquired. Recent investigation has demonstrated the mechanistic role of leukotriene B₄ (LTB₄) in the molecular pathogenesis of lymphedema. LTB₄, a product of the innate immune response, is a constituent of the eicosanoid inflammatory mediator family of molecules that promote both physiological and pathological inflammation. Here we provide an overview of lymphatic development, the pathophysiology of lymphedema, and the role of leukotrienes in lymphedema pathogenesis.

The Lymphatic Vasculature: Its Role in Adipose Metabolism and Obesity

Obesity is a key risk factor for metabolic and cardiovascular diseases, and although we understand the mechanisms regulating weight and energy balance, the causes of some forms of obesity remain enigmatic. Despite the well-established connections between lymphatics and lipids, and the fact that intestinal lacteals play key roles in dietary fat absorption, the function of the lymphatic vasculature in adipose metabolism has only recently been recognized. It is well established that angiogenesis is tightly associated with the outgrowth of adipose tissue, as expanding adipose tissue requires increased nutrient supply from blood vessels. Results supporting a crosstalk between lymphatic vessels and adipose tissue, and linking lymphatic function with metabolic diseases, obesity, and adipose tissue, also started to accumulate in the last years. Here we review our current knowledge of the mechanisms by which defective lymphatics contribute to obesity and fat accumulation in mouse models, as well as our understanding of the lymphatic-adipose tissue relationship.

A vicious circle in chronic lymphoedema pathophysiology? An adipocentric view

Chronic lymphoedema is a disease caused by a congenital or acquired damage to the lymphatic system and characterized by complex chains of pathophysiologic events such as lymphatic fluid stasis, chronic inflammation, lymphatic vessels impairment, adipose tissue deposition and fibrosis. These events seem to maintain and reinforce themselves through a positive feedback loop: regardless of the initial cause of lymphatic stasis, the dysfunctional adipose tissue and its secretion products can worsen lymphatic vessels' function, aggravating lymph leakage and stagnation, which can promote further adipose tissue deposition and fibrosis, similar to what may happen in obesity. In addition to the current knowledge about the tight and ancestral interrelation between immunity system and metabolism, there is evidence for similarities between obesity-related and lymphatic damage-induced lymphoedema. Together, these observations indicate strong reciprocal relationship between lymphatics and adipose tissue and suggest a possible key role of the adipocyte in the pathophysiology of chronic lymphoedema's vicious circle.

Lymphedema Leads to Fat Deposition in Muscle and Decreased Muscle/Water Volume After Liposuction: A Magnetic Resonance Imaging Study

Background: Lymphedema leads to adipose tissue deposition. Water–fat magnetic resonance imaging (MRI) can quantify and localize fat and water. The presence of excess fat and excess water/muscle in the subfascial compartment of the lymphedematous limb has not been investigated before. The aim of this study was to investigate epifascial and subfascial fat and water contents in patients with chronic lymphedema before and after liposuction.

Methods and Results: Seven patients with arm lymphedema and six with leg lymphedema were operated on. The limbs were examined with water–fat MRI before liposuction (baseline) and at five time points. Complete reduction of the excess limb volumes was achieved. The excess epifascial fat was evident in the edematous limbs and a drop was seen following surgery. There were differences in excess water at all time points. At 1 year there was a decrease in excess water. Excess subfascial fat was seen in the edematous limbs at all time points. Subfascial excess water/muscle did not show any differences after surgery. However, starting from 3 months there was less subfascial water/muscle compared with baseline.

Conclusions: Subfascial fat in the lymphedematous limbs did not change. In contrast, the water in the subfascial compartment was reduced over time, which may represent a decrease of muscle volume after treatment due to less mechanical load after liposuction. Using water–fat MRI-based fat quantification, the fat and water contents may be quantified and localized in the various compartments in lymphedema.

Pathological changes of adipose tissue in secondary lymphoedema

BACKGROUND

The pathophysiology of lymphoedema is poorly understood. Current treatment options include compression therapy, resection, liposuction and lymphatic microsurgery, but determining the optimal treatment approach for each patient remains challenging.

OBJECTIVES

We characterized skin and adipose tissue alterations in the setting of secondary lymphoedema.

METHODS

Morphological and histopathological evaluations were conducted for 70 specimens collected from 26 female patients with lower-extremity secondary lymphoedema following surgical intervention for gynaecological cancers. Indocyanine green lymphography was performed for each patient to assess lymphoedema severity.

RESULTS

Macroscopic and ultrasound findings revealed that lymphoedema adipose tissue had larger lobules of adipose tissue, with these lobules surrounded by thick collagen fibres and interstitial lymphatic fluid. In lymphoedema specimens, adipocytes displayed hypertrophic changes and more collagen fibre deposits when examined using electron microscopy, whole-mount staining and immunohistochemistry. The number of capillary lymphatic channels was also found to be increased in the dermis of lymphoedema limbs. Crown-like structures (dead adipocytes surrounded by M1 macrophages) were less frequently seen in lymphoedema samples. Flow cytometry revealed that, among the cellular components of adipose tissue, adipose-derived stem/stromal cells and M2 macrophages were decreased in number in lymphoedema adipose tissue compared with normal controls.

CONCLUSIONS

These findings suggest that long-term lymphatic volume overload can induce chronic tissue inflammation, progressive fibrosis, impaired homeostasis, altered remodelling of adipose tissue, impaired regenerative capacity and immunological dysfunction. Further elucidation of the pathophysiological mechanisms underlying lymphoedema will lead to more reliable therapeutic strategies.

Lymphangiogenesis: fuel, smoke, or extinguisher of inflammation's fire?

Lymphangiogenesis is a recognized hallmark of inflammatory processes in tissues and organs as diverse as the skin, heart, bowel, and airways. In clinical and animal models wherein the signaling processes of lymphangiogenesis are manipulated, most studies demonstrate that an expanded lymphatic vasculature is necessary for the resolution of inflammation. The fundamental roles that lymphatics play in fluid clearance and immune cell trafficking from the periphery make these results seemingly obvious as a mechanism of alleviating locally inflamed environments: the lymphatics are simply providing a drain. Depending on the tissue site, lymphangiogenic mechanism, or induction timeframe, however, evidence shows that inflammation-associated lymphangiogenesis (IAL) may worsen the pathology. Recent studies have identified lymphatic endothelial cells themselves to be local regulators of immune cell activity and its consequential phenotypes - a more active role in inflammation regulation than previously thought. Indeed, results focusing on the immunocentric roles of peripheral lymphatic function have revealed that the basic drainage task of lymphatic vessels is a complex balance of locally processed and transported antigens as well as interstitial cytokine and immune cell signaling: an interplay that likely defines the function of IAL. This review will summarize the latest findings on how IAL impacts a series of disease states in various tissues in both preclinical models and clinical studies. This discussion will serve to highlight some emerging areas of lymphatic research in an attempt to answer the question relevant to an array of scientists and clinicians of whether IAL helps to fuel or extinguish inflammation. Impact statement Inflammatory progression is present in acute and chronic tissue pathologies throughout the body. Lymphatic vessels play physiological roles relevant to all medical fields as important regulators of fluid balance, immune cell trafficking, and immune identity. Lymphangiogenesis is often concurrent with inflammation and can potentially aide or worsen disease progression. How new lymphatic vessels impact inflammation and by which mechanism is an important consideration in current and future clinical therapies targeting inflammation and/or vasculogenesis. This review identifies, across a range of tissue-specific pathologies, the current understanding of inflammation-associated lymphangiogenesis in the progression or resolution of inflammation.

Therapeutic effects of hyaluronidase on acquired lymphedema using a newly developed mouse limb model

Acquired lymphedema is one of the most dreaded side effects of cancer treatment, such as surgical treatment or irradiation. However, due to the lack of appropriate animal models, there is no effective therapeutic method to cure acquired lymphedema. To develop a reproducible acquired lymphedema animal model, we devised a mouse hind limb model by removing a superficial inguinal lymph node, a popliteal lymph node, a deep inguinal lymph node, and the femoral lymphatic vessel. We measured the volume of lymphedematous leg and observed the change in level of hyaluronic acid (HA) and lymphangiogenic factors after injecting hyaluronidase. Our model showed the distinguishable swelling and the reliable symptoms compared to previously reported models. In the lymphedematous regions of our model, we confirmed that HA, a major component of extracellular matrix, accumulated to higher levels than in a normal mouse. This lymphedema volume was rapidly reduced by treating hyaluronidase. Following hyaluronidase injection, the lymphedematous region of our model resembled a normal hind limb. Our findings indicated that hyaluronidase promoted lymphangiogenesis on the lymphedematous limb. Based on hyaluronidase treatment in the lymphedematous region, this could potentially be a new therapeutic approach for acquired lymphedema mediated through the modification of the size of HA fragments. Impact statement In this manuscript, the essence of the work described in this manuscript involves the development of (1) a mouse limb model showing acquired lymphedema and (2) a potent therapeutic treatment using hyaluronidase to remedy acquired lymphedema in our model. In order to develop a reproducible acquired lymphedema animal model that reflects the most common symptoms experienced by lymphedema patients, we devised a mouse hind limb model by removing lymph nodes and lymphatics. Our model showed the distinguishable swelling and the reliable symptoms compared to previously reported models. In the lymphedematous regions of our model, we confirmed that hyaluronic acid (HA) accumulated to higher levels than in a normal mouse. This lymphedema volume was rapidly reduced by treating the lymphedematous leg with hyaluronidase, which also degraded high molecular weight HA to low molecular weight HA. Immunohistochemical analysis, quantitative real-time PCR analysis and lymphangioscintigraphy showed that hyaluronidase enhanced lymphangiogenesis in the lymphedematous limb.

Pathophysiology of lymphedema-Is there a chance for medication treatment?

Lymphedema is a common morbid after cancer treatment. The disease characterizes with progressive inflammatory process that result in irreversible fibrosis. Its chronology and progressive disease character often impacts the quality of life of cancer survivors. The pathophysiology of lymphedema remains unclear and the disease remains non-curable. In this article, we reviewed available studies of lymphedema and concluded possible treatment strategies for lymphedema. J. Surg. Oncol. 2017;115:96-98. © 2016 Wiley Periodicals, Inc.

Lymph Node Transplantation Decreases Swelling and Restores Immune Responses in a Transgenic Model of Lymphedema

INTRODUCTION

Secondary lymphedema is a common complication of cancer treatment and recent studies have demonstrated that lymph node transplantation (LNT) can decrease swelling, as well as the incidence of infections. However, although these results are exciting, the mechanisms by which LNT improves these pathologic findings of lymphedema remain unknown. Using a transgenic mouse model of lymphedema, this study sought to analyze the effect of LNT on lymphatic regeneration and T cell-mediated immune responses.

METHODS

We used a mouse model in which the expression of the human diphtheria toxin receptor is driven by the FLT4 promoter to enable the local ablation of the lymphatic system through subdermal hindlimb diphtheria toxin injections. Popliteal lymph node dissection was subsequently performed after a two-week recovery period, followed by either orthotopic LNT or sham surgery after an additional two weeks. Hindlimb swelling, lymphatic vessel regeneration, immune cell trafficking, and T cell-mediated immune responses were analyzed 10 weeks later.

RESULTS

LNT resulted in a marked decrease in hindlimb swelling, fibroadipose tissue deposition, and decreased accumulation of perilymphatic inflammatory cells, as compared to controls. In addition, LNT induced a marked lymphangiogenic response in both capillary and collecting lymphatic vessels. Interestingly, the resultant regenerated lymphatics were abnormal in appearance on lymphangiography, but LNT also led to a notable increase in dendritic cell trafficking from the periphery to the inguinal lymph nodes and improved adaptive immune responses.

CONCLUSIONS

LNT decreases pathological changes of lymphedema and was shown to potently induce lymphangiogenesis. Lymphatic vessels induced by LNT were abnormal in appearance, but were functional and able to transport antigen-presenting cells. Animals treated with LNT have an increased ability to mount T cell-mediated immune responses when sensitized to antigens in the affected hindlimb.

Hyperplasia, de novo lymphangiogenesis, and lymphatic regression in mice with tissue-specific, inducible overexpression of murine VEGF-D

Lymphatic vessels modulate tissue fluid balance and inflammation and provide a conduit for endocrine and lipid transport. The growth of new lymphatic vessels in the adult, lymphangiogenesis, is predominantly mediated through vascular endothelial growth factor receptor-3 (VEGFR-3) signaling. We took advantage of the unique binding of murine VEGF-D specifically to VEGFR-3 and generated mice capable of inducible, tissue-specific expression of murine VEGF-D under a tightly-controlled tetracycline response element (TRE) promoter to stimulate adult tissue lymphangiogenesis. With doxycycline-activated expression, TRE-VEGF-D mouse crossed to mice with tissue-specific promoters for the lung [Clara cell secretory protein-reverse tetracycline transactivator (rtTA)] developed pulmonary lymphangiectasia. In the kidney, (kidney-specific protein-rtTA × TRE-VEGF-D) mice exhibited rapid lymphatic hyperplasia on induction of VEGF-D expression. Crossed with adipocyte-specific adiponectin-rtTA mice [Adipo-VEGF-D (VD)], chronic VEGF-D overexpression was capable of inducing de novo lymphangiogenesis in white adipose tissue and a massive expansion of brown adipose tissue lymphatics. VEGF-D expression in white adipose tissue also increased macrophage infiltration and tissue fibrosis in the tissue. Expression did not, however, measurably affect peripheral fluid transport, the blood vasculature, or basal metabolic parameters. On removal of the doxycycline stimulus, VEGF-D expression returned to normal, and the expanded adipose tissue lymphatics regressed in Adipo-VD mice. The inducible TRE-VEGF-D mouse thus provides a novel murine platform to study the adult mechanisms and therapies of an array of disease- and tissue-specific models of lymphangiogenesis.

Lipidomic Profiling of Adipose Tissue Reveals an Inflammatory Signature in Cancer-Related and Primary Lymphedema

Cancer-related and primary lymphedema (LE) are associated with the production of adipose tissue (AT). Nothing is known, however, about the lipid-based molecules that comprise LE AT. We therefore analyzed lipid molecules in lipoaspirates and serum obtained from LE patients, and compared them to lipoaspirates from cosmetic surgery patients and healthy control cohort serum. LE patient serum analysis demonstrated that triglycerides, HDL- and LDL-cholesterol and lipid transport molecules remained within the normal range, with no alterations in individual fatty acids. The lipidomic analysis also identified 275 lipid-based molecules, including triacylglycerides, diacylglycerides, fatty acids and phospholipids in AT oil and fat. Although the majority of lipid molecules were present in a similar abundance in LE and non-LE samples, there were several small changes: increased C20:5-containing triacylglycerides, reduced C10:0 caprinic and C24:1 nervonic acids. LE AT oil also contained a signature of increased cyclopropane-type fatty acids and inflammatory mediators arachidonic acid and ceramides. Interestingly C20:5 and C22:6 omega-3-type lipids are increased in LE AT, correlating with LE years. Hence, LE AT has a normal lipid profile containing a signature of inflammation and omega-3-lipids. It remains unclear, however, whether these differences reflect a small-scale global metabolic disturbance or effects within localised inflammatory foci.

External Volume Expansion Modulates Vascular Growth and Functional Maturation in a Swine Model

Despite increasing application of the pre-grafting expansion during autologous fat transplantation in breast reconstruction, little is known about its mechanism of action. To address that, ventral skins of miniature pigs were treated over a 10-day or 21-day period, with continuous suction at −50 mm Hg via a 7-cm diameter rubber-lined suction-cup device. Soft tissue thickness increased immediately after this external volume expansion (EVE) treatment, such increase completely disappeared by the next day. In the dermis and subcutaneous fat, the EVE treated groups showed significant increases in blood vessel density evident by CD31 staining as well as in vascular networks layered with smooth muscle cells when compared with the control group. This finding was corroborated by the increased percentage of endothelial cells present in the treatment groups. There was no significant difference in the percentages of proliferating basal keratinocytes or adipocytes, nor in epidermal thickness. Moreover, the EVE had no effect on proliferation or differentiation potential of adipose stem cells. Taken together, the major effects of EVE appeared to be vascular remodeling and maturation of functional blood vessels. This understanding may help clinicians optimize the vascularity of the recipient bed to further improve fat graft survival.

Restoration of lymphatic function rescues obesity in Prox1-haploinsufficient mice

Prox1 heterozygous mice have a defective lymphatic vasculature and develop late-onset obesity. Chyle abnormally leaks from those vessels, accumulates in the surrounding tissues, and causes an increase in adipose tissue. We characterized the lymphatics of Prox1^+/- mice to determine whether the extent of obesity correlated with the severity of lymphatic defects. The lymphatic vasculature in Prox1^+/- mice exhibited reduced tracer clearance from the ear skin, dysfunctional perfusion of the lower legs, and reduced tracer uptake into the deep lymphatic collectors during mechanostimulation prior to the onset of obesity. Ear lymphatic vessels and leg collectors in Prox1^+/- mice were disorganized and irregular, further confirming that defective lymphatic vessels are associated with obesity in Prox1^+/- mice. We now provide conclusive in vivo evidence that demonstrates that leaky lymphatics mediate obesity in Prox1^+/- mice, as restoration of lymphatic vasculature function was sufficient to rescue the obesity features in Prox1^+/- mice. Finally, depth-lipomic profiling of lymph contents showed that free fatty acids induce adipogenesis in vitro.

Lymphedema surgery: Patient selection and an overview of surgical techniques

Evaluation of the lymphedema patients with appropriate staging is fundamental for further treatment. Treatment includes compressive decongestive therapy for stage 0 and 1 patients, lymphovenous anastomosis for stage 1 and 2 patients, vascularized lymph node transfer for stage 2 and above patients. Wedge resection, liposuction, and the Charles procedure are alternatives or additions to physiological procedures. The selection of donor lymph node flap and recipient site depends on the patient's lymphedema status and surgeon's expertise. J. Surg. Oncol. 2016;113:923-931. © 2016 Wiley Periodicals, Inc.

Higher vascular endothelial growth factor-C concentration in plasma is associated with increased forearm capillary filtration capacity in breast cancer-related lymphedema

Breast cancer-related lymphedema (BCRL) is a frequent, chronic and debilitating swelling that mainly affects the ipsilateral arm and develops as a complication to breast cancer treatment. The pathophysiology is elusive opposing development of means for prediction and treatment. We have earlier shown that the forearm capillary filtration coefficient (CFC) is increased bilaterally in BCRL. In this study, we aimed to elucidate if increased CFC is associated with low-grade inflammation and/or vascular endothelial growth factor-c (VEGF-C) signaling. Fourteen patients with unilateral BCRL and nine matched breast cancer controls without BCRL participated. Forearm CFC was measured by venous congestion strain gauge plethysmography, and suction blisters were induced medially on the upper arms. Concentrations of 17 selected cytokines, VEGF-C, and total protein were measured in blister fluid and in plasma. Forearm CFC was higher bilaterally in BCRL subjects (P ≤ 0.036). No differences between forearms were found in either group. Plasma VEGF-C concentrations were significantly higher in the BCRL subjects (P < 0.001). In BCRL subjects, monocyte chemotactic protein 1 (MCP-1) (P = 0.009) and total protein (P = 0.035) concentrations were higher in blister fluid from edematous arms compared with nonedematous arms. No differences were found in interstitial cytokine or total protein concentrations between arms in control subjects. Higher plasma concentration of VEGF-C is a possible cause of bilaterally increased forearm CFC in BCRL subjects. Interstitially increased MCP-1 levels may augment local microvascular protein permeability in BCRL.

Bridging the divide between pathogenesis and detection in lymphedema

While our understanding of the lymphatic system has improved substantially in the past few decades, the translation of this knowledge into improved healthcare solutions for patients suffering from secondary lymphedema has been severely limited. The challenge facing clinicians is two-fold. First, there is no reliable, affordable, diagnostic capable of detecting the disease before symptoms of the lymphedema develop and the efficacy of treatment options becomes limited. Second, our understanding of the disease pathogenesis, its risk factors, and the underlying physiologic mechanisms is still in its infancy. These two challenges go hand in hand as limited diagnostic options have hindered our ability to understand lymphedema progression, and the lack of known underlying mechanisms involved in the disease prohibits the development of new diagnostic targets. This review serves to discuss the recent developments in clinical and lab research settings of both lymphedema diagnostic technologies and our understanding of the mechanisms driving disease risk and progression. We will show how these two lines of research are synergistically working with the ultimate goal of improving patient outcomes for those suffering from this horrible disease, identifying key areas of further research that are warranted to move the field forward and provide clinical relief for this neglected patient population.

Lymphedema fat graft: an ideal filler for facial rejuvenation

Lymphedema is a chronic disorder characterized by lymph stasis in the subcutaneous tissue. Lymphatic fluid contains several components including hyaluronic acid and has many important properties. Over the past few years, significant research has been performed to identify an ideal tissue to implant as a filler. Because of its unique composition, fat harvested from the lymphedema tissue is an interesting topic for investigation and has significant potential for application as a filler, particularly in facial rejuvenation. Over a 36-month period, we treated and assessed 8 patients with lymphedematous limbs who concurrently underwent facial rejuvenation with lymphedema fat (LF). We conducted a pre- and post-operative satisfaction questionnaire survey and a histological assessment of the harvested LF fat. The overall mean general appearance score at an average of 6 months after the procedure was 7.2±0.5, demonstrating great improvement. Patients reported significant improvement in their skin texture with a reading of 8.5±0.7 and an improvement in their self-esteem. This study demonstrates that LF as an ideal autologous injectable filler is clinically applicable and easily available in patients with lymphedema. We recommend the further study and clinical use of this tissue as it exhibits important properties and qualities for future applications and research.

An abnormal lymphatic phenotype is associated with subcutaneous adipose tissue deposits in Dercum's disease

OBJECTIVE

Investigational, near-infrared fluorescence (NIRF) lymphatic imaging was used to assess lymphatic architecture and contractile function in participants diagnosed with Dercum's disease, a rare, poorly understood disorder characterized by painful lipomas in subcutaneous adipose tissues.

METHODS

After informed consent and as part of an FDA-approved feasibility study to evaluate lymphatics in diseases in which their contribution has been implicated, three women diagnosed with Dercum's disease and four control subjects were imaged. Each participant received multiple intradermal and subcutaneous injections of indocyanine green (ICG, total dose ≤400 µg) in arms, legs, and/or trunk. Immediately after injection, ICG was taken up by the lymphatics and NIRF imaging was conducted.

RESULTS

The lymphatics in the participants with Dercum's disease were intact and dilated, yet sluggishly propelled lymph when compared to control lymphatics. Palpation of regions containing fluorescent lymphatic pathways revealed tender, fibrotic, tubular structures within the subcutaneous adipose tissue that were associated with painful nodules, and, in some cases, masses of fluorescent tissue indicating that some lipomas may represent tertiary lymphoid tissues.

CONCLUSIONS

These data support the hypothesis that Dercum's disease may be a lymphovascular disorder and suggest a possible association between abnormal adipose tissue deposition and abnormal lymphatic structure and function.

Lymphedema and obesity: is there a link?

Lymphedema is a chronic disorder that, in developed countries, occurs most commonly after lymph node dissection for cancer treatment. Although the pathophysiology of lymphedema is unknown, the disease is characterized histologically by fibrosis and abnormal adipose deposition. Clinical studies have provided evidence that obesity and postoperative weight gain are significant risk factors for the development of lymphedema. In fact, recent studies have shown that extreme obesity can result in markedly impaired lymphatic function and primary lymphedema. The aim of this Special Topic article is to review evidence linking obesity and lymphedema. In addition, the authors review recent studies that have analyzed the cellular mechanisms that may be responsible for this relationship, with a goal of highlighting areas of research that may have significant translational potential.

Diffusion and perfusion: the keys to fat grafting

BACKGROUND

Fat grafting is now widely used in plastic surgery. Long-term graft retention can be unpredictable. Fat grafts must obtain oxygen via diffusion until neovascularization occurs, so oxygen delivery may be the overarching variable in graft retention.

METHODS

We studied the peer-reviewed literature to determine which aspects of a fat graft and the microenvironment surrounding a fat graft affect oxygen delivery and created 3 models relating distinct variables to oxygen delivery and graft retention.

RESULTS

Our models confirm that thin microribbons of fat maximize oxygen transport when injected into a large, compliant, well-vascularized recipient site. The "Microribbon Model" predicts that, in a typical human, fat injections larger than 0.16 cm in radius will have a region of central necrosis. Our "Fluid Accommodation Model" predicts that once grafted tissues approach a critical interstitial fluid pressure of 9 mm Hg, any additional fluid will drastically increase interstitial fluid pressure and reduce capillary perfusion and oxygen delivery. Our "External Volume Expansion Effect Model" predicts the effect of vascular changes induced by preoperative external volume expansion that allow for greater volumes of fat to be successfully grafted.

CONCLUSIONS

These models confirm that initial fat grafting survival is limited by oxygen diffusion. Preoperative expansion increases oxygen diffusion capacity allowing for additional graft retention. These models provide a scientific framework for testing the current fat grafting theories.

Obesity increases inflammation and impairs lymphatic function in a mouse model of lymphedema

Although obesity is a major clinical risk factor for lymphedema, the mechanisms that regulate this effect remain unknown. Recent reports have demonstrated that obesity is associated with acquired lymphatic dysfunction. The purpose of this study was to determine how obesity-induced lymphatic dysfunction modulates the pathological effects of lymphatic injury in a mouse model. We used a diet-induced model of obesity in adult male C57BL/6J mice in which experimental animals were fed a high-fat diet and control animals were fed a normal chow diet for 8-10 wk. We then surgically ablated the superficial and deep lymphatics of the midportion of the tail. Six weeks postoperatively, we analyzed changes in lymphatic function, adipose deposition, inflammation, and fibrosis. We also compared responses to acute inflammatory stimuli in obese and lean mice. Compared with lean control mice, obese mice had baseline decreased lymphatic function. Lymphedema in obese mice further impaired lymphatic function and resulted in increased subcutaneous adipose deposition, increased CD45(+) and CD4(+) cell inflammation (P < 0.01), and increased fibrosis, but caused no change in the number of lymphatic vessels. Interestingly, obese mice had a significantly increased acute inflammatory reaction to croton oil application. In conclusion, obese mice have impaired lymphatic function at baseline that is amplified by lymphatic injury. This effect is associated with increased chronic inflammation, fibrosis, and adipose deposition. These findings suggest that obese patients are at higher risk for lymphedema due to impaired baseline lymphatic clearance and an increased propensity for inflammation in response to injury.

IL-6 regulates adipose deposition and homeostasis in lymphedema

Lymphedema (LE) is a morbid disease characterized by chronic limb swelling and adipose deposition. Although it is clear that lymphatic injury is necessary for this pathology, the mechanisms that underlie lymphedema remain unknown. IL-6 is a known regulator of adipose homeostasis in obesity and has been shown to be increased in primary and secondary models of lymphedema. Therefore, the purpose of this study was to determine the role of IL-6 in adipose deposition in lymphedema. The expression of IL-6 was analyzed in clinical tissue specimens and serum from patients with or without LE, as well as in two mouse models of lymphatic injury. In addition, we analyzed IL-6 expression/adipose deposition in mice deficient in CD4(+) cells (CD4KO) or IL-6 expression (IL-6KO) or mice treated with a small molecule inhibitor of IL-6 or CD4 depleting antibodies to determine how IL-6 expression is regulated and the effect of changes in IL-6 expression on adipose deposition after lymphatic injury. Patients with LE and mice treated with lymphatic excision of the tail had significantly elevated tissue and serum expression of IL-6 and its downstream mediator. The expression of IL-6 was associated with adipose deposition and CD4(+) inflammation and was markedly decreased in CD4KO mice. Loss of IL-6 function resulted in significantly increased adipose deposition after tail lymphatic injury. Our findings suggest that IL-6 is increased as a result of adipose deposition and CD4(+) cell inflammation in lymphedema. In addition, our study suggests that IL-6 expression in lymphedema acts to limit adipose accumulation.

The lymphatics and the inflammatory response: lessons learned from human lymphedema

In lymphedema, there is a profound predisposition to infection with bacterial pathogens. It therefore seems appropriate to reconsider our unique functional definition of the lymphatic structures within a circulatory construct. While the lymphatics unquestionably fulfill a vital circulatory function, it seems more appropriate to view this complex network, comprised both of endothelial-lined vessels and of lymphoid tissue, as the nexus between the circulatory and immune systems. Viewed in this fashion, it becomes evident that the complex biology of regional lymphatic disruption is a manifestation of the interplay between these two vital bodily functions. Experimental lymph stasis in murine model has been utilized to effectively demonstrate the pathological attributes of human lymphedema, namely, inflammation, fat deposition, and fibrosis. Large-scale transcriptional corroborates the role of inflammatory mechanisms. The murine studies have set the stage for subsequent translational investigation of human lymphedema. Many of the gene expression pathways invoked by lymphedema are relevant to the inflammatory response and have provided a pragmatic approach to the successful identification of potentially relevant circulating biomarkers for human lymphedema.

Molecular analysis and differentiation capacity of adipose-derived stem cells from lymphedema tissue

BACKGROUND

Many breast cancer patients are plagued by the disabling complication of upper limb lymphedema after axillary surgery. Conservative treatments using massage and compression therapy do not offer a lasting relief, as they fail to address the chronic transformation of edema into excess adipose tissue. Liposuction to address the adipose nature of the lymphedema has provided an opportunity for a detailed analysis of the stromal fraction of lymphedema-associated fat to clarify the molecular mechanisms for this adipogenic transformation.

METHODS

Adipose-derived stem cells were harvested from human lipoaspirate of the upper extremity from age-matched patients with lymphedema (n = 3) or subcutaneous adipose tissue from control patients undergoing cosmetic procedures (n = 3). Immediately after harvest, adipose-derived stem cells were analyzed using single-cell transcriptional profiling techniques. Osteogenic, adipogenic, and vasculogenic gene expression and differentiation were assessed by quantitative real-time polymerase chain reaction and standard in vitro differentiation assays.

RESULTS

Differential transcriptional clusters of adipose-derived stem cells were found between lymphedema and subcutaneous fat. Interestingly, lymphedema-associated stem cells had a much higher adipogenic gene expression and enhanced ability to undergo adipogenic differentiation. Conversely, they had lower vasculogenic gene expression and diminished capability to form tubules in vitro, whereas the osteogenic differentiation capacity was not significantly altered.

CONCLUSIONS

Adipose-derived stem cells from extremities affected by lymphedema appear to exhibit transcriptional profiles similar to those of abdominal adipose-derived stem cells; however, their adipogenic differentiation potential is strongly increased and their vasculogenic capacity is compromised. These results suggest that the underlying pathophysiology of lymphedema drives adipose-derived stem cells toward adipogenic differentiation.

Prospective transcriptomic pathway analysis of human lymphatic vascular insufficiency: identification and validation of a circulating biomarker panel

BACKGROUND

In our previous transcriptional profiling of a murine model, we have identified a remarkably small number of specific pathways with altered expression in lymphedema. In this investigation, we utilized microarray-based transcriptomics of human skin for an unbiased a priori prospective candidate identification, with subsequent validation of these candidates through direct serum assay. The resulting multi-analyte biomarker panel sensitively should sensitively discriminate human lymphedema subjects from normal individuals.

METHODS AND FINDINGS

We enrolled 63 lymphedema subjects and 27 normals in our attempt to discover protein analytes that can distinguish diseased individuals from controls. To minimize technical and biologically irrelevant variation, we first identified potential candidates by performing transcriptional microarray analysis on paired diseased and normal skin specimens sampled from the same individuals. We focused our attention on genes with corresponding protein products that are secreted and took these candidates forward to a protein multiplex assay applied to diseased and normal subjects. We developed a logistic regression-based model on an eventual group of six proteins and validated our system on a separate cohort of study subjects. The area under the receiver operating characteristic curve was calculated to be 0.87 (95% CI : 0.75 to 0.97).

CONCLUSIONS

We have developed an accurate bioassay utilizing proteins representing four central pathogenetic modalities of the disease: lymphangiogenesis, inflammation, fibrosis, and lipid metabolism, suggesting that these proteins are directly related to the pathogenesis of the tissue pathology in lymphatic vascular insufficiency. Further studies are warranted to determine whether this newly-identified biomarker panel will possess utility as an instrument for in vitro diagnosis of early and latent disease; the ultimate applicability to risk stratification, quantitation of disease burden, and response to therapy can easily be envisioned.