Lymphatic Biology and the Microcirculation: Past, Present and Future

Is there enhanced lymphatic function in upper body trained females?

BACKGROUND

Chronic physical activity results in adaptations in many aspects of human physiology, while specific training can directly influence structural changes. It remains unknown if habitual exercise influences upper extremity lymphatic function in females; thus, the purpose of this cross-sectional study was to compare different exercise stresses on lymphatic function in ten upper body trained females with ten untrained females.

METHODS AND RESULTS

Participants underwent a maximal upper body aerobic test on an arm crank ergometer before undergoing three randomly assigned lymphatic stress tests. Lymphoscintigraphy was used to quantify lymphatic function. (99m)Tc-antimony colloid was injected into the third web space of each hand, followed by 1 min spot views taken with a gamma-radiation camera. The maximal stress test required individuals to repeat their initial maximal exercise test. The subjects were then imaged every 10 min until 60 min were reached. The submaximal stress test involved arm cranking for 2.5 min at 0.6 W x kg(-1), followed by 2.5 min of rest, repeated for 60 min. The final stress test was a 60 min seated resting session. The clearance rate (CR) and axillary uptake (AX) were determined. Only AX post maximal exercise was significantly different between trained and untrained, p=0.009. All other measures of lymphatic function between groups were similar.

CONCLUSION

This study demonstrates no significant difference in lymphatic function between upper body trained and untrained females.

Calcium sensitivity and cooperativity of permeabilized rat mesenteric lymphatics

Lymphatic muscle contraction is critical for the centripetal movement of lymph that regulates fluid balance, protein homeostasis, lipid absorption, and immune function. We have demonstrated that lymphatic muscle has both smooth and striated muscle contractile elements; however, the basic contractile properties of this tissue remain poorly defined. We hypothesized that contractile characteristics of lymphatic myofilaments would be different from vascular smooth muscle myofilaments. To test this hypothesis, -log[Ca(2+)] (pCa)-tension relationship was determined for alpha-toxin permeabilized mesenteric lymphatics, arteries, and veins. The Ca(2+) sensitivity (pCa(50)) of mesenteric lymphatics was significantly lower compared with arteries (6.16 +/- 0.05 vs. 6.44 +/- 0.02; P < 0.05), whereas there was no difference in pCa(50) between lymphatics and veins (6.16 +/- 0.05 vs. 6.00 +/- 0.10; not significant). The Hill coefficient for alpha-toxin-permeabilized lymphatics was not significantly different from arteries but was significantly greater than that of the veins (1.98 +/- 0.19 vs. 1.21 +/- 0.18; P < 0.05). In addition, the maximal tension and pCa(50) values were significantly greater in alpha-toxin-permeabilized lymphatics compared with beta-escin-permeabilized lymphatics (0.27 +/- 0.03 vs. 0.15 +/- 0.01 and 6.16 +/- 0.05 vs. 5.86 +/- 0.06 mN/mm, respectively; P < 0.05), whereas the Hill coefficient was significantly greater in beta-escin-permeabilized lymphatics. Western blot analyses revealed that CPI-17 levels were significantly decreased by about 50% in beta-escin-permeabilized lymphatics, compared with controls, whereas no change in the level of calmodulin was detected. Our data constitute the first description of the pCa-tension relationship in permeabilized lymphatic muscle. It suggests that differences in myofilament Ca(2+) sensitivity and cooperativity among lymphatic muscle and vascular smooth muscles contribute to the functional differences that exist between these tissues.

Upper extremity lymphatic function at rest and during exercise in breast cancer survivors with and without lymphedema compared with healthy controls

Lymphoscintigraphy was used to measure lymphatic function at rest and during exercise in breast cancer survivors with lymphedema (BCRL, n = 10), breast cancer survivors (BC, n = 10), and controls (Cont, n = 10). After injection of 99mTc-antimony colloid to the hands, subjects rested or performed 12 repeated sets of arm cranking for 2.5 min at 0.6 W/kg followed by 2.5 min of rest. One-minute spot views were taken with a gamma-radiation camera immediately postinjection and every 10 min over 60 min to calculate clearance rate. As well, an upper body scan was taken at 65 min postinjection to measure radiopharmaceutical uptake in the axilla (Ax) and forearm (Fore). All groups displayed similar increases in clearance rate with exercise ( P = 0.000). Ax significantly increased with exercise in Cont only [Cont: (mean ± SD) 4.9 ± 2.6 vs. 7.9 ± 4.2%, P = 0.000; BCRL: 1.4 ± 1.2 vs. 1.7 ± 2.1%, P = 0.531; BC: 3.9 ± 3.4 vs. 5.2 ± 3.2%, P = 0.130], whereas Fore, indicating dermal backflow, significantly increased in BCRL only (BCRL: 2.4 ± 0.87 vs. 4.4 ± 2.0%, P = 0.004; BC: 1.1 ± 0.25 vs. 1.1 ± 0.31%, P = 0.784; Cont: 0.93 ± 0.26 vs. 1.0 ± 0.20%, P = 0.296). The results indicate that, in women with BCRL, exercise causes radiopharmaceuticals to clear from the hand at the same rate as BC and Cont, but, instead of reaching the axilla, a greater amount of activity gets trapped in the dermis of the forearm. BC, meanwhile, have similar lymphatic function as Cont; however, there is a highly variable response that may suggest that some BC subjects may be at risk for developing lymphedema.

Schlemm??s Canal Endothelia, Lymphatic, or Blood Vasculature?

In the human eye, the final barrier for aqueous humor to cross before returning to systemic circulation is the inner wall of Schlemm's canal. Unfortunately, the specific contribution of the inner wall to total outflow resistance in the conventional pathway is unknown in both normal and glaucomatous eyes. To better understand inner wall physiology, we contrasted it with 2 specialized continuous endothelia, initial lymphatic, and blood capillary endothelia. Specifically, we compare their developmental origin, morphology, junctional complexes, microenvironment, and physiologic responses to different biomechanical factors. Our evaluation concludes that the inner wall of Schlemm's canal is unique, sharing extraordinary characteristics with both types of specialized endothelia in addition to having distinctive features of its own.

Imaging of the lymphatic system: new horizons

The lymphatic system is a complex network of lymph vessels, lymphatic organs and lymph nodes. Traditionally, imaging of the lymphatic system has been based on conventional imaging methods like computed tomography (CT) and magnetic resonance imaging (MRI), whereby enlargement of lymph nodes is considered the primary diagnostic criterion for disease. This is particularly true in oncology, where nodal enlargement can be indicative of nodal metastases or lymphoma. CT and MRI on their own are, however, anatomical imaging methods. Newer imaging methods such as positron emission tomography (PET), dynamic contrast-enhanced MRI (DCE-MRI) and color Doppler ultrasound (CDUS) provide a functional assessment of node status. None of these techniques is capable of detecting flow within the lymphatics and, thus, several intra-lymphatic imaging methods have been developed. Direct lymphangiography is an all-but-extinct method of visualizing the lymphatic drainage from an extremity using oil-based iodine contrast agents. More recently, interstitially injected intra-lymphatic imaging, such as lymphoscintigraphy, has been used for lymphedema assessment and sentinel node detection. Nevertheless, radionuclide-based imaging has the disadvantage of poor resolution. This has lead to the development of novel systemic and interstitial imaging techniques which are minimally invasive and have the potential to provide both structural and functional information; this is a particular advantage for cancer imaging, where anatomical depiction alone often provides insufficient information. At present the respective role each modality plays remains to be determined. Indeed, multi-modal imaging may be more appropriate for certain lymphatic disorders. The field of lymphatic imaging is ever evolving, and technological advances, combined with the development of new contrast agents, continue to improve diagnostic accuracy.

Basement membrane protein distribution in LYVE-1-immunoreactive lymphatic vessels of normal tissues and ovarian carcinomas

The endothelial cells of blood vessels assemble basement membranes that play a role in vessel formation, maintenance and function, and in the migration of inflammatory cells. However, little is known about the distribution of basement membrane constituents in lymphatic vessels. We studied the distribution of basement membrane proteins in lymphatic vessels of normal human skin, digestive tract, ovary and, as an example of tumours with abundant lymphatics, ovarian carcinomas. Basement membrane proteins were localized by immunohistochemistry with monoclonal antibodies, whereas lymphatic capillaries were detected with antibodies to the lymphatic vessel endothelial hyaluronan receptor-1, LYVE-1. In skin and ovary, fibrillar immunoreactivity for the laminin alpha4, beta1, beta2 and gamma1 chains, type IV and XVIII collagens and nidogen-1 was found in the basement membrane region of the lymphatic endothelium, whereas also heterogeneous reactivity for the laminin alpha5 chain was detected in the digestive tract. Among ovarian carcinomas, intratumoural lymphatic vessels were found especially in endometrioid carcinomas. In addition to the laminin alpha4, beta1, beta2 and gamma1 chains, type IV and XVIII collagens and nidogen-1, carcinoma lymphatics showed immunoreactivity for the laminin alpha5 chain and Lutheran glycoprotein, a receptor for the laminin alpha5 chain. In normal lymphatic capillaries, the presence of primarily alpha4 chain laminins may therefore compromise the formation of endothelial basement membrane, as these truncated laminins lack one of the three arms required for efficient network assembly. The localization of basement membrane proteins adjacent to lymphatic endothelia suggests a role for these proteins in lymphatic vessels. The distribution of the laminin alpha5 chain and Lutheran glycoprotein proposes a difference between normal and carcinoma lymphatic capillaries.

Production of two novel monoclonal antibodies that distinguish mouse lymphatic and blood vascular endothelial cells

We produced two novel rat monoclonal antibodies (LA102 and LA5) to identify mouse lymphatic vessels and blood vessels, respectively. We characterized the two antibodies as to the morphological and functional specificities of endothelial cells of both types of vessels. The antibodies were produced by a rapid differential immunization of DA rats with collagenase- and neuraminidase-treated mouse lymphangioma tissues. LA102 specifically reacted with mouse lymphatic vessels except the thoracic duct and the marginal sinus of lymph nodes, but not with any blood vessels. In contrast, LA5 reacted with most mouse blood vessels with a few exceptions, but not with lymphatics. LA102 recognized a protein of 25-27 kDa, whereas LA5 recognized a molecule of 12-13 kDa. Neither antibody recognized any currently identified lymphatic or vascular endothelial cell antigens. Immunoelectron microscopy revealed that the antigens recognized by LA102 and LA5 were localized on both luminal and abluminal endothelial cell membranes of each vessel type. Interestingly, LA102 immunoreactivity was strongly expressed on pinocytic or transport vesicle membrane in the cytoplasm of lymphatic endothelium. Besides endothelial cells, both antibodies also recognized some types of lymphoid cells. Since, the LA102 antigen molecule is expressed on some lymphoid cells, it may play important roles in the migration of lymphoid cells and in some transport mechanisms through lymphatic endothelial cells.

Microarray Analysis of VEGF-C Responsive Genes in Human Lymphatic Endothelial Cells

Vascular endothelial growth factor-C (VEGF-C) is considered one of the most important factors influencing lymphatic endothelial cell biology. The goal of this work was to characterize the gene expression response by lymphatic endothelial cells (LECs) to VEGF-C. Primary cultures of human microvascular LECs were exposed to 100 ng/mL VEGF-C for 30 minutes and 6 hours, and their lysates were evaluated by microarray analysis to determine changes in mRNA expression induced by VEGF-C. Characteristic of a response to a growth factor stimulus, the largest number of differentially expressed genes were transcription factors and cell cycle related. A number of genes known to be important in angiogenesis, tumorigenesis and tumor invasion, and the transport of proteins, solutes, and lipids were also affected. Interestingly, a number of genes related to lipid metabolism as well as neurogenesis and neurodegeneration were also responsive to VEGF-C stimulation. Further analysis of these genes may not only provide insight into the molecular mechanisms underlying lymphangiogenesis and associated pathogenesis, but may also identify other important roles of VEGF-C.