Increased lymphangiogenesis in joints of mice with inflammatory arthritis

Histological and biochemical changes in lymphatic vessels after skeletal muscle injury induced by lengthening contraction in male mice

Lymphatic vessels are actively involved in the recovery process of inflamed tissues. However, the changes in intramuscular lymphatic vessels during inflammation caused by skeletal muscle injury remain unclear. Therefore, the purpose of this study was to clarify the changes in lymphatic vessels after skeletal muscle injury. The left tibialis anterior muscles of male mice were subjected to lengthening contractions (LC) for inducing skeletal muscle injury, and samples were collected on Days 2, 4, and 7 for examining changes in both the skeletal muscles and intramuscular lymphatic vessels. With hematoxylin-eosin staining, the inflammatory response was observed in myofibers on Days 2 and 4 after LC, whereas regeneration of myofibers was found on Day 7 after LC. The number and area of intramuscular lymphatic vessels analyzed by immunohistochemical staining with an antibody against lymphatic vessel endothelial hyaluronan receptor 1 were significantly increased only on Day 4 after LC. Based on the abovementioned results, intramuscular lymphatic vessels undergo morphological changes such as increase under the state of muscle inflammation. This study demonstrated that the morphology of intramuscular lymphatic vessels undergoes significant changes during the initial recovery phase following skeletal muscle injury.

Epigenetic targets to enhance antitumor immune response through the induction of tertiary lymphoid structures

Tertiary lymphoid structures (TLS) are ectopic lymphoid aggregates found in sites of chronic inflammation such as tumors and autoimmune diseases. The discovery that TLS formation at tumor sites correlated with good patient prognosis has triggered extensive research into various techniques to induce their formation at the tumor microenvironment (TME). One strategy is the exogenous induction of specific cytokines and chemokine expression in murine models. However, applying such systemic chemokine expression can result in significant toxicity and damage to healthy tissues. Also, the TLS formed from exogenous chemokine induction is heterogeneous and different from the ones associated with favorable prognosis. Therefore, there is a need to optimize additional approaches like immune cell engineering with lentiviral transduction to improve the TLS formation in vivo. Similarly, the genetic and epigenetic regulation of the different phases of TLS neogenesis are still unknown. Understanding these molecular regulations could help identify novel targets to induce tissue-specific TLS in the TME. This review offers a unique insight into the molecular checkpoints of the different stages and mechanisms involved in TLS formation. This review also highlights potential epigenetic targets to induce TLS neogenesis. The review further explores epigenetic therapies (epi-therapy) and ongoing clinical trials using epi-therapy in cancers. In addition, it builds upon the current knowledge of tools to generate TLS and TLS phenotyping biomarkers with predictive and prognostic clinical potential.

Lymphatic vessels: roles and potential therapeutic intervention in rheumatoid arthritis and osteoarthritis

Lymphatic vessel networks are a main part of the vertebrate cardiovascular system, which participate in various physiological and pathological processes via regulation of fluid transport and immunosurveillance. Targeting lymphatic vessels has become a potent strategy for treating various human diseases. The presence of varying degrees of inflammation in joints of rheumatoid arthritis (RA) and osteoarthritis (OA), characterized by heightened infiltration of inflammatory cells, increased levels of inflammatory factors, and activation of inflammatory signaling pathways, significantly contributes to the disruption of cartilage and bone homeostasis in arthritic conditions. Increasing evidence has demonstrated the pivotal role of lymphatic vessels in maintaining joint homeostasis, with their pathological alterations closely associated with the initiation and progression of inflammatory joint diseases. In this review, we provide a comprehensive overview of the evolving knowledge regarding the structural and functional aspects of lymphatic vessels in the pathogenesis of RA and OA. In addition, we summarized the potential regulatory mechanisms underlying the modulation of lymphatic function in maintaining joint homeostasis during inflammatory conditions, and further discuss the distinctions between RA and OA. Moreover, we describe therapeutic strategies for inflammatory arthritis based on lymphatic vessels, including the promotion of lymphangiogenesis, restoration of proper lymphatic vessel function through anti-inflammatory approaches, enhancement of lymphatic contractility and drainage, and alleviation of congestion within the lymphatic system through the elimination of inflammatory cells. At last, we envisage potential research perspectives and strategies to target lymphatic vessels in treating these inflammatory joint diseases.

Tailoring biomaterials for monitoring and evoking tertiary lymphoid structures

Despite the remarkable clinical success of immune checkpoint blockade (ICB) in the treatment of cancer, the response rate to ICB therapy remains suboptimal. Recent studies have strongly demonstrated that intratumoral tertiary lymphoid structures (TLSs) are associated with a good prognosis and a successful clinical response to immunotherapy. However, there is still a shortage of efficient and wieldy approaches to image and induce intratumoral TLSs in vivo. Biomaterials have made great strides in overcoming the deficiencies of conventional diagnosis and therapies for cancer, and antitumor therapy has also benefited from biomaterial-based drug delivery models. In this review, we summarize the reported methods for TLS imaging and induction based on biomaterials and provide potential strategies that can further enhance the effectiveness of imaging and stimulating intratumoral TLSs to predict and promote the response rates of ICB therapies for patients. STATEMENT OF SIGNIFICANCE: In this review, we focused on the promising of biomaterials for imaging and induction of TLSs. We reviewed the applications of biomaterials in molecular imaging and immunotherapy, identified the biomaterials that may be suitable for TLS imaging and induction, and provided outlooks for further research. Accurate imaging and effective induction of TLSs are of great significance for understanding the mechanism and clinical application. We highlighted the need for multidisciplinary coordination and cooperation in this field, and proposed the possible future direction of noninvasive imaging and artificial induction of TLSs based on biomaterials. We believe that it can facilitate collaboration and galvanize a broader effort.

Biomechanical control of lymphatic vessel physiology and functions

The ever-growing research on lymphatic biology has clearly identified lymphatic vessels as key players that maintain human health through their functional roles in tissue fluid homeostasis, immunosurveillance, lipid metabolism and inflammation. It is therefore not surprising that the list of human diseases associated with lymphatic malfunctions has grown larger, including issues beyond lymphedema, a pathology traditionally associated with lymphatic drainage insufficiency. Thus, the discovery of factors and pathways that can promote optimal lymphatic functions may offer new therapeutic options. Accumulating evidence indicates that aside from biochemical factors, biomechanical signals also regulate lymphatic vessel expansion and functions postnatally. Here, we review how mechanical forces induced by fluid shear stress affect the behavior and functions of lymphatic vessels and the mechanisms lymphatic vessels employ to sense and transduce these mechanical cues into biological signals.

Maladaptive lymphangiogenesis is associated with synovial iron accumulation and delayed clearance in factor VIII-deficient mice after induced hemarthrosis

BACKGROUND

Mechanisms of iron clearance from hemophilic joints are unknown.

OBJECTIVES

To better understand mechanisms of iron clearance following joint bleeding in a mouse model of hemophilia.

METHODS

Hemarthrosis was induced by subpatellar puncture in factor VIII (FVIII)-deficient (FVII-/-) mice, +/- periprocedural recombinant human FVIII, and hypocoagulable (HypoBALB/c) mice. HypoBALB/c mice experienced transient FVIII deficiency (anti-FVIII antibody) at the time of injury combined with warfarin-induced hypocoagulability. Synovial tissue was harvested weekly up to 6 weeks after injury for histological analysis, ferric iron and macrophage accumulation (CD68), blood and lymphatic vessel remodeling (αSMA; LYVE1). Synovial RNA sequencing was performed for FVIII-/- mice at days 0, 3, and 14 after injury to quantify expression changes of iron regulators and lymphatic markers.

RESULTS

Bleed volumes were similar in FVIII-/- and HypoBALB/c mice. However, pronounced and prolonged synovial iron accumulation colocalizing with macrophages and impaired lymphangiogenesis were detected only in FVIII-/- mice and were prevented by periprocedural FVIII. Gene expression changes involved in iron handling (some genes with dual roles in inflammation) and lymphatic markers supported proinflammatory milieu with iron retention and disturbed lymphangiogenesis.

CONCLUSION

Accumulation and delayed clearance of iron-laden macrophages were associated with defective lymphangiogenesis after hemarthrosis in FVIII-/- mice. The absence of such findings in HypoBALB/c mice suggests that intact lymphatics are required for removal of iron-laden macrophages and that these processes depend on FVIII availability. Studies to elucidate the biological mechanisms of disturbed lymphangiogenesis in hemophilia appear critical to develop new therapeutic targets.

Targeting Synovial Lymphatic Function as a Novel Therapeutic Intervention for Age-Related Osteoarthritis in Mice

OBJECTIVE

The synovial lymphatic system (SLS) removes catabolic factors from the joint. Vascular endothelial growth factor C (VEGF-C) and its receptor, VEGFR-3, are crucial for lymphangiogenesis. However, their involvement in age-related osteoarthritis (OA) is unknown. This study was undertaken to determine whether the SLS and the VEGF-C/VEGFR-3 pathway contribute to the development and progression of age-related OA, using a murine model of naturally occurring joint disease.

METHODS

SLS function was assessed in the knees of young (3-month-old) and aged (19-24-month-old) male and female C57BL/6J mice via a newly established in vivo IVIS-dextran imaging approach, which, in addition to histology, was used to assess the effects of VEGF-C treatment on SLS function and OA pathology in aged mice. RNA-sequencing of synovial tissue was performed to explore molecular mechanisms of the disease in the mouse knee joints.

RESULTS

Results showed that aged mice had impaired SLS function, including decreases in joint clearance (mean T1/2 of signal intensity clearance, 2.8 hours in aged mice versus 0.5 hours in young mice; P < 0.0001), synovial influx (mean ± SD 1.7 ± 0.8% in aged mice versus 4.1 ± 1.9% in young mice; P = 0.0004), and lymph node draining capacity (mean ± SD epifluorescence total radiant intensity ([photons/second]/[μW/cm2 ]) 1.4 ± 0.8 in aged mice versus 3.7 ± 1.2 in young mice; P < 0.0001). RNA-sequencing of the synovial tissue showed that Vegf-c and Vegfr3 signaling genes were decreased in the synovium of aged mice. VEGF-C treatment resulted in improvements in SLS function in aged mice, including increased percentage of signal intensity joint clearance (mean ± SD 63 ± 9% in VEGF-C-treated aged mice versus 52 ± 15% in vehicle-treated aged mice; P = 0.012), increased total articular cartilage cross-sectional area (mean ± SD 0.38 ± 0.07 mm2 in VEGF-C-treated aged mice versus 0.26 ± 0.07 mm2 in vehicle-treated aged mice; P < 0.0001), and decreased percentage of matrix metallopeptidase 13-positive staining area within total synovial area in 22-month-old VEGF-C-treated mice versus 22-month-old vehicle-treated mice (mean ± SD decrease 7 ± 2% versus 4 ± 1%; P = 0.0004).

CONCLUSION

SLS function is reduced in the knee joints of aged mice due to decreased VEGF-C/VEGFR-3 signaling. VEGF-C treatment attenuates OA joint damage and improves synovial lymphatic drainage in aged mice. The SLS and VEGF-C/VEGFR-3 signaling represent novel physiopathologic mechanisms that could potentially be used as therapeutic targets for age-related OA.

Engineering approaches to investigate the roles of lymphatics vessels in rheumatoid arthritis

Rheumatoid arthritis (RA) is one of the most common chronic inflammatory joint disorders. While our understanding of the autoimmune processes that lead to synovial degradation has improved, a majority of patients are still resistant to current treatments and require new therapeutics. An understudied and promising area for therapy involves the roles of lymphatic vessels (LVs) in RA progression, which has been observed to have a significant effect on mediating chronic inflammation. RA disease progression has been shown to correlate with dramatic changes in LV structure and interstitial fluid drainage, manifesting in the retention of distinct immune cell phenotypes within the synovium. Advances in dynamic imaging technologies have demonstrated that LVs in RA undergo an initial expansion phase of increased LVs and abnormal contractions followed by a collapsed phase of reduced lymphatic function and immune cell clearance in vivo. However, current animal models of RA fail to decouple biological and biophysical factors that might be responsible for this lymphatic dysfunction in RA, and a few attempted in vitro models of the synovium in RA have not yet included the contributions from the LVs. Various methods of replicating LVs in vitro have been developed to study lymphatic biology, but these have yet not been integrated into the RA context. This review discusses the roles of LVs in RA and the current engineering approaches to improve our understanding of lymphatic pathophysiology in RA.

Intra-articular Injection of a B Cell Depletion Antibody Enhances Local Exposure to the Joint-Draining Lymph Node in Mice with Collagen-Induced Arthritis

Changes to the number, type, and function of immune cells within the joint-draining lymphatics is a major contributor to the progression of inflammatory arthritis. In particular, there is a significant expansion in pathogenic B cells in the joint-draining lymph node (jdLN). These B cells appear to clog the lymphatic sinuses in the lymph node, inhibit lymph flow, and therefore, reduce the clearance of inflammatory fluid and cells from the joint. Taken together, there is potential to treat inflammatory arthritis more effectively, as well as reduce off-target side effects, with localized delivery of B-cell depleting therapies to the jdLNs. We recently reported that joint-draining lymphatic exposure of biologic disease-modifying anti-rheumatic drugs (DMARDs), including the B cell depletion antibody rituximab, is increased in healthy rats following intra-articular (IA) compared to subcutaneous (SC) or intravenous (IV) administration. This suggests that IA administration of B cell depleting antibodies may increase delivery to target cells in the jdLN and increase the effectiveness of B cell depletion compared to standard SC or IV administration. However, whether enhanced local delivery of DMARDs to the jdLN is also achieved after IA injection in the setting of inflammatory arthritis, where there is inflammation in the joint and jdLN B cell expansion is unknown. We, therefore, assessed the lymph node distribution, absorption and plasma pharmacokinetics, and B cell depletion at different sites after IA, SC, or IV administration of a fluorescently labeled mouse anti-CD20 B cell depleting antibody (Cy5-αCD20) in healthy mice compared to mice with collagen-induced arthritis (CIA). The absorption and plasma pharmacokinetics of Cy5-αCD20 appeared unaltered in mice with CIA whereas distribution of Cy5-αCD20 to the jdLNs was generally increased in mice with CIA, regardless of the route of administration. However, IA administration led to greater and more specific exposure to the jdLNs. Consistent with increased Cy5-αCD20 in the jdLNs of CIA compared to healthy mice, there was a greater reduction in jdLN weight and a trend toward greater jdLN B cell depletion at 24 h compared to 4 h after IA compared to SC and IV administration. Taken together, this data supports the potential to improve local efficacy of B cell depletion therapies through a jdLN-directed approach which will enable a reduction in dose and systemic toxicities.

Tertiary lymphoid structures are critical for cancer prognosis and therapeutic response

Tertiary lymphoid structures (TLSs) are ectopic lymphocyte aggregates that form at sites of chronic inflammation, including cancers, in non-lymphoid tissues. Although the formation of TLSs is similar to that of secondary lymphoid organs, the pathogenic factors leading to TLS formation in cancerous tissues and the mechanisms underlying the role of these structures in the intra-tumoral adaptive antitumor immune response are not fully understood. The presence of TLSs may impact patient prognosis and treatment outcomes. This review examines the current understanding of TLSs in cancers, including their composition and formation as well as their potential to predict prognosis and therapeutic efficacy. We also summarize strategies to induce TLS formation for cancer treatment.

Teriparatide prevented synovial inflammation and cartilage destruction in mice with DMM

AIM

Emerging data have demonstrated that low-grade inflammation in osteoarthritis, a long-held degenerative disease. The inflamed synovium produces various cytokines that induce cartilage destruction and joint pain. A previous study showed that teriparatide, an FDA approved anti-osteoporotic drug, may enhance cartilage repair. Our study focuses on its role in OA synovitis.

MATERIALS AND METHODS

Primary mouse articular chondrocytes were used to determine the most potent cytokines involved in OA inflammation and cartilage destruction. A destabilization of the medial meniscus mouse model was established to investigate the effect of teriparatide in OA, particularly, on synovial inflammation and cartilage degradation.

RESULTS

In vitro experiments showed that TNF-α was the most potent inducer of cartilage matrix-degrading enzymes, and that teriparatide antagonized the TNF-α of effect. Consistently, articular cartilage samples from TNF-α transgenic mice contained more MMP-13 positive chondrocytes than those from wild type mice. In addition, more type II collagen was cleaved in human OA cartilage than in normal cartilage samples.

CONCLUSIONS

Teriparatide can prevent synovitis and cartilage degradation by suppressing TNF-α mediated MMP-13 overexpression. Together with its chondroregenerative capability, teriparatide may be the first effective disease modifying osteoarthritis drug.

Genetically inducing renal lymphangiogenesis attenuates hypertension in mice

BACKGROUND

Hypertension (HTN) is associated with renal proinflammatory immune cell infiltration and increased sodium retention. We reported previously that renal lymphatic vessels, which are responsible for trafficking immune cells from the interstitial space to draining lymph nodes, increase in density under hypertensive conditions. We also demonstrated that augmenting renal lymphatic density can prevent HTN in mice. Whether renal lymphangiogenesis can treat HTN in mice is unknown. We hypothesized that genetically inducing renal lymphangiogenesis after the establishment of HTN would attenuate HTN in male and female mice from three different HTN models.

METHODS

Mice with inducible kidney-specific overexpression of VEGF-D (KidVD) experience renal lymphangiogenesis upon doxycycline administration. HTN was induced in KidVD+ and KidVD- mice by subcutaneous release of angiotensin II, administration of the nitric oxide synthase inhibitor L-NAME, or consumption of a 4% salt diet following a L-NAME priming and washout period. After a week of HTN stimuli treatment, doxycycline was introduced. Systolic blood pressure (SBP) readings were taken weekly. Kidney function was determined from urine and serum measures. Kidneys were processed for RT-qPCR, flow cytometry, and imaging.

RESULTS

Mice that underwent renal-specific lymphangiogenesis had significantly decreased SBP and renal proinflammatory immune cells. Additionally, renal lymphangiogenesis was associated with a decrease in sodium transporter expression and increased fractional excretion of sodium, indicating improved sodium handling efficiency.

CONCLUSIONS

These findings demonstrate that augmenting renal lymphangiogenesis can treat HTN in male and female mice by improving renal immune cell trafficking and sodium handling.

Osteopathy in Complex Lymphatic Anomalies

Complex Lymphatic Anomalies (CLA) are lymphatic malformations with idiopathic bone and soft tissue involvement. The extent of the abnormal lymphatic presentation and boney invasion varies between subtypes of CLA. The etiology of these diseases has proven to be extremely elusive due to their rarity and irregular progression. In this review, we compiled literature on each of the four primary CLA subtypes and discuss their clinical presentation, lymphatic invasion, osseous profile, and regulatory pathways associated with abnormal bone loss caused by the lymphatic invasion. We highlight key proliferation and differentiation pathways shared between lymphatics and bone and how these systems may interact with each other to stimulate lymphangiogenesis and cause bone loss.

Tertiary lymphoid structures in cancer

Ectopic lymphoid aggregates, termed tertiary lymphoid structures (TLSs), are formed in numerous cancer types, and, with few exceptions, their presence is associated with superior prognosis and response to immunotherapy. In spite of their presumed importance, the triggers that lead to TLS formation in cancer tissue and the contribution of these structures to intratumoral immune responses remain incompletely understood. Here, we discuss the present knowledge on TLSs in cancer, focusing on (i) the drivers of TLS formation, (ii) the function and contribution of TLSs to the antitumor immune response, and (iii) the potential of TLSs as therapeutic targets in human cancers.

Ex vivo Demonstration of Functional Deficiencies in Popliteal Lymphatic Vessels From TNF-Transgenic Mice With Inflammatory Arthritis

Background: Recent studies demonstrated lymphangiogenesis and expansion of draining lymph nodes during chronic inflammatory arthritis, and lymphatic dysfunction associated with collapse of draining lymph nodes in rheumatoid arthritis (RA) patients and TNF-transgenic (TNF-Tg) mice experiencing arthritic flare. As the intrinsic differences between lymphatic vessels afferent to healthy, expanding, and collapsed draining lymph nodes are unknown, we characterized the ex vivo behavior of popliteal lymphatic vessels (PLVs) from WT and TNF-Tg mice. We also interrogated the mechanisms of lymphatic dysfunction through inhibition of nitric oxide synthase (NOS). Methods: Popliteal lymph nodes (PLNs) in TNF-Tg mice were phenotyped as Expanding or Collapsed by in vivo ultrasound and age-matched to WT littermate controls. The PLVs were harvested and cannulated for ex vivo functional analysis over a relatively wide range of hydrostatic pressures (0.5-10 cmH2O) to quantify the end diastolic diameter (EDD), tone, amplitude (AMP), ejection fraction (EF), contraction frequency (FREQ), and fractional pump flow (FPF) with or without NOS inhibitors Data were analyzed using repeated measures two-way ANOVA with Bonferroni's post hoc test. Results: Real time videos of the cannulated PLVs demonstrated the predicted phenotypes of robust vs. weak contractions of the WT vs. TNF-Tg PLV, respectively. Quantitative analyses confirmed that TNF-Tg PLVs had significantly decreased AMP, EF, and FPF vs. WT (p < 0.05). EF and FPF were recovered by NOS inhibition, while the reduction in AMP was NOS independent. No differences in EDD, tone, or FREQ were observed between WT and TNF-Tg PLVs, nor between Expanding vs. Collapsed PLVs. Conclusion: These findings support the concept that chronic inflammatory arthritis leads to NOS dependent and independent draining lymphatic vessel dysfunction that exacerbates disease, and may trigger arthritic flare due to decreased egress of inflammatory cells and soluble factors from affected joints.

Morphological and biochemical changes of lymphatic vessels in the soleus muscle of mice after hindlimb unloading

INTRODUCTION/AIMS

Lymphatic vessels are responsible for the removal of metabolic waste from body tissues. They also play a crucial role in skeletal muscle functioning thorough their high-energy metabolism. In this study we investigated whether disuse muscle atrophy induced by hindlimb unloading is associated with an alteration in the number of lymphatic vessels and differential expression of lymphangiogenic factors in the soleus muscle.

METHODS

Male C57BL/6 mice were subjected to tail suspension (TS) for 2 or 4 weeks to induce soleus muscle atrophy. After TS, lymphatic and blood capillaries in the soleus muscle were visualized and counted by double staining with LYVE-1 and CD31. The protein and mRNA levels of vascular endothelial growth factor (VEGF)-C, VEGF-D, and vascular endothelial growth factor receptor-3 were measured by Western blotting and real-time reverse transcript polymerase chain reaction, respectively.

RESULTS

TS for 2 weeks resulted in a significant decrease in the number of blood capillaries compared with controls. However, there was no significant change in the number of lymphatic capillaries. By contrast, TS for 4 weeks resulted in a significant decrease in the number of lymphatic and blood capillaries. We observed a significant decrease in the mRNA levels of VEGF-C and VEGF-D in mice subjected to TS for 4 weeks.

DISCUSSION

The decrease of intramuscular lymphatic vessels may a crucial role in the process of muscle atrophy.

Physiological models for in vivo imaging and targeting the lymphatic system: Nanoparticles and extracellular vesicles

Imaging of the lymphatic vasculature has gained great attention in various fields, not only because lymphatic vessels act as a key draining system in the body, but also for their implication in autoimmune diseases, organ transplant, inflammation and cancer. Thus, neolymphangiogenesis, or the generation of new lymphatics, is typically an early event in the development of multiple tumor types, particularly in aggressive ones such as malignant melanoma. Still, the understanding of how lymphatic endothelial cells get activated at distal (pre)metastatic niches and their impact on therapy is still unclear. Addressing these questions is of particular interest in the case of immune modulators, because endothelial cells may favor or halt inflammatory processes depending on the cellular context. Therefore, there is great interest in visualizing the lymphatic vasculature in vivo. Here, we review imaging tools and mouse models used to analyze the lymphatic vasculature during tumor progression. We also discuss therapeutic approaches based on nanomedicines to target the lymphatic system and the potential use of extracellular vesicles to track and target sentinel lymph nodes. Finally, we summarize main pre-clinical models developed to visualize the lymphatic vasculature in vivo, discussing their applications with a particular focus in metastatic melanoma.

The E3 ubiquitin ligase Itch limits the progression of post-traumatic osteoarthritis in mice by inhibiting macrophage polarization

OBJECTIVE

Osteoarthritis (OA) is characterized by articular cartilage loss, associated with synovial inflammation. We recently reported increased pro-inflammatory macrophages in murine post-traumatic OA (PTOA) joints, and blockade of the ubiquitin-proteasome system alleviates PTOA progression. However, the mechanisms whereby protein ubiquitination influences PTOA pathology are not well studied. We hypothesized that loss of the negative regulator of inflammation, E3 ligase Itch, in macrophages contributes to joint OA tissue damage by promoting pro-inflammatory polarization of macrophages.

METHODS

Mice deficient Itch in macrophages (MΔItch) were generated by crossing Itchfl/fl mice with LysM-Cre mice. PTOA surgery was performed on global Itch knockout, Itch-/-, mice and MΔItch mice. Joint tissue damage and synovial macrophages were examined. Itch-/- cells were treated with IL-1 and pro-inflammatory polarization was determined. Expression of Itch protein and mRNA in PTOA synovium were assessed at different time points post PTOA.

RESULTS

Similar to Itch-/- mice, MΔItch mice developed more severe joint damage than control mice following PTOA surgery (mean difference of OARSI score: 1.17 (95% CI 0.31-2.03) between MΔItch and Itchfl/fl mice), accompanied by increased the inflammatory macrophage infiltration in the synovium (mean difference of % F4/80 + CD86 + CD36-inflammatory macrophages: 14.81 (95% CI 8.90-20.73) between MΔItch and Itchfl/fl mice). Itch-/- macrophages exerted pro-inflammatory phenotype in response to IL-1β treatment. Itch protein, but not mRNA levels decreased during PTOA progression.

CONCLUSION

The negative regulator of inflammation, Itch, limits PTOA progression by inhibiting macrophage pro-inflammatory polarization. Itch protein degradation may contribute to PTOA pathology.

Effects of TNFα receptor TNF-Rp55- or TNF-Rp75- deficiency on corneal neovascularization and lymphangiogenesis in the mouse

Tumor necrosis factor (TNF)α is an inflammatory cytokine likely to be involved in the process of corneal inflammation and neovascularization. In the present study we evaluate the role of the two receptors, TNF-receptor (TNF-R)p55 and TNF-Rp75, in the mouse model of suture-induced corneal neovascularization and lymphangiogenesis. Corneal neovascularization and lymphangiogenesis were induced by three 11-0 intrastromal corneal sutures in wild-type (WT) C57BL/6J mice and TNF-Rp55-deficient (TNF-Rp55d) and TNF-Rp75-deficient (TNF-Rp75d) mice. The mRNA expression of VEGF-A, VEGF-C, Lyve-1 and TNFα and its receptors was quantified by qPCR. The area covered with blood- or lymphatic vessels, respectively, was analyzed by immunohistochemistry of corneal flatmounts. Expression and localization of TNFα and its receptors was assessed by immunohistochemistry of sagittal sections and Western Blot. Both receptors are expressed in the murine cornea and are not differentially regulated by the genetic alteration. Both TNF-Rp55d and TNF-Rp75d mice showed a decrease in vascularized area compared to wild-type mice 14 days after suture treatment. After 21 days there were no differences detectable between the groups. The number of VEGF-A-expressing macrophages did not differ when comparing WT to TNF-Rp55d and TNF-Rp75d. The mRNA expression of lymphangiogenic markers VEGF-C or LYVE-1 does not increase after suture in all 3 groups and lymphangiogenesis showed a delayed effect only for TNF-Rp75d. TNFα mRNA and protein expression increased after suture treatment but showed no difference between the three groups. In the suture-induced mouse model, TNFα and its ligands TNF-Rp55 and TNF-Rp75 do not play a significant role in the pathogenesis of neovascularisation and lymphangiogenesis.

Development and aging of the lymphatic vascular system

The lymphatic vasculature has a pivotal role in regulating body fluid homeostasis, immune surveillance and dietary fat absorption. The increasing number of in vitro and in vivo studies in the last decades has shed light on the processes of lymphatic vascular development and function. Here, we will discuss the current progress in lymphatic vascular biology such as the mechanisms of lymphangiogenesis, lymphatic vascular maturation and maintenance and the emerging mechanisms of lymphatic vascular aging.

Absence of lymphatic vessels in non-functioning bleb capsules of glaucoma drainage devices

PURPOSE

To evaluate the presence and appearance of blood and lymphatic vessels in non-functioning bleb capsules of glaucoma drainage devices (GDD).

MATERIALS AND METHODS

Non-functioning (n=14) GDD-bleb capsules of 12 patients were analyzed by immunohistochemistry for blood vessels (CD31, vascular endothelium), lymphatic vessels (lymphatic vessel endothelial hyaluronan receptor-1 [LYVE-1] and podoplanin) and macrophages (CD68).

RESULTS

CD31+++ blood vessels and CD68+ macrophages were detected in the outer layer of all specimens. LYVE-1 immunoreactivity was registered in single non-endothelial cells in 8 out of 14 (57%) bleb capsule specimens. Podoplanin-immunoreactivity was detected in all cases, located in cells and profiles of the collagen tissue network of the outer and/or the inner capsule layer. However, a colocalization of LYVE-1 and podoplanin as evidence for lymphatic vessels was not detected.

CONCLUSIONS

We demonstrate the presence of blood-vessels but absence of lymphatic vessels in non-functioning bleb capsules after GDD-implantation. While the absence of lymphatic vessels might indicate a possible reason for drainage device failure, this needs to be confirmed in upcoming studies, including animal experiments.

Comparative Analysis of the Occurrence and Role of CX3CL1 (Fractalkine) and Its Receptor CX3CR1 in Hemophilic Arthropathy and Osteoarthritis

Objective

Hemophilic arthropathy is characterized by recurrent bleeding episodes in patients with hemophilia leading to irreversible joint degeneration. The involvement of CX3CL1 (fractalkine) and its receptor CX3CR1 was observed in the pathogenesis of numerous arthritis-associated diseases. Taking this into account, we have presented a study investigating the role of the CX3CL1/CX3XR1 axis in the course of hemophilic arthropathy, including the CX3CL1-dependent expression of CD56⁺, CD68⁺, and CD31⁺ cells along with evaluation of articular cartilage and synovial membrane morphology.

Methods

The study was carried out using cases (n = 20) of end-stage hemophilic arthropathy with a severe type of hemophilia A and control cases (n = 20) diagnosed with osteoarthritis. The biofluids including blood serum and synovial fluid were obtained intraoperatively for the evaluation of CX3CL1 using the ELISA test. Tissue specimens including articular cartilage and synovial membrane were similarly collected during surgery and stained immunohistologically using selected antibodies including anti-CX3CR1, anti-CD56, anti-CD68, and anti-CD31. Additionally, the analysis included the assessment of articular cartilage, synovial membrane, and blood vessel morphology.

Results

In our study, we have documented increased average concentration of CX3CL1 in the blood serum of the study group (7.16 ± 0.53 ng/ml) compared to the control group (5.85 ± 0.70 ng/ml) without statistically significant difference in synovial fluid concentration at the same time. We have observed an increased macrophage presence with more marked proliferation and fibrosis of the synovial membrane in the study group. Remaining results such as expression of CX3CR1 presence of NK cells and larger surface area of blood vessels within the synovial membrane were noted also without statistical significance.

Conclusions

This study has demonstrated collective CX3CL1/CX3CR1 axis involvement in hemophilic arthropathy pathogenesis introducing new interesting diagnostics and a therapeutic target.

Effect of VEGFC on lymph flow and inflammation-induced alveolar bone loss

The lymphatic system plays a crucial role in the maintenance of tissue fluid homeostasis and the immunological response to inflammation. The effects of lymphatic drainage dysfunction on periodontitis have not been well studied. Here we show that lymphatic vessel endothelial receptor 1 (LYVE1)+ /podoplanin (PDPN)+ lymphatic vessels (LVs) are increased in the periodontal tissues, with accumulation close to the alveolar bone surface, in two murine periodontitis models: rheumatoid arthritis (RA)-associated periodontitis and ligature-induced periodontitis. Further, PDPN+ /alpha-smooth muscle actin (αSMA)- lymphatic capillaries are increased, whereas PDPN+ /αSMA+ collecting LVs are decreased significantly in the inflamed periodontal tissues. Both mouse models of periodontitis have delayed lymph flow in periodontal tissues, increased TRAP-positive osteoclasts, and significant alveolar bone loss. Importantly, the local administration of adeno-associated virus for vascular endothelial growth factor C, the major growth factor that promotes lymphangiogenesis, increases the area and number of PDPN+ /αSMA+ collecting LVs, promotes local lymphatic drainage, and reduces alveolar bone loss in both models of periodontitis. Lastly, LYVE1+ /αSMA- lymphatic capillaries are increased, whereas LYVE1+ /αSMA+ collecting LVs are decreased significantly in gingival tissues of patients with chronic periodontitis compared with those of clinically healthy controls. Thus, our findings reveal an important role of local lymphatic drainage in periodontal inflammation-mediated alveolar bone loss. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Fang-Ji-Huang-Qi-Tang Attenuates Degeneration of Early-Stage KOA Mice Related to Promoting Joint Lymphatic Drainage Function

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by the breakdown of articular cartilage, subchondral bone remodeling, and inflammation of the synovium. In this study, we investigated whether Fang-Ji-Huang-Qi-Tang (FJHQT) decoction improved the joint structure of OA or delayed the process of knee joint degeneration in OA mice by promoting lymphatic drain function. The mice were randomly divided into four groups, the sham group, the PBS group, the FJHQT-treated group, and the Mobic-treated group. The mice in each group were tested for lymphatic draining function at 4, 6, 8, and 10 weeks postsurgery (WPS), then sacrificed (N = 10/group). Using a near-infrared indocyanine green (NIR-ICG) lymphatic imaging system, we found that the lymphatic drain function was significantly reduced in the PBS group compared with the sham group. After treatment with the FJHQT decoction, the lymphatic draining function improved at 4 wps and 6 wps. The results of the analysis indicated a strong correlation between lymphatic draining function (ICG clearance) and the degree of joint structural damage (OARSI score). By Alcian blue/orange G (ABOG) staining of the paraffin sections, the FJHQT-treated group exhibited less cartilage destruction and lower OARSI scores. Moreover, the result of immunohistochemical staining (IHC) shows that FJHQT decoction increased the content of type II collagen in knee joints of OA mice at 4 wps and 6 wps. By the double immunofluorescence staining of podoplanin and smooth muscle actin in the paraffin sections, the capillaries and mature lymphatics in the FJHQT group increased at 4 wps. In conclusion, the FJHQT decoction can increase lymphatic vessel number, promote joint lymphatic draining function, and postpone knee osteoarthritis pathologic progression in the early stage of a collagen-induced mouse model. Therefore, the application of sufficient lymphatic drainage in the knee joint may be a new treatment method for knee joint osteoarthritis (KOA).

Ginsenoside Rg1 promotes lymphatic drainage and improves chronic inflammatory arthritis

OBJECTIVE

The lymphatic system plays an important role in joint diseases. This study aimed to evaluate the effects of ginsenoside Rg1 on lymphatic drainage and accumulation of inflammatory products in the joints.

METHODS

Two-month-old transgenic mice that overexpress tumor necrosis factor alpha (TNF-α; TNF-Tg) were used as the animal models. Ginsenoside Rg1 was administered for 12 weeks and the lymphatic drainage in the mice was evaluated using near infrared-indocyanine green (NIR-ICG) lymphatic imaging system. The clinical symptoms of arthritis were evaluated weekly. The ankle and knee joints were harvested for hematoxylin-eosin (HE), alcian blue/orange G (ABOG), and tartrate-resistant acid phosphatase (TRAP) staining, and the foot dorsal skin was used for whole-mount immuno-staining. Simultaneously, the serum levels of IL-6 and TNF-α were detected using enzyme-linked immunosorbent assay (ELISA).

RESULTS

Ginsenoside Rg1 significantly improved the lymphatic drainage function, reduced synovial inflammation and bone erosion, decreased serum IL-6 and TNF-α concentration, and increased smooth muscle coverage on the collecting lymphatic vessels in the foot skin of the TNF-Tg mice. Furthermore, ginsenoside Rg1 treatment for 12 weeks did not cause any damage to the liver and kidney tissues.

CONCLUSION

Ginsenoside Rg1 improves lymphatic drainage and joint inflammation in TNF-Tg mice. Therefore, ginsenoside Rg1 has the potential to be a candidate drug for the treatment of inflammatory arthritis.

Role of Liposome Size, Surface Charge, and PEGylation on Rheumatoid Arthritis Targeting Therapy

Rheumatoid arthritis (RA) is a chronic, systemic, progressive autoimmune disease. The vascular permeability of inflamed joints in RA makes it a natural candidate for passive targeting, similar to the enhanced permeability and retention (EPR) effect in solid tumors. Thus, various therapeutic drugs have been encapsulated in nanocarriers to achieve longer in vivo circulation times and improve RA targeting. Although liposomes are the most widely used nanocarriers for RA treatment, the effects of physical and chemical characteristics of liposomes, such as particle sizes, surface charge, polyethylene glycol (PEG) chain length, and PEG concentration, on their passive RA targeting effect have not been fully elucidated. Here, we systematically investigated the effects of physical and chemical properties of liposomes on circulation time and conducted preliminary studies on their passive targeting mechanisms. A series of liposomes with different particle sizes (70, 100, 200, and 350 nm), surface charges (positive, negative, slight positive, and slight negative), PEG chain lengths (1, 2, and 5 kDa), and concentrations (5, 10, and 20% w/w of total lipid) were prepared by lipid film dispersion and extrusion. The pharmacokinetics of liposomes with different formulas were evaluated with a fluorescence microplate reader. A collagen-induced arthritis (CIA) mouse model was utilized to mimic RA pathological conditions and to evaluate the targeting and efficacy of liposomes with different properties using a near-infrared fluorescence imaging system. Uptake of fluorescent liposomes by various synovial cells was measured by flow cytometry. The results indicated that liposomes with 100 nm diameter, a slight negative charge, and 10% incorporation of 5 kDa PEG had better in vivo circulation time and inflamed joint targeting than did other liposomes. Dexamethasone (Dex) was encapsulated into optimized liposomes as an active ingredient for RA treatment. Pharmacodynamic studies demonstrated that Dex liposomes could significantly improve the antiarthritic efficacy of Dex in a CIA mouse model of RA. This study also found that the retention mechanism of RA was mainly increased because of the uptake of liposomes by fibroblasts and macrophages in inflamed joints. This study provides a persuasive explanation for passive RA targeting by liposomes and advances our ability to treat RA with nanomedicine.

Application of microscale culture technologies for studying lymphatic vessel biology

Immense progress in microscale engineering technologies has significantly expanded the capabilities of in vitro cell culture systems for reconstituting physiological microenvironments that are mediated by biomolecular gradients, fluid transport, and mechanical forces. Here, we examine the innovative approaches based on microfabricated vessels for studying lymphatic biology. To help understand the necessary design requirements for microfluidic models, we first summarize lymphatic vessel structure and function. Next, we provide an overview of the molecular and biomechanical mediators of lymphatic vessel function. Then we discuss the past achievements and new opportunities for microfluidic culture models to a broad range of applications pertaining to lymphatic vessel physiology. We emphasize the unique attributes of microfluidic systems that enable the recapitulation of multiple physicochemical cues in vitro for studying lymphatic pathophysiology. Current challenges and future outlooks of microscale technology for studying lymphatics are also discussed. Collectively, we make the assertion that further progress in the development of microscale models will continue to enrich our mechanistic understanding of lymphatic biology and physiology to help realize the promise of the lymphatic vasculature as a therapeutic target for a broad spectrum of diseases.

Regulation of Immune Function by the Lymphatic System in Lymphedema

The lymphatic vasculature has traditionally been thought to play a passive role in the regulation of immune responses by transporting antigen presenting cells and soluble antigens to regional lymph nodes. However, more recent studies have shown that lymphatic endothelial cells regulate immune responses more directly by modulating entry of immune cells into lymphatic capillaries, presenting antigens on major histocompatibility complex proteins, and modulating antigen presenting cells. Secondary lymphedema is a disease that develops when the lymphatic system is injured during surgical treatment of cancers or is damaged by infections. We have used mouse models of lymphedema in order to understand the effects of chronic lymphatic injury on immune responses and have shown that lymphedema results in a mixed T helper cell and T regulatory cell (Treg) inflammatory response. Prolonged T helper 2 biased immune responses in lymphedema regulate the pathology of this disease by promoting tissue fibrosis, inhibiting formation of collateral lymphatics, decreasing lymphatic vessel pumping capacity, and increasing lymphatic leakiness. Treg infiltration following lymphatic injury results from proliferation of natural Tregs and suppresses innate and adaptive immune responses. These studies have broad clinical relevance since understanding how lymphatic injury in lymphedema can modulate immune responses may provide a template with which we can study more subtle forms of lymphatic injury that may occur in physiologic conditions such as aging, obesity, metabolic tumors, and in the tumor microenvironment.

Inflammation and Lymphatic Function

The lymphatic vasculature plays a crucial role in regulating the inflammatory response by influencing drainage of extravasated fluid, inflammatory mediators, and leukocytes. Lymphatic vessels undergo pronounced enlargement in inflamed tissue and display increased leakiness, indicating reduced functionality. Interfering with lymphatic expansion by blocking the vascular endothelial growth factor C (VEGF-C)/vascular endothelial growth factor receptor 3 (VEGFR-3) signaling axis exacerbates inflammation in a variety of disease models, including inflammatory bowel disease (IBD), rheumatoid arthritis and skin inflammation. In contrast, stimulation of the lymphatic vasculature, e.g., by transgenic or viral overexpression as well as local injections of VEGF-C, has been shown to reduce inflammation severity in models of rheumatoid arthritis, skin inflammation, and IBD. Strikingly, the induced expansion of the lymphatic vasculature improves lymphatic function as assessed by the drainage of dyes, fluorescent tracers or inflammatory cells and labeled antigens. The drainage performance of lymphatic vessels is influenced by vascular permeability and pumping activity, which are influenced by VEGF-C/VEGFR-3 signaling as well as several inflammatory mediators, including TNF-α, IL-1β, and nitric oxide. Considering the beneficial effects of lymphatic activation in inflammation, administration of pro-lymphangiogenic factors like VEGF-C, preferably in a targeted, inflammation site-specific fashion, represents a promising therapeutic approach in the setting of inflammatory pathologies.

Osthole attenuates angiogenesis in an orthotopic mouse model of hepatocellular carcinoma via the downregulation of nuclear factor-κB and vascular endothelial growth factor

Osthole has been demonstrated to have antitumor activity. Previous studies by our group indicated that osthole effectively inhibited tumor growth in hepatocellular carcinoma (HCC) through the induction of apoptosis and enhancement of antitumor immune responses in mice. The importance of angiogenesis in the proliferation, invasion and metastasis of tumor cells in HCC is well established. The present study aimed to investigate the effects of osthole on angiogenesis in an orthotopic mouse model of HCC. Orthotopic HCC in mice was established, and osthole at 61, 122 and 244 mg/kg was administered intraperitoneally once daily to the tumor-bearing mice for 14 consecutive days. Immunohistochemistry was performed to analyze the microvessel density (MVD) of tissues, and the level of vascular endothelial growth factor (VEGF) was measured by ELISA. The protein levels of nuclear factor-κB (NF-κB) p65 and IκB-α were also detected by western blotting. MVD was positively correlated with tumor weight in the orthotopic mouse model of HCC. Osthole administration significantly decreased MVD in tumor and adjacent tissues, and inhibited tumor growth. Furthermore, osthole downregulated the expression of VEGF and NF-κB p65, and upregulated IκB-α expression in tumor and adjacent tissues. To the best of our knowledge, the results of the present study demonstrated for the first time that osthole inhibits angiogenesis in an orthotopic mouse model of HCC, which may be one of the mechanisms underlying the anti-HCC activity of osthole, which in turn may be mediated by the NF-κB/VEGF signaling pathway. Therefore, osthole, a potential angiogenesis inhibitor and immune system enhancer, may be a promising lead compound for the treatment of HCC.

Obstructive Lymphangitis Precedes Colitis in Murine Norovirus-Infected Stat1-Deficient Mice

Murine norovirus (MNV) is an RNA virus that can prove lethal in mice with impaired innate immunity. We found that MNV-4 infection of Stat1-/- mice was not lethal, but produced a 100% penetrant, previously undescribed lymphatic phenotype characterized by chronic-active lymphangitis with hepatitis, splenitis, and chronic cecal and colonic inflammation. Lesion pathogenesis progressed from early ileal enteritis and regional dilated lymphatics to lymphangitis, granulomatous changes in the liver and spleen, and, ultimately, typhlocolitis. Lesion development was neither affected by antibiotics nor reproduced by infection with another enteric RNA virus, rotavirus. MNV-4 infection in Stat1-/- mice decreased expression of vascular endothelial growth factor (Vegf) receptor 3, Vegf-c, and Vegf-d and increased interferon (Ifn)-γ, tumor necrosis factor-α, and inducible nitric oxide synthase. However, anti-IFN-γ and anti-tumor necrosis factor-α antibody treatment did not attenuate the histologic lesions. Studies in Ifnαβγr-/- mice suggested that canonical signaling via interferon receptors did not cause MNV-4-induced disease. Infected Stat1-/- mice had increased STAT3 phosphorylation and expressed many STAT3-regulated genes, consistent with our findings of increased myeloid cell subsets and serum granulocyte colony-stimulating factor, which are also associated with increased STAT3 activity. In conclusion, in Stat1-/- mice, MNV-4 induces lymphatic lesions similar to those seen in Crohn disease as well as hepatitis, splenitis, and typhlocolitis. MNV-4-infected Stat1-/- mice may be a useful model to study mechanistic associations between viral infections, lymphatic dysfunction, and intestinal inflammation in a genetically susceptible host.

Targeting lymphatic function as a novel therapeutic intervention for rheumatoid arthritis

Although clinical outcomes for patients with rheumatoid arthritis (RA) have greatly improved with the use of biologic and conventional DMARDs, approximately 40% of patients do not achieve primary clinical outcomes in randomized trials, and only a small proportion achieve lasting remission. Over the past decade, studies in murine models point to the critical role of the lymphatic system in the pathogenesis and therapy of inflammatory-erosive arthritis, presumably by the removal of catabolic factors, cytokines and inflammatory cells from the inflamed synovium. Murine studies demonstrate that lymphatic drainage increases at the onset of inflammatory-erosive arthritis but, as inflammation progresses to a more chronic phase, lymphatic clearance declines and both structural and cellular changes are observed in the draining lymph node. Specifically, chronic damage to the lymphatic vessel from persistent inflammation results in loss of lymphatic vessel contraction followed by lymph node collapse, reduced lymphatic drainage, and ultimately severe synovitis and joint erosion. Notably, clinical pilot studies in patients with RA report lymph node changes following treatment, and thus draining lymphatic vessels and nodes could represent a potential biomarker of arthritis activity and response to therapy. Most importantly, targeting lymphatics represents an innovative strategy for therapeutic intervention for RA.

Tertiary Lymphoid Structures Among the World of Noncanonical Ectopic Lymphoid Organizations

Tertiary lymphoid structures (TLOs), also known as ectopic lymphoid structures, are associated with chronic infections and inflammatory diseases. Despite their association with pathology, these structures are actually a normal, albeit transient, component of the immune system and facilitate local immune responses that are meant to mitigate inflammation and resolve infection. Many of the mechanisms controlling the formation and function of tertiary lymphoid structures have been identified, in part by experimentally triggering their formation using defined stimuli under controlled conditions. Here, we introduce the experimental and pathological conditions in which tertiary lymphoid tissues are formed, describe the mechanisms linked to their formation, and discuss their functions in the context of both infection and inflammation.

Application of Pharmacokinetics Modelling to Predict Human Exposure of a Cationic Liposomal Subunit Antigen Vaccine System

The pharmacokinetics of a liposomal subunit antigen vaccine system composed of the cationic lipid dimethyldioctadecylammonium bromide (DDA) and the immunostimulatory agent trehalose 6,6-dibehenate (TDB) (8:1 molar ratio) combined with the Ag85B-ESAT-6 (H1) antigen were modelled using mouse in-vivo data. Compartment modelling and physiologically based pharmacokinetics (PBPK) were used to predict the administration site (muscle) and target site (lymph) temporal concentration profiles and factors governing these. Initial estimates using compartmental modelling established that quadriceps pharmacokinetics for the liposome demonstrated a long half-life (22.6 days) compared to the associated antigen (2.62 days). A mouse minimal-PBPK model was developed and successfully predicted quadriceps liposome and antigen pharmacokinetics. Predictions for the popliteal lymph node (PLN) aligned well at earlier time-points. A local sensitivity analysis highlighted that the predicted AUC_muscle was sensitive to the antigen degradation constant k_deg (resulting in a 3-log change) more so than the fraction escaping the quadriceps (f_e) (resulting in a 10-fold change), and the predicted AUC_PLN was highly sensitive to f_e. A global sensitivity analysis of the antigen in the muscle demonstrated that model predictions were within the 50th percentile for predictions and showed acceptable fits. To further translate in-vitro data previously generated by our group, the mouse minimal-PBPK model was extrapolated to humans and predictions made for antigen pharmacokinetics in muscle and PLN. Global analysis demonstrated that both k_deg and f_e had a minimal impact on the resulting simulations in the muscle but a greater impact in the PLN. In summary, this study has predicted the in-vivo fate of DDA:TDB:H1 in humans and demonstrated the roles that formulation degradation and fraction escaping the depot site can play upon the overall depot effect within the site of administration.

Vascular endothelial growth factor-C ameliorates renal interstitial fibrosis through lymphangiogenesis in mouse unilateral ureteral obstruction

Renal fibrosis is the final common pathway of chronic kidney diseases. Lymphatic vessel (LV) proliferation is found in human renal diseases and other fibrotic diseases, suggesting that lymphangiogenesis is associated with the progression or suppression of kidney diseases. However, the purpose of LV proliferation is not completely understood. We investigated the effect of vascular endothelial growth factor (VEGF)-C on lymphangiogenesis, inflammation, and fibrosis in the mouse kidney using the unilateral ureteral obstruction (UUO) model. In UUO mice, significant proliferation of LVs was accompanied by tubulointerstitial nephritis and fibrosis. We continuously administered recombinant human VEGF-C to UUO model mice using an osmotic pump (UUO+VEGF-C group). Lymphangiogenesis was significantly induced in the UUO+VEGF-C group compared with the vehicle group, despite similar numbers of capillaries in both groups. The number of infiltrating macrophages, and levels of inflammatory cytokines and transforming growth factor-β1 were reduced in the UUO+VEGF-C group compared with the vehicle group. Renal fibrosis was consequently attenuated in the UUO+VEGF-C group. In cultured lymphatic endothelial cells, administration of VEGF-C increased the activity and proliferation of lymphatic endothelial cells (LECs) and expression of adhesion molecules such as vascular cell adhesion molecule-1. These findings suggest that induction of lymphangiogenesis ameliorates inflammation and fibrosis in the renal interstitium. Enhancement of the VEGF-C signaling pathway in LECs may be a therapeutic strategy for renal fibrosis.

Association of Increased F4/80high Macrophages With Suppression of Serum-Transfer Arthritis in Mice With Reduced FLIP in Myeloid Cells

OBJECTIVE

Macrophages are critical in the pathogenesis of rheumatoid arthritis (RA). We recently demonstrated that FLIP is necessary for the differentiation and/or survival of macrophages. We also showed that FLIP is highly expressed in RA synovial macrophages. This study was undertaken to determine if a reduction in FLIP in mouse macrophages reduces synovial tissue macrophages and ameliorates serum-transfer arthritis.

METHODS

Mice with Flip deleted in myeloid cells (Flip^f/f LysM^c/+ mice) and littermate controls were used. Arthritis was induced by intraperitoneal injection of K/BxN serum. Disease severity was evaluated by clinical score and change in ankle thickness, and joints were examined by histology and immunohistochemistry. Cells were isolated from the ankles and bone marrow of the mice and examined by flow cytometry, real-time quantitative reverse transcriptase-polymerase chain reaction, or Western blotting.

RESULTS

In contrast to expectations, Flip^f/f LysM^c/+ mice developed more severe arthritis early in the clinical course, but peak arthritis was attenuated and the resolution phase more complete than in control mice. Prior to the induction of serum-transfer arthritis, the number of tissue-resident macrophages was reduced. On day 9 after arthritis induction, the number of F4/80^high macrophages in the joints of the Flip^f/f LysM^c/+ mice was not decreased, but increased. FLIP was reduced in the F4/80^high macrophages in the ankles of the Flip^f/f LysM^c/+ mice, while F4/80^high macrophages expressed an antiinflammatory phenotype in both the Flip^f/f LysM^c/+ and control mice.

CONCLUSION

Our observations suggest that reducing FLIP in macrophages by increasing the number of antiinflammatory macrophages may be an effective therapeutic approach to suppress inflammation, depending on the disease stage.

Novel role of immature myeloid cells in formation of new lymphatic vessels associated with inflammation and tumors

Inflammation triggers an immune cell-driven program committed to restoring homeostasis to injured tissue. Central to this process is vasculature restoration, which includes both blood and lymphatic networks. Generation of new vessels or remodeling of existing vessels are also important steps in metastasis-the major cause of death for cancer patients. Although roles of the lymphatic system in regulation of inflammation and cancer metastasis are firmly established, the mechanisms underlying the formation of new lymphatic vessels remain a subject of debate. Until recently, generation of new lymphatics in adults was thought to occur exclusively through sprouting of existing vessels without help from recruited progenitors. However, emerging findings from clinical and experimental studies show that lymphoendothelial progenitors, particularly those derived from immature myeloid cells, play an important role in this process. This review summarizes current evidence for the existence and significant roles of myeloid-derived lymphatic endothelial cell progenitors (M-LECPs) in generation of new lymphatics. We describe specific markers of M-LECPs and discuss their biologic behavior in culture and in vivo, as well as currently known molecular mechanisms of myeloid-lymphatic transition (MLT). We also discuss the implications of M-LECPs for promoting adaptive immunity, as well as cancer metastasis. We conclude that improved mechanistic understanding of M-LECP differentiation and its role in adult lymphangiogenesis may lead to new therapeutic approaches for correcting lymphatic insufficiency or excessive formation of lymphatic vessels in human disorders.

Brief Report: Treatment of Tumor Necrosis Factor-Transgenic Mice With Anti-Tumor Necrosis Factor Restores Lymphatic Contractions, Repairs Lymphatic Vessels, and May Increase Monocyte/Macrophage Egress

OBJECTIVE

Recent studies have demonstrated that there is an inverse relationship between lymphatic egress and inflammatory arthritis in affected joints. As a model, tumor necrosis factor (TNF)-transgenic mice develop advanced arthritis following draining lymph node (LN) collapse, and loss of lymphatic contractions downstream of inflamed joints. It is unknown if these lymphatic deficits are reversible. This study was undertaken to test the hypothesis that anti-TNF therapy reduces advanced erosive inflammatory arthritis, associated with restoration of lymphatic contractions, repair of damaged lymphatic vessels, and evidence of increased monocyte egress.

METHODS

TNF-transgenic mice with advanced arthritis and collapsed popliteal LNs were treated with anti-TNF monoclonal antibody (10 mg/kg weekly) or placebo for 6 weeks, and effects on knee synovitis, lymphatic vessel ultrastructure and function, and popliteal LN cellularity were assessed by ultrasound, histology, transmission electron microscopy (TEM), near-infrared indocyanine green imaging, and flow cytometry.

RESULTS

Anti-TNF therapy significantly decreased synovitis (∼5-fold; P < 0.05 versus placebo), restored lymphatic contractions, and significantly increased the number of popliteal LN monocyte/macrophages (∼2-fold; P < 0.05 versus placebo). TEM demonstrated large activated macrophages attached to damaged lymphatic endothelium in mice with early arthritis, extensively damaged lymphatic vessels in placebo-treated mice with advanced arthritis, and rolling leukocytes in repaired lymphatic vessels in mice responsive to anti-TNF therapy.

CONCLUSION

These findings support the concept that anti-TNF therapy ameliorates erosive inflammatory arthritis, in part via restoration of lymphatic vessel contractions and potential enhancement of inflammatory cell egress.

VEGFR-3 Expression in Oral Lichen Planus

Background and objective: Given the postulated the role of inflammation and possible contribution of lymphangiogenesis in oral lichen planus, this study aimed to assess any associated presence of VEGFR-3. Material and Methods: This cross-sectional study was performed on 52 formalin fixed and paraffin embedded blocks of oral lichen planus (pathological diagnosis based on Modified WHO criteria), comprising 25 of erosive and 27 of reticular type, along with 60 samples of normal mucosa (with minimal inflammation from clinical and histopathological aspects) obtained at crown lengthening surgery. Four micron sections were cut from paraffin blocks and stained with H and E for confirmation of diagnosis and by immunohistochemistry with primary antibodies against VEGFR-3. Negative controls were provided by omission of primary antibody and placenta was considered as a positive control. Data were analyzed by Chi-square, Mann-Whitney and Kruskal-wallis tests and P <0.05 was considered statistically significant. Findings: VEGFR-3 expression was apparent in 61.5% of lichen planus specimens and 5% of those from normal mucosa (p<0.001). Also, the average number of stained vessels was significantly higher in oral lichen planus than in normal mucosa (p<0.001). VEGFR-3 expression in oral lichen planus (p=0.262) and the average number of stained vessels (p=0.092) demonstrated no significant difference according to the type. Conclusion: It appears that VEGFR-3 expression might be involved in the pathogenesis of the oral lichen planus through increasing lymphatic vessels and lymphangiogenesis.

VEGF Pathways in the Lymphatics of Healthy and Diseased Heart

Cardiac lymphatic system is a rare focus of the modern cardiovascular research. Nevertheless, the growing body of evidence is depicting lymphatic endothelium as an important functional unit in healthy and diseased myocardium. Since the discovery of angiogenic VEGF-A in 1983 and lymphangiogenic VEGF-C in 1997, an increasing amount of knowledge has accumulated on the essential roles of VEGF ligands and receptors in physiological and pathological angiogenesis and lymphangiogenesis. Tissue adaptation to several stimuli such as hypoxia, pathogen invasion, degenerative process and inflammation often involves coordinated changes in both blood and lymphatic vessels. As lymphatic vessels are involved in the initiation and resolution of inflammation and regulation of tissue edema, VEGF family members may have important roles in myocardial lymphatics in healthy and in cardiac disease. We will review the properties of VEGF ligands and receptors concentrating on their lymphatic vessel effects first in normal myocardium and then in cardiac disease.

VEGFR-2 reduces while combined VEGFR-2 and -3 signaling increases inflammation in apical periodontitis

BACKGROUND

In apical periodontitis, oral pathogens provoke an inflammatory response in the apical area that induces bone resorptive lesions. In inflammation, angio- and lymphangiogenesis take place. Vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) are key players in these processes and are expressed in immune cells and endothelial cells in the lesions.

OBJECTIVE

We aimed at testing the role of VEGFR-2 and -3 in periapical lesion development and investigated their role in lymphangiogenesis in the draining lymph nodes.

DESIGN

We induced lesions by pulp exposure in the lower first molars of C57BL/6 mice. The mice received IgG injections or blocking antibodies against VEGFR-2 (anti-R2), VEGFR-3 (anti-R3), or combined VEGFR-2 and -3, starting on day 0 until day 10 or 21 post-exposure.

RESULTS

Lesions developed faster in the anti-R2 and anti-R3 group than in the control and anti-R2/R3 groups. In the anti-R2 group, a strong inflammatory response was found expressed as increased number of neutrophils and osteoclasts. A decreased level of pro-inflammatory cytokines was found in the anti-R2/R3 group. Lymphangiogenesis in the draining lymph nodes was inhibited after blocking of VEGFR-2 and/or -3, while the largest lymph node size was seen after anti-R2 treatment.

CONCLUSIONS

We demonstrate an anti-inflammatory effect of VEGFR-2 signaling in periapical lesions which seems to involve neutrophil regulation and is independent of angiogenesis. Combined signaling of VEGFR-2 and -3 has a pro-inflammatory effect. Lymph node lymphangiogenesis is promoted through activation of VEGFR-2 and/or VEGFR-3.

Lymphatic imaging to assess rheumatoid flare: mechanistic insights and biomarker potential

Proliferation of draining lymphatic vessels coupled with dynamic changes in lymph node volume and flow are characteristic features in rheumatoid arthritis (RA). Furthermore, impaired lymph egress from inflamed synovium is associated with joint flare in murine models of inflammatory-erosive arthritis. Unfortunately, advances towards a greater understanding of lymphatic changes in RA pathogenesis have been slow due to the absence of outcome measures to quantify lymphatic function in vivo. While lymphoscintigraphy is the current standard to assess lymphedema and sentinel lymph nodes in cancer patients, its sensitivity and specificity are inadequate to study lymphatics in RA. The emergence of high-resolution MRI, power Doppler ultrasound, and near-infrared imaging that permits real-time quantification of lymphatic function in animal models has been a major advance, and these techniques have produced a new paradigm of altered lymphatic function that underlies both acute arthritic flare and chronic inflammation. In acute flare, lymphatic drainage increases several fold, whereas no lymphatic contractions are detected in lymph vessels draining chronic arthritic joints. Moreover, these outcomes are now being adapted to study lymphatics in RA towards the development of novel biomarkers of arthritic flare and the discovery of new therapeutic targets. In particular, interventions that directly increase lymphatic egress from diseased joints by opening collateral lymphatic vessels, and that restore lymphatic vessel contractions, provide novel therapeutic approaches with potential for minimal toxicity and immunosuppression. To summarize the origins of this field, recent advances, and future directions, we herein review: current knowledge of lymphatics in RA based on classic literature; new in-vivo imaging modalities that have elucidated how lymphatics modulate acute versus chronic joint inflammation in murine models; and how these preclinical outcome measures are being translated to study lymphatic function in RA inflammation and how effective RA therapies alter lymphatic flow and lymph nodes draining flaring joints.

Trial registration: ClinicalTrials.gov NCT02680067. Registered 7 December 2015; ClinicalTrials.gov NCT01098201. Registered 30 March 2010; and ClinicalTrials.gov NCT01083563. Registered 8 March 2010.

Du-Huo-Ji-Sheng-Tang Attenuates Inflammation of TNF-Tg Mice Related to Promoting Lymphatic Drainage Function

To investigate whether Du-Huo-Ji-Sheng-Tang (DHJST) attenuate inflammation of RA related to lymphatic drainage function in vivo, we treated eight 3-month-old TNF-Tg mice with DHJST (12 g/kg) or the same volume of physiological saline once every day for 12 weeks, and 3-month-old WT littermates were used as negative control. After twelve weeks, we performed NIR-ICG imaging and found that DHJST increased the ICG clearance at the footpad and the pulse of efferent lymphatic vessel between popliteal lymph node and footpad. Histology staining at ankle joints showed that DHJST decreases synovial inflammation, bone erosion, cartilage erosion, and TRAP+ osteoclast area in TNF-Tg mice. Immunohistochemical staining by using anti-Lyve-1 and anti-podoplanin antibody showed that DHJST stimulated lymphangiogenesis in ankle joints of TNF-Tg mice. And zebrafish study suggested that DHJST promoted the formation of lymphatic thoracic duct. In conclusion, DHJST inhibits inflammation severity and promotes lymphangiogenesis and lymphatic drainage function of TNF-Tg mice.

Lymphatic endothelial cells efferent to inflamed joints produce iNOS and inhibit lymphatic vessel contraction and drainage in TNF-induced arthritis in mice

Background

In this study, we sought to determine the cellular source of inducible nitric oxide synthase (iNOS) induced in lymphatic endothelial cells (LECs) in response to tumor necrosis factor (TNF), the effects of iNOS on lymphatic smooth muscle cell (LSMC) function and on the development of arthritis in TNF-transgenic (TNF-Tg) mice, and whether iNOS inhibitors improve lymphatic function and reduce joint destruction in inflammatory erosive arthritis.

Methods

We used quantitative polymerase chain reactions, immunohistochemistry, histology, and near-infrared imaging to examine (1) iNOS expression in podoplanin + LECs and lymphatic vessels from wild-type (WT) and TNF-Tg mice, (2) iNOS induction by TNF in WT LECs, (3) the effects of iNOS inhibitors on expression of functional muscle genes in LSMCs, and (4) the effects of iNOS inhibitors on lymphatic vessel contraction and drainage, as well as the severity of arthritis, in TNF-Tg mice.

Results

LECs from TNF-Tg mice had eight fold higher iNOS messenger RNA levels than WT cells, and iNOS expression was confirmed immunohistochemically in podoplanin + LECs in lymphatic vessels from inflamed joints. TNF (0.1 ng/ml) increased iNOS levels 40-fold in LECs. LSMCs cocultured with LECs pretreated with TNF had reduced expression of functional muscle genes. This reduction was prevented by ferulic acid, which blocked nitric oxide production. Local injection of L-N⁶-(1-iminoethyl)lysine 5-tetrazole-amide into inflamed paws of TNF-Tg mice resulted in recovery of lymphatic vessel contractions and drainage. Treatment of TNF-Tg mice with ferulic acid reduced synovial inflammation as well as cartilage and bone erosion, and it also restored lymphatic contraction and drainage.

Conclusions

iNOS is produced primarily by LECs in lymphatic vessel efferent from inflamed joints of TNF-Tg mice in response to TNF and inhibits LSMC contraction and lymph drainage. Ferulic acid represents a potential new therapy to restore lymphatic function and thus improve inflammatory arthritis by inhibiting local production of nitric oxide by LSMCs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-0963-8) contains supplementary material, which is available to authorized users.

Involvement of corneal lymphangiogenesis in a mouse model of allergic eye disease

PURPOSE

The contribution of lymphangiogenesis (LA) to allergy has received considerable attention and therapeutic inhibition of this process via targeting VEGF has been considered. Likewise, certain inflammatory settings affecting the ocular mucosa can trigger pathogenic LA in the naturally avascular cornea. Chronic inflammation in allergic eye disease (AED) impacts the conjunctiva and cornea, leading to sight threatening conditions. However, whether corneal LA is involved is completely unknown. We addressed this using a validated mouse model of AED.

METHODS

Allergic eye disease was induced by ovalbumin (OVA) immunization and chronic OVA exposure. Confocal microscopy of LYVE-1-stained cornea allowed evaluation of corneal LA, and qRT-PCR was used to evaluate expression of VEGF-C, -D, and -R3 in these mice. Administration of VEGF receptor (R) inhibitor was incorporated to inhibit corneal LA in AED. Immune responses were evaluated by in vitro OVA recall responses of T cells, and IgE levels in the serum.

RESULTS

Confocal microscopy of LYVE-1-stained cornea revealed the distinct presence of corneal LA in AED, and corroborated by increased corneal expression of VEGF-C, -D, and -R3. Importantly, prevention of corneal LA in AED via VEGFR inhibition was associated with decreased T helper two responses and IgE production. Furthermore, VEGFR inhibition led a significant reduction in clinical signs of AED.

CONCLUSIONS

Collectively, these data reveal that there is a distinct involvement of corneal LA in AED. Furthermore, VEGFR inhibition prevents corneal LA and consequent immune responses in AED.