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

High-throughput micro-CT analysis identifies sex-dependent biomarkers of erosive arthritis in TNF-Tg mice and differential response to anti-TNF therapy

BACKGROUND

Development of reliable disease activity biomarkers is critical for diagnostics, prognostics, and novel drug development. Although computed tomography (CT) is the gold-standard for quantification of bone erosions, there are no consensus approaches or rationales for utilization of specific outcome measures of erosive arthritis in complex joints. In the case of preclinical models, such as sexually dimorphic tumor necrosis factor transgenic (TNF-Tg) mice, disease severity is routinely quantified in the ankle through manual segmentation of the talus or small regions of adjacent bones primarily due to the ease in measurement. Herein, we sought to determine the particular hindpaw bones that represent reliable biomarkers of sex-dependent disease progression to guide future investigation and analysis.

METHODS

Hindpaw micro-CT was performed on wild-type (n = 4 male, n = 4 female) and TNF-Tg (n = 4 male, n = 7 female) mice at monthly intervals from 2-5 (females) and 2-8-months (males) of age, since female TNF-Tg mice exhibit early mortality from cardiopulmonary disease at approximately 5-6-months. Further, 8-month-old WT (n = 4) and TNF-Tg males treated with anti-TNF monoclonal antibodies (n = 5) or IgG placebo isotype controls (n = 6) for 6-weeks were imaged with micro-CT every 3-weeks. For image analysis, we utilized our recently developed high-throughput and semi-automated segmentation strategy in Amira software. Synovial and osteoclast histology of ankle joints was quantified using Visiopharm.

RESULTS

First, we demonstrated that the accuracy of automated segmentation, determined through analysis of ~9000 individual bones by a single user, was comparable in wild-type and TNF-Tg hindpaws before correction (79.2±8.9% vs 80.1±5.1%, p = 0.52). Compared to other bone compartments, the tarsal region demonstrated a sudden, specific, and significant bone volume reduction in female TNF-Tg mice, but not in males, by 5-months (4-months 4.3± 0.22 vs 5-months 3.4± 0.62 mm3, p<0.05). Specifically, the cuboid showed significantly reduced bone volumes at early timepoints compared to other tarsals (i.e., 4-months: Cuboid -24.1±7.2% vs Talus -9.0±5.9% of 2-month baseline). Additional bones localized to the anterolateral region of the ankle also exhibited dramatic erosions in the tarsal region of females, coinciding with increased synovitis and osteoclasts. In TNF-Tg male mice with severe arthritis, the talus and calcaneus exhibited the most sensitive response to anti-TNF therapy measured by effect size of bone volume change over treatment period.

CONCLUSIONS

We demonstrated that sexually dimorphic changes in arthritic hindpaws of TNF-Tg mice are bone-specific, where the cuboid serves as a reliable early biomarker of erosive arthritis in female mice. Adoption of automated segmentation approaches in pre-clinical or clinical models has potential to translate quantitative biomarkers to monitor bone erosions in disease and evaluate therapeutic efficacy.

Role of the Lymphatics in Cardiac Disease

Cardiovascular diseases remain the largest cause of death worldwide with recent evidence increasingly attributing the development and progression of these diseases to an exacerbated inflammatory response. As a result, significant research is now focused on modifying the immune environment to prevent the disease progression. This in turn has highlighted the lymphatic system in the pathophysiology of cardiovascular diseases owing, in part, to its established function in immune cell surveillance and trafficking. In this review, we highlight the role of the cardiac lymphatic system and its potential as an immunomodulatory therapeutic target in selected cardiovascular diseases.

Nerve growth factor receptor limits inflammation to promote remodeling and repair of osteoarthritic joints

Osteoarthritis (OA) is a painful, incurable disease affecting over 500 million people. Recent clinical trials of the nerve growth factor (NGF) inhibitors in OA patients have suggested adverse effects of NGF inhibition on joint structure. Here we report that nerve growth factor receptor (NGFR) is upregulated in skeletal cells during OA and plays an essential role in the remodeling and repair of osteoarthritic joints. Specifically, NGFR is expressed in osteochondral cells but not in skeletal progenitor cells and induced by TNFα to attenuate NF-κB activation, maintaining proper BMP-SMAD1 signaling and suppressing RANKL expression in mice. NGFR deficiency hyper-activates NF-κB in murine osteoarthritic joints, which impairs bone formation and enhances bone resorption as exemplified by a reduction in subchondral bone and osteophytes. In human OA cartilage, NGFR is also negatively associated with NF-κB activation. Together, this study suggests a role of NGFR in limiting inflammation for repair of diseased skeletal tissues.

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.

Nerve Growth Factor Receptor Limits Inflammation to Promote Remodeling and Repair of Osteoarthritic Joints

Osteoarthritis (OA) is a painful, incurable disease affecting over 500 million people. The need for relieving OA pain is paramount but inadequately addressed, partly due to limited understandings of how pain signaling regulates non-neural tissues. Here we report that nerve growth factor receptor (NGFR) is upregulated in skeletal cells during OA and plays an essential role in the remodeling and repair of osteoarthritic joints. Specifically, NGFR is expressed in osteochondral cells but not in skeletal progenitor cells and induced by TNFα to attenuate NF-κB activation, maintaining proper BMP-SMAD1 signaling and suppressing RANKL expression. NGFR deficiency hyper-activates NF-κB in murine osteoarthritic joints, which impairs bone formation and enhances bone resorption as exemplified by a reduction in subchondral bone and osteophytes. In human OA cartilage, NGFR is also negatively associated with NF-κB activation. Together, this study uncovers a role of NGFR in limiting inflammation for repair of diseased skeletal tissues.

Distinct mast cell subpopulations within and around lymphatic vessels regulate lymph flow and progression of inflammatory-erosive arthritis in TNF-transgenic mice

Objective

Inflammatory-erosive arthritis is exacerbated by dysfunction of joint-draining popliteal lymphatic vessels (PLVs). Synovial mast cells are known to be pro-inflammatory in rheumatoid arthritis (RA). In other settings they have anti-inflammatory and tissue reparative effects. Herein, we elucidate the role of mast cells on PLV function and inflammatory-erosive arthritis in tumor necrosis factor transgenic (TNF-tg) mice that exhibit defects in PLVs commensurate with disease progression.

Methods

Whole mount immunofluorescent microscopy, toluidine blue stained histology, scanning electron microscopy, and in silico bioinformatics were performed to phenotype and quantify PLV mast cells. Ankle bone volumes were assessed by μCT, while corresponding histology quantified synovitis and osteoclasts. Near-infrared indocyanine green imaging measured lymphatic clearance as an outcome of PLV draining function. Effects of genetic MC depletion were assessed via comparison of 4.5-month-old WT, TNF-tg, MC deficient KitW-sh/W-sh (cKit-/-), and TNF-tg x cKit-/- mice. Pharmacological inhibition of mast cells was assessed by treating TNF-tg mice with placebo or cromolyn sodium (3.15mg/kg/day) for 3-weeks.

Results

PLVs are surrounded by MCT+/MCPT1+/MCPT4+ mast cells whose numbers are increased 2.8-fold in TNF-tg mice. The percentage of peri-vascular degranulating mast cells was inversely correlated with ICG clearance. A population of MCT+/MCPT1-/MCPT4- mast cells were embedded within the PLV structure. In silico single-cell RNA-seq (scRNAseq) analyses identified a population of PLV-associated mast cells (marker genes: Mcpt4, Cma1, Cpa3, Tpsb2, Kit, Fcer1a & Gata2) with enhanced TGFβ-related signaling that are phenotypically distinct from known MC subsets in the Mouse Cell Atlas. cKit-/- mice have greater lymphatic defects than TNF-tg mice with exacerbation of lymphatic dysfunction and inflammatory-erosive arthritis in TNF-tg x cKit-/- vs. TNF-Tg mice. Cromolyn sodium therapy stabilized PLV mast cells, increased TNF-induced bone loss, synovitis, and osteoclasts, and decreased ICG clearance.

Conclusions

Mast cells are required for normal lymphatic function. Genetic ablation and pharmacological inhibition of mast cells exacerbates TNF-induced inflammatory-erosive arthritis with decreased lymphatic clearance. Together, these findings support an inflammatory role of activated/degranulated peri-PLV mast cells during arthritic progression, and a homeostatic role of intra-PLV mast cells, in which loss of the latter dominantly exacerbates arthritis secondary to defects in joint-draining lymphatics, warranting investigation into specific cellular mechanisms.

The emerging importance of lymphatics in health and disease: an NIH workshop report

The lymphatic system (LS) is composed of lymphoid organs and a network of vessels that transport interstitial fluid, antigens, lipids, cholesterol, immune cells, and other materials in the body. Abnormal development or malfunction of the LS has been shown to play a key role in the pathophysiology of many disease states. Thus, improved understanding of the anatomical and molecular characteristics of the LS may provide approaches for disease prevention or treatment. Recent advances harnessing single-cell technologies, clinical imaging, discovery of biomarkers, and computational tools have led to the development of strategies to study the LS. This Review summarizes the outcomes of the NIH workshop entitled "Yet to be Charted: Lymphatic System in Health and Disease," held in September 2022, with emphasis on major areas for advancement. International experts showcased the current state of knowledge regarding the LS and highlighted remaining challenges and opportunities to advance the field.

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.

Multi-omics analysis identifies IgG2b class-switching with ALCAM-CD6 co-stimulation in joint-draining lymph nodes during advanced inflammatory-erosive arthritis

Introduction

Defective lymphatic drainage and translocation of B-cells in inflamed (Bin) joint-draining lymph node sinuses are pathogenic phenomena in patients with severe rheumatoid arthritis (RA). However, the molecular mechanisms underlying this lymphatic dysfunction remain poorly understood. Herein, we utilized multi-omic spatial and single-cell transcriptomics to evaluate altered cellular composition (including lymphatic endothelial cells, macrophages, B-cells, and T-cells) in the joint-draining lymph node sinuses and their associated phenotypic changes and cell-cell interactions during RA development using the tumor necrosis factor transgenic (TNF-Tg) mouse model.

Methods

Popliteal lymph nodes (PLNs) from wild-type (n=10) and TNF-Tg male mice with "Early" (5 to 6-months of age; n=6) and "Advanced" (>8-months of age; n=12) arthritis were harvested and processed for spatial transcriptomics. Single-cell RNA sequencing (scRNAseq) was performed in PLNs from the TNF-Tg cohorts (n=6 PLNs pooled/cohort). PLN histopathology and ELISPOT along with ankle histology and micro-CT were evaluated. Histopathology of human lymph nodes and synovia was performed for clinical correlation.

Results

Advanced PLN sinuses exhibited an increased Ighg2b/Ighm expression ratio (Early 0.5 ± 0.1 vs Advanced 1.4 ± 0.5 counts/counts; p<0.001) that significantly correlated with reduced talus bone volumes in the afferent ankle (R2 = 0.54, p<0.001). Integration of single-cell and spatial transcriptomics revealed the increased IgG2b+ plasma cells localized in MARCO+ peri-follicular medullary sinuses. A concomitant decreased Fth1 expression (Early 2.5 ± 0.74 vs Advanced 1.0 ± 0.50 counts, p<0.001) within Advanced PLN sinuses was associated with accumulation of iron-laden Prussian blue positive macrophages in lymph nodes and synovium of Advanced TNF-Tg mice, and further validated in RA clinical samples. T-cells were increased 8-fold in Advanced PLNs, and bioinformatic pathway assessment identified the interaction between ALCAM+ macrophages and CD6+ T-cells as a plausible co-stimulatory mechanism to promote IgG2b class-switching.

Discussion

Collectively, these data support a model of flare in chronic TNF-induced arthritis in which loss of lymphatic flow through affected joint-draining lymph nodes facilitates the interaction between effluxing macrophages and T-cells via ALCAM-CD6 co-stimulation, initiating IgG2b class-switching and plasma cell differentiation of the expanded Bin population. Future work is warranted to investigate immunoglobulin clonality and potential autoimmune consequences, as well as the efficacy of anti-CD6 therapy to prevent these pathogenic events.

Near-Infrared Imaging of Indocyanine Green Identifies Novel Routes of Lymphatic Drainage from Metacarpophalangeal Joints in Healthy Human Hands

Background: Collecting lymphatic vessel (CLV) dysfunction has been implicated in various diseases, including rheumatoid arthritis (RA). RA patients with active hand arthritis exhibit significantly reduced lymphatic clearance of the web spaces adjacent to the metacarpophalangeal (MCP) joints and a reduction in total and basilic-associated CLVs on the dorsal surface of the hand by near-infrared (NIR) imaging of indocyanine green (ICG). In this pilot study, we assessed direct lymphatic drainage from MCP joints and aimed to visualize the total lymphatic anatomy using novel dual-agent relaxation contrast magnetic resonance lymphography (DARC-MRL) in the upper extremity of healthy human subjects. Methods and Results: Two healthy male subjects >18 years old participated in the study. We performed NIR imaging along with conventional- or DARC-MRL following intradermal web space and intra-articular MCP joint injections. ICG (NIR) or gadolinium (Gd) (MRL) was administered to visualize the CLV anatomy of the upper extremity. Web space draining CLVs were associated with the cephalic side of the antecubital fossa, while MCP draining CLVs were localized to the basilic side of the forearm by near-infrared indocyanine green imaging. The DARC-MRL methods used in this study did not adequately nullify the contrast in the blood vessels, and limited Gd-filled CLVs were identified. Conclusion: MCP joints predominantly drain into basilic CLVs in the forearm, which may explain the reduction in basilic-associated CLVs in the hands of RA patients. Current DARC-MRL techniques show limited identification of healthy lymphatic structures, and further refinement in this technique is necessary. Clinical trial registration number: NCT04046146.

Effect of Manual Lymphatic Drainage on the Concentrations of Selected Adipokines, Cytokines, C-Reactive Protein and Parameters of Carbohydrate and Lipid Metabolism in Patients with Abnormal Body Mass Index: Focus on Markers of Obesity and Insulin Resistance

The aim of the study was to assess the impact of manual lymphatic drainage (MLD) on the parameters of carbohydrate metabolism, lipid metabolism and the level of selected adipokines and cytokines in people with abnormal body mass index (BMI). In addition, an attempt was made to assess the optimal cut-off values of serum concentrations of the biochemical parameters studied in identifying the risk of obesity and insulin resistance (IR). The study included 60 subjects who underwent 10 and 30 min long MLD sessions three times a week. The study group included 15 patients with a normal body mass index (group I; n = 15), overweight patients (group II; n = 15) and obese patients (group III; n = 10). The control group was IV; n = 20 subjects not undergoing MLD. Biochemical tests were carried out on all subjects at stage 0' (before MLD therapy) and at stage 1' (one month after MLD therapy). In the control group, the time between the sample collection at stage 0' and stage 1' was the same as in the study group. Our results showed that 10 MLD sessions may have a positive effect on the selected biochemical parameters, including insulin, 2h-PG, leptin and HOMA-IR values in normal weight and overweight patients. In addition, in the study group, the highest AUC_ROC values in identifying the risk of obesity were found for leptin (AUC_ROC = 82.79%; cut-off = 17.7 ng/mL; p = 0.00004), insulin (AUC_ROC = 81.51%; cut-off = 9.5 µIU/mL; p = 0.00009) and C-peptide (AUC_ROC = 80.68%; cut-off = 2.3 ng/mL; p = 0.0001) concentrations as well as for HOMA-IR values (AUC_ROC = 79.97%; cut-off = 1.8; p = 0.0002). When considering the risk of IR, we observed the highest diagnostic value for insulin (AUC_ROC = 93.05%; cut-off = 1.8 ng/mL; p = 0.053), which was followed by C-peptide (AUC_ROC = 89.35%; cut-off = 17.7 ng/mL; p = 0.000001), leptin (AUC_ROC = 79.76%; cut-off = 17.6 ng/mL; p = 0.0002) and total cholesterol (AUC_ROC = 77.31%; cut-off = 198 mg/dL; p = 0.0008). Our results indicate that MLD may have a positive effect on selected biochemical parameters, including insulin, 2h-PG, leptin and HOMA-IR, in normal weight and overweight patients. In addition, we successfully established optimal cut-off values for leptin in the assessment of obesity and insulin in the assessment of insulin resistance in patients with abnormal body mass index. Based on our findings, we hypothesize that MLD, when combined with caloric restriction and physical activity, may serve as an effective preventive intervention against the development of obesity and insulin resistance.

Intestinal Lymphatic Dysfunction in Kidney Disease

Kidney disease is associated with adverse consequences in many organs beyond the kidney, including the heart, lungs, brain, and intestines. The kidney-intestinal cross talk involves intestinal epithelial damage, dysbiosis, and generation of uremic toxins. Recent studies reveal that kidney injury expands the intestinal lymphatics, increases lymphatic flow, and alters the composition of mesenteric lymph. The intestinal lymphatics, like blood vessels, are a route for transporting potentially harmful substances generated by the intestines. The lymphatic architecture and actions are uniquely suited to take up and transport large macromolecules, functions that differentiate them from blood vessels, allowing them to play a distinct role in a variety of physiological and pathological processes. Here, we focus on the mechanisms by which kidney diseases result in deleterious changes in intestinal lymphatics and consider a novel paradigm of a vicious cycle of detrimental organ cross talk. This concept involves kidney injury-induced modulation of intestinal lymphatics that promotes production and distribution of harmful factors, which in turn contributes to disease progression in distant organ systems.

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.

Implementation of automated behavior metrics to evaluate voluntary wheel running effects on inflammatory-erosive arthritis and interstitial lung disease in TNF-Tg mice

BACKGROUND

Although treatment options and algorithms for rheumatoid arthritis (RA) have improved remarkably in recent decades, there continues to be no definitive cure or pharmacologic intervention with reliable long-term efficacy. For this reason, the combination of medications and healthy lifestyle modifications are essential for controlling joint disease, and extra-articular manifestations of RA, such as interstitial lung disease (ILD) and other lung pathologies, which greatly impact morbidity and mortality. Generally, exercise has been deemed beneficial in RA patients, and both patients and clinicians are motivated to incorporate effective non-pharmacologic interventions. However, there are limited evidence-based and specific exercise regimens available to support engagement in such activities for RA patients. Here, we provided the continuous opportunity for exercise to mice and implemented automated recording and quantification of wheel running behavior. This allowed us to describe the associated effects on the progression of inflammatory-erosive arthritis and ILD in the tumor necrosis factor transgenic (TNF-Tg) mouse model of RA.

METHODS

Wild-type (WT; males, n=9; females, n=9) and TNF-Tg (males, n=12; females, n=14) mice were singly housed with free access to a running wheel starting at 2 months until 5 to 5.5 months of age. Measures of running included distance, rate, length, and number of run bouts, which were derived from continuously recorded data streams collected automatically and in real-time. In vivo lung, ankle, and knee micro-computed tomography (micro-CT), along with terminal micro-CT and histology were performed to examine the association of running behaviors and disease progression relative to sedentary controls.

RESULTS

TNF-Tg males and females exhibited significantly reduced running distance, rate, length, and number of run bouts compared to WT counterparts by 5 months of age (p<0.0001). Compared to sedentary controls, running males and females showed increased aerated lung volumes (p<0.05) that were positively correlated with running distance and rate in female mice (WT: Distance, ρ=0.705/rate, ρ=0.693 (p<0.01); TNF-Tg: ρ=0.380 (p=0.06)/ρ=0.403 (p<0.05)). Talus bone volumes were significantly reduced in running versus sedentary males and negatively correlated with running distance and rate in TNF-Tg mice (male: ρ=-903/ρ=-0.865; female: ρ=-0.614/ρ=-0.594 (p<0.001)). Histopathology validated the lung and ankle micro-CT findings.

CONCLUSIONS

Implementation of automated wheel running behavior metrics allows for evaluation of longitudinal activity modifications hands-off and in real-time to relate with biomarkers of disease severity. Through such analysis, we determined that wheel running activity increases aerated lung volumes, but exacerbates inflammatory-erosive arthritis in TNF-Tg mice. To the end of a clinically relevant model, additional functional assessment of these outcomes and studies of pain behavior are warranted.

Maackia amurensis seed lectin (MASL) ameliorates articular cartilage destruction and increases movement velocity of mice with TNFα induced rheumatoid arthritis

Up to 70 million people around the world suffer from rheumatoid arthritis. Current treatment options have varied efficacy and can cause unwanted side effects. New approaches are needed to treat this condition. Sialic acid modifications on chondrocyte receptors have been associated with arthritic inflammation and joint destruction. For example, the transmembrane mucin receptor protein podoplanin (PDPN) has been identified as a functionally relevant receptor that presents extracellular sialic acid motifs. PDPN signaling promotes inflammation and invasion associated with arthritis and, therefore, has emerged as a target that can be used to inhibit arthritic inflammation. Maackia amurensis seed lectin (MASL) can target PDPN on chondrocytes to decrease inflammatory signaling cascades and reduce cartilage destruction in a lipopolysaccharide induced osteoarthritis mouse model. Here, we investigated the effects of MASL on rheumatoid arthritis progression in a TNFα transgenic (TNF-Tg) mouse model. Results from this study indicate that MASL can be administered orally to ameliorate joint malformation and increase velocity of movement exhibited by these TNF-Tg mice. These data support the consideration of MASL as a potential treatment for rheumatoid arthritis.

Persistent popliteal lymphatic muscle cell coverage defects despite amelioration of arthritis and recovery of popliteal lymphatic vessel function in TNF-Tg mice following anti-TNF therapy

While rheumatoid arthritis patients and tumor necrosis factor transgenic (TNF-Tg) mice with inflammatory-erosive arthritis display lymphatic drainage deficits, the mechanisms responsible remain unknown. As ultrastructural studies of joint-draining popliteal lymphatic vessels (PLVs) in TNF-Tg mice revealed evidence of lymphatic muscle cell (LMC) damage, we aimed to evaluate PLV-LMC coverage in TNF-Tg mice. We tested the hypothesis that alpha smooth muscle actin (αSMA)+ PLV-LMC coverage decreases with severe inflammatory-erosive arthritis, and is recovered by anti-TNF therapy facilitated by increased PLV-LMC turnover during amelioration of joint disease. TNF-Tg mice with established disease received anti-TNF monoclonal antibody (mAb) or placebo IgG isotype control mAb therapy (n = 5) for 6-weeks, while wild-type (WT) littermates (n = 8) received vehicle (PBS). Bromodeoxyuridine (BrdU) was also administered daily during the treatment period to monitor PLV-LMC turnover. Effective anti-TNF therapy was confirmed by longitudinal assessment of popliteal lymph node (PLN) volume via ultrasound, PLV contraction frequency via near-infrared imaging of indocyanine green, and ankle bone volumes via micro-computed tomography (micro-CT). Terminal knee micro-CT, and ankle and knee histology were also performed. PLVs were immunostained for αSMA and BrdU to evaluate PLV-LMC coverage and turnover, respectively, via whole-mount fluorescent microscopy. Anti-TNF therapy reduced PLN volume, increased talus and patella bone volumes, and reduced tarsal and knee synovial areas compared to placebo treated TNF-Tg mice (p < 0.05), as expected. Anti-TNF therapy also increased PLV contraction frequency at 3-weeks (from 0.81 ± 1.0 to 3.2 ± 2.0 contractions per minute, p < 0.05). However, both anti-TNF and placebo treated TNF-Tg mice exhibited significantly reduced αSMA+ PLV-LMC coverage compared to WT (p < 0.05). There was no correlation of αSMA+ PLV-LMC coverage restoration with amelioration of inflammatory-erosive arthritis. Similarly, there was no difference in PLV-LMC turnover measured by BrdU labeling between WT, TNF-Tg placebo, and TNF-Tg anti-TNF groups with an average of < 1% BrdU+ PLV-LMCs incorporated per week. Taken together these results demonstrate that PLV-LMC turnover in adult mice is limited, and that recovery of PLV function during amelioration of inflammatory-erosive arthritis occurs without restoration of αSMA+ LMC coverage. Future studies are warranted to investigate the direct and indirect effects of chronic TNF exposure, and the role of proximal inflammatory cells on PLV contractility.

Single-cell transcriptomics of popliteal lymphatic vessels and peripheral veins reveals altered lymphatic muscle and immune cell populations in the TNF-Tg arthritis model

Background

Lymphatic dysfunction exists in tumor necrosis factor transgenic (TNF-Tg) mice and rheumatoid arthritis (RA) patients. While joint-draining TNF-Tg popliteal lymphatic vessels (PLVs) have deficits in contractility during end-stage arthritis, the nature of lymphatic muscle cells (LMCs) and their TNF-altered transcriptome remain unknown. Thus, we performed single-cell RNA-sequencing (scRNAseq) on TNF-Tg LMCs in PLVs efferent to inflamed joints versus wild-type (WT) controls.

Methods

Single-cell suspensions of PLVs were sorted for smooth muscle cells (SMCs), which was validated by Cspg4-Cre;tdTomato reporter gene expression. Single-cell RNA-seq was performed on a 10x Genomics platform and analyzed using the Seurat R package. Uniform Manifold Approximation and Projections (UMAPs) and Ingenuity Pathway Analysis software were used to assess cell clusters and functional genomics in WT vs. TNF-Tg populations.

Results

Fluorescent imaging of Cspg4-Cre;tdTomato vessels demonstrated dim PLVs and strong reporter gene expression in the adjacent superficial saphenous vein, which was corroborated by flow cytometry of LMCs and vascular smooth muscle cells (VSMCs) from these vessels. Due to their unique morphology, these populations could also be readily detected by scatter analysis of cells from non-fluorescent mice. Bioinformatics analysis of flow sorted WT and TNF-Tg cells identified 20 unique cell clusters that together were 22.4% LMCs, 15.0% VSMCs, and 62.6% non-muscle cells of 8879 total cells. LMCs and M2-macrophages were decreased, while inflammatory monocytes were increased in TNF-Tg lower limb vasculature. SMC populations were defined by Cald1, Tpm1, and Pdgfrb expression and were enriched in myofibroblast-like gene expression. TNF-Tg LMCs exhibited enhanced functional genomics associated with cell death, phagocyte recruitment, and joint inflammation. Among the most prominent TNF-induced genes in SMCs were Mmp3, Cxcl12, and Ccl19, and the most downregulated genes were Zbtb16, Galnt15, and Apod.

Conclusions

Single-cell RNA-seq can be used to investigate functional genomics of lower limb vasculature in mice. Our findings confirm the inflammatory transcriptome of TNF-Tg vessels and altered gene expression in SMC populations. This study further supports a potential role of mesenchymal stromal cells in inflammatory-erosive arthritis pathogenesis, and warrants future studies to define the effects of this TNF-altered transcriptome on PLV function and joint homeostasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02730-z.

TNF-Polarized Macrophages Produce Insulin-like 6 Peptide to Stimulate Bone Formation in Rheumatoid Arthritis in Mice

The risk of osteoporosis is increased in rheumatoid arthritis (RA). Anti-tumor necrosis factor (TNF) therapy has markedly improved the outcomes of RA patients but does not improve osteoporosis in some reports. This could be a combined result of disease severity and other therapeutic agents, such as glucocorticoids that accelerate osteoporosis progression. We evaluated the effects of anti-TNF therapy on osteoporosis in an animal model of RA and explored the possible mechanisms involved. Six-week-old TNF transgenic (TNF-Tg) mice with early stage erosive arthritis were treated with TNF antibody (Ab) or control immunoglobulin (IgG) weekly for 4 weeks. We found that TNF Ab completely blocked the development of erosive arthritis in TNF-Tg mice, but only slightly increased vertebral bone mass, associated with reduction in parameters of both bone resorption and formation. Similarly, TNF Ab slightly increased trabecular bone mass in tibias of 8-month-old TNF-Tg mice with advanced erosive arthritis. Interestingly, TNFα increased osteoblast differentiation from mouse bone marrow stromal cells (BMSCs) containing large number of macrophages but not from pure mesenchymal progenitor cells (MPCs). TNFα-polarized macrophages (TPMs) did not express iNos and Arginase 1, typical markers of inflammatory and resident macrophages. Interestingly, TPMs stimulated osteoblast differentiation, unlike resident and inflammatory macrophages polarized by IL-4 and interferon-λ, respectively. RNA-seq analysis indicated that TPMs produced several anabolic factors, including Jagged1 and insulin like 6 (INSL6). Importantly, inhibition of either Jagged1 or INSL6 blocked TNFα-induced osteoblast differentiation. Furthermore, INSL6 Ab significantly decreased the expansion of TNF-induced MPCs in BMSCs, and anti-TNF Ab reduced INSL6 expression by macrophages in vitro and in TNF-Tg mice in vivo. We conclude that TPMs produce INSL6 to stimulate bone formation and anti-TNF Ab blocks not only enhanced bone resorption but also the anabolic effect of TPMs on bone, limiting its effect to increase bone mass in this model of RA. © 2021 American Society for Bone and Mineral Research (ASBMR).

Spike protein multiorgan tropism suppressed by antibodies targeting SARS-CoV-2

While there is SARS-CoV-2 multiorgan tropism in severely infected COVID-19 patients, it's unclear if this occurs in healthy young individuals. In addition, for antibodies that target the spike protein (SP), it's unclear if these reduce SARS-CoV-2/SP multiorgan tropism equally. We used fluorescently labeled SP-NIRF to study viral behavior, using an in vivo dynamic imaging system and ex in vivo tissue analysis, in young mice. We found a SP body-wide biodistribution followed by a slow regional elimination, except for the liver, which showed an accumulation. SP uptake was highest for the lungs, and this was followed by kidney, heart and liver, but, unlike the choroid plexus, it was not detected in the brain parenchyma or CSF. Thus, the brain vascular barriers were effective in restricting the entry of SP into brain parenchyma in young healthy mice. While both anti-ACE2 and anti-SP antibodies suppressed SP biodistribution and organ uptake, anti-SP antibody was more effective. By extension, our data support the efficacy of these antibodies on SARS-CoV-2 multiorgan tropism, which could determine COVID-19 organ-specific outcomes.

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.

Adipose Tissue and Biological Factors. Possible Link between Lymphatic System Dysfunction and Obesity

The World Health Organization (WHO) has recognised obesity as one of the top ten threats to human health. Obesity is not only a state of abnormally increased adipose tissue in the body, but also of an increased release of biologically active metabolites. Moreover, obesity predisposes the development of metabolic syndrome and increases the incidence of type 2 diabetes (T2DM), increases the risk of developing insulin resistance, atherosclerosis, ischemic heart disease, polycystic ovary syndrome, hypertension and cancer. The lymphatic system is a one-directional network of thin-walled capillaries and larger vessels covered by a continuous layer of endothelial cells that provides a unidirectional conduit to return filtered arterial and tissue metabolites towards the venous circulation. Recent studies have shown that obesity can markedly impair lymphatic function. Conversely, dysfunction in the lymphatic system may also be involved in the pathogenesis of obesity. This review highlights the important findings regarding obesity related to lymphatic system dysfunction, including clinical implications and experimental studies. Moreover, we present the role of biological factors in the pathophysiology of the lymphatic system and we propose the possibility of a therapy supporting the function of the lymphatic system in the course of obesity.

Lymphatic Contractile Function: A Comprehensive Review of Drug Effects and Potential Clinical Application

BACKGROUND

The lymphatic system and the cardiovascular system work together to maintain body fluid homeostasis. Despite that, the lymphatic system has been relatively neglected as a potential drug target and a source of adverse effects from cardiovascular drugs. Like the heart, the lymphatic vessels undergo phasic contractions to promote lymph flow against a pressure gradient. Dysfunction or failure of the lymphatic pump results in fluid imbalance and tissue oedema. While this can due to drug effects, it is also a feature of breast cancer-associated lymphoedema, chronic venous insufficiency, congestive heart failure and acute systemic inflammation. There are currently no specific drug treatments for lymphatic pump dysfunction in clinical use despite the wealth of data from pre-clinical studies.

AIM

To identify (1) drugs with direct effects on lymphatic tonic and phasic contractions with potential for clinical application, and (2) drugs in current clinical use that have a positive or negative side effect on lymphatic function.

METHODS

We comprehensively reviewed all studies that tested the direct effect of a drug on the contractile function of lymphatic vessels.

RESULTS

Of the 208 drugs identified from 193 studies, about a quarter had only stimulatory effects on lymphatic tone, contraction frequency and/or contraction amplitude. Of FDA-approved drugs, there were 14 that increased lymphatic phasic contractile function. The most frequently used class of drug with inhibitory effects on lymphatic pump function were the calcium channels blockers.

CONCLUSION

This review highlights the opportunity for specific drug treatments of lymphatic dysfunction in various disease states and for avoiding adverse drug effects on lymphatic contractile function.

Altered Lymphatic Vessel Anatomy and Markedly Diminished Lymph Clearance in Affected Hands of Patients With Active Rheumatoid Arthritis

OBJECTIVE

To assess differences between lymphatic function in the affected hands of rheumatoid arthritis (RA) patients with active synovitis and that of healthy controls, using indocyanine green (ICG) dye and near-infrared (NIR) imaging.

METHODS

NIR imaging of the hands of 8 patients with active RA and 13 healthy controls was performed following web space injection of 0.1 ml of 100 μM ICG. The percentage of ICG retention in the web spaces was determined by NIR imaging at baseline and at 7 days (±1 day) after the initial injections; image analysis provided contraction frequency. ICG+ lymphatic vessel (LV) length and branching architecture were assessed.

RESULTS

Retention of ICG in RA hands was higher compared to controls (P < 0.01). The average contraction frequency of ICG+ LVs in RA patients and in controls did not differ (mean ± SD 0.53 ± 0.39 contractions/minute versus 0.51 ± 0.35 contractions/minute). Total ICG+ LV length in RA hands was lower compared to healthy controls (58.3 ± 15.0 cm versus 71.4 ± 16.1 cm; P < 0.001), concomitant with a decrease in the number of ICG+ basilic LVs in the hands of RA patients (P < 0.05).

CONCLUSION

Lymphatic drainage in the hands of RA patients with active disease was reduced compared to controls. This reduction was associated with a decrease in total length of ICG+ LVs on the dorsal surface of the hands, which continued to contract at a similar rate to that observed in controls. These findings provide a plausible mechanism for exacerbation of synovitis and joint damage, specifically the accumulation and retention of inflammatory cells and catabolic factors in RA joints due to impaired efferent lymphatic flow. NIR/ICG imaging of RA hands is feasible and warrants formal investigation as a primary outcome measure for arthritis disease severity and/or persistence in future clinical trials.

Lineage tracing reveals evidence of a popliteal lymphatic muscle progenitor cell that is distinct from skeletal and vascular muscle progenitors

Loss of popliteal lymphatic vessel (PLV) contractions, which is associated with damage to lymphatic muscle cells (LMCs), is a biomarker of disease progression in mice with inflammatory arthritis. Currently, the nature of LMC progenitors has yet to be formally described. Thus, we aimed to characterize the progenitors of PLV-LMCs during murine development, towards rational therapies that target their proliferation, recruitment, and differentiation onto PLVs. Since LMCs have been described as a hybrid phenotype of striated and vascular smooth muscle cells (VSMCs), we performed lineage tracing studies in mice to further clarify this enigma by investigating LMC progenitor contribution to PLVs in neonatal mice. PLVs from Cre-tdTomato reporter mice specific for progenitors of skeletal myocytes (Pax7⁺ and MyoD⁺) and VSMCs (Prrx1⁺ and NG2⁺) were analyzed via whole mount immunofluorescent microscopy. The results showed that PLV-LMCs do not derive from skeletal muscle progenitors. Rather, PLV-LMCs originate from Pax7^-/MyoD^-/Prrx1⁺/NG2⁺ progenitors similar to VSMCs prior to postnatal day 10 (P10), and from a previously unknown Pax7^-/MyoD^-/Prrx1⁺/NG2^- muscle progenitor pathway during development after P10. Future studies of these LMC progenitors during maintenance and repair of PLVs, along with their function in other lymphatic beds, are warranted.

TNF-Induced Interstitial Lung Disease in a Murine Arthritis Model: Accumulation of Activated Monocytes, Conventional Dendritic Cells, and CD21+/CD23- B Cell Follicles Is Prevented with Anti-TNF Therapy

Interstitial lung disease (ILD) is a well-known extra-articular manifestation of rheumatoid arthritis (RA). RA-associated ILD (RA-ILD) exists on a wide spectrum, with variable levels of inflammatory and fibrotic activity, although all subtypes are regarded as irreversible pathologic conditions. In both articular and pulmonary manifestations, TNF is a significant pathogenic factor. Whereas anti-TNF therapy alleviates joint pathologic conditions, it exacerbates fibrotic RA-ILD. The TNF-transgenic (TNF-Tg) murine model of RA develops both inflammatory arthritis and an ILD that mimics a cellular nonspecific interstitial pneumonia pattern dominated by an interstitial accumulation of inflammatory cells with minimal-to-absent fibrosis. Given the model's potential to elucidate the genesis of inflammatory RA-ILD, we aim to achieve the following: 1) characterize the cellular accumulations in TNF-Tg lungs, and 2) assess the reversibility of inflammatory ILD following anti-TNF therapy known to resolve TNF-Tg inflammatory arthritis. TNF-Tg mice with established disease were randomized to anti-TNF or placebo therapy and evaluated with imaging, histology, and flow cytometric analyses, together with wild-type controls. Flow cytometry of TNF-Tg versus wild-type lungs revealed significant increases in activated monocytes, conventional dendritic cells, and CD21+/CD23- B cells that are phenotypically distinct from the B cells in inflamed nodes, which are known to accumulate in joint-draining lymph nodes. In contrast to human RA-ILD, anti-TNF treatment significantly alleviated both joint and lung inflammation. These results identify a potential role for activated monocytes, conventional dendritic cells, and CD21+/CD23- B cells in the genesis of RA-ILD, which exist in a previously unknown, reversible, prefibrotic stage of the disease.

iNOS dependent and independent phases of lymph node expansion in mice with TNF-induced inflammatory-erosive arthritis

Introduction

A pivotal effect of lymphatic vessel (LV) function in joint homeostasis was identified in the tumor necrosis factor-transgenic (TNF-Tg) mouse model of rheumatoid arthritis (RA). Specifically, loss of LV contractions is associated with progressive synovitis and erosions. Furthermore, draining lymph node expansion is a biomarker of arthritic progression, and both macrophages and lymphatic endothelial cells express inducible nitric oxide synthase (iNOS), which disrupts LV contraction and transport of immune cells to the draining lymph nodes. Therefore, to directly assess these relationships, we tested the hypothesis that TNF-Tg mice with global genetic ablation of iNOS (iNOS^−/−) will show delayed draining lymph node expansion, maintained LV contractions, and decreased synovitis and erosions.

Method

iNOS^−/−× TNF-Tg female and male mice, and control littermates (iNOS^−/−, TNF-Tg, and WT), were examined with (1) ultrasound to determine popliteal lymph node (PLN) volume and (2) near-infrared imaging (NIR) to assess popliteal LV contraction frequency, and differences between genotypes were assessed at 3, 4, 5, and 6 months of age. Knees and PLN were harvested at 4 months in females and 6 months in males, to assess synovitis, bone erosions, and cellular accumulation in PLN sinuses via histology.

Results

Initially, an increase in PLN volume was observed for both female and male iNOS^−/−× TNF-Tg and TNF-Tg compared to their WT and iNOS^−/− counterparts at 2 and 3 months, respectively. Subsequently, TNF-Tg PLNs continue to increase in volume, while iNOS^−/−× TNF-Tg did not increase in volume from the initial timepoints. WT and iNOS^−/− PLN volume was unchanged throughout the experiment. LV contraction frequency was increased at 4 months in females and 5 months in males, in the iNOS^−/−× TNF-Tg mice compared to the TNF-Tg. Synovitis and erosions were moderately reduced in iNOS^−/−× TNF-Tg versus TNF-Tg knees in females, while no differences in knee pathology were observed in males.

Conclusions

Genetic iNOS ablation maintains draining lymph node volume and LV function during TNF-induced inflammatory arthritis and is associated with moderately decreased joint inflammation and damage.

Cardiac lymphatics in health and disease

The lymphatic vasculature, which accompanies the blood vasculature in most organs, is indispensable in the maintenance of tissue fluid homeostasis, immune cell trafficking, and nutritional lipid uptake and transport, as well as in reverse cholesterol transport. In this Review, we discuss the physiological role of the lymphatic system in the heart in the maintenance of cardiac health and describe alterations in lymphatic structure and function that occur in cardiovascular pathology, including atherosclerosis and myocardial infarction. We also briefly discuss the role that immune cells might have in the regulation of lymphatic growth (lymphangiogenesis) and function. Finally, we provide examples of how the cardiac lymphatics can be targeted therapeutically to restore lymphatic drainage in the heart to limit myocardial oedema and chronic inflammation.

Lymphatic Function in Autoimmune Diseases

Lymphatic vessels are critical for clearing fluid and inflammatory cells from inflamed tissues and also have roles in immune tolerance. Given the functional association of the lymphatics with the immune system, lymphatic dysfunction may contribute to the pathophysiology of rheumatic autoimmune diseases. Here we review the current understanding of the role of lymphatics in the autoimmune diseases rheumatoid arthritis, scleroderma, lupus, and dermatomyositis and consider the possibility that manual therapies such as massage and acupuncture may be useful in improving lymphatic function in autoimmune diseases.

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.

Attenuated Joint Tissue Damage Associated With Improved Synovial Lymphatic Function Following Treatment With Bortezomib in a Mouse Model of Experimental Posttraumatic Osteoarthritis

OBJECTIVE

To investigate the roles of the synovial lymphatic system in the severity and progression of joint tissue damage and functional responses of synovial lymphatic endothelial cells (LECs) to macrophage subsets, and to evaluate the therapeutic potential of the proteasome inhibitor bortezomib (BTZ) in a mouse model of experimental posttraumatic osteoarthritis (OA).

METHODS

C57BL/6J wild-type mice received a meniscal ligamentous injury to induce posttraumatic knee OA. Lymphangiogenesis was blocked by a vascular endothelial growth factor receptor 3 (VEGFR-3) neutralizing antibody. Synovial lymphatic drainage was examined by near-infrared imaging. Joint damage was assessed by histology. RNA-sequencing and pathway analyses were applied to synovial LECs. Macrophage subsets in the mouse synovium were identified by flow cytometry and immunofluorescence staining. M1 and M2 macrophages were induced from mouse bone marrow cells, and their effects on LECs were examined in cocultures in the presence or absence of BTZ. The effects of BTZ on joint damage, LEC inflammation, and synovial lymphatic drainage were examined.

RESULTS

Injection of a VEGFR-3 neutralizing antibody into the joints of mice with posttraumatic knee OA reduced synovial lymphatic drainage and accelerated joint tissue damage. Synovial LECs from the mouse OA joints had dysregulated inflammatory pathways and expressed high levels of inflammatory genes. The number of M1 macrophages was increased in the knee joints of mice with posttraumatic OA, thereby promoting the expression of inflammatory genes by LECs; this effect was blocked by BTZ. Treatment with BTZ decreased cartilage loss, reduced the expression of inflammatory genes by LECs, and improved lymphatic drainage in the knee joints of mice with posttraumatic OA.

CONCLUSION

Experimental posttraumatic knee OA is associated with decreased synovial lymphatic drainage, increased numbers of M1 macrophages, and enhanced inflammatory gene expression by LECs, all of which was improved by treatment with BTZ. Intraarticular administration of BTZ may represent a new therapy for the restoration of synovial lymphatic function in subjects with posttraumatic knee OA.

Role of simvastatin in tumor lymphangiogenesis and lymph node metastasis

Lymphangiogenesis plays a crucial role in promoting cancer metastasis to sentinel lymph nodes (LNs) and beyond. Increasing data have shown that simvastatin, a cholesterol-lowering medication for the prevention of cardiovascular diseases, is involved in tumor growth and dissemination, and endothelial functions. This study aimed to investigate the potential effect of simvastatin on lymphatic formation and LN metastasis. Tumor models were established by subcutaneous injection of B16-F10 melanoma cells into mouse hind footpads. Simvastatin was administered (0.2 µg/g, intraperitoneal injection, IP) every other day for a total of eight times. Tissue samples were removed and examined by immunohistochemical staining and reverse transcription-polymerase chain reaction (RT-PCR) techniques. The lymphatics of LN, skin, liver, and lung exhibited morphological changes, and LN weight and metastatic area of the tumor group treated with simvastatin was lower than that of the untreated tumor group. Analysis of lymphatic size, area fraction, and lymphatic vessel density showed tissue specificity and variation to melanoma carcinogenesis in the simvastatin-treated group compared with the untreated group. In addition, LNs and cutaneous tissues showed altered expression of lymphangiogenic factors and inflammatory cytokines such as VEGF-A/-C/-D and TNF-α. These findings indicated that simvastatin may modify lymphangiogenesis and tumor progression in malignant melanoma.

Fabrication of a triptolide-loaded and poly-γ-glutamic acid-based amphiphilic nanoparticle for the treatment of rheumatoid arthritis

Triptolide (TP) exhibits immunosuppressive, cartilage-protective and anti-inflammatory effects in rheumatoid arthritis. However, the toxicity of TP limits its widespread use. To decrease the toxic effects, we developed a novel nano-drug carrier system containing TP using poly-γ-glutamic acid-grafted di-tert-butyl L-aspartate hydrochloride (PAT). PAT had an average diameter of 79±18 nm, a narrow polydispersity index (0.18), a strong zeta potential (−32 mV) and a high drug encapsulation efficiency (EE₁=48.6%) and loading capacity (EE₂=19.2%), and exhibited controlled release (t_1/2=29 h). The MTT assay and flow cytometry results indicated that PAT could decrease toxicity and apoptosis induced by free TP on RAW264.7 cells. PAT decreased lipopolysaccharides/interferon γ-induced cytokines expression of macrophage (P<0.05). In vivo, PAT accumulated at inflammatory joints, improved the survival rate and had fewer side effects on tumor necrosis factor α transgenic mice, compared to TP. The blood biochemical indexes revealed that PAT did not cause much damage to the kidney (urea nitrogen and creatinine) and liver (alanine aminotransferase and aspartate aminotransferase). In addition, PAT reduced inflammatory synovial tissue area (P<0.05), cartilage loss (P<0.05), tartrate-resistant acid phosphatase-positive osteoclast area (P<0.05) and bone erosion (P<0.05) in both knee and ankle joints, and showed similar beneficial effect as free TP. In summary, our newly formed nanoparticle, PAT, can reduce the toxicity and guarantee the efficacy of TP, which represents an effective drug candidate for RA with low adverse side effect.

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.

Lymphatic delivery of etanercept via nanotopography improves response to collagen-induced arthritis

Background

Evidence suggests lymphatic function mediates local rheumatoid arthritis (RA) flares. Yet biologics that target the immune system are dosed systemically via the subcutaneous (SC) administration route, thereby inefficiently reaching local lymphatic compartments. Nanotopography has previously been shown to disrupt tight cellular junctions, potentially enhancing local lymphatic delivery and potentially improving overall therapeutic efficacy.

Method

We first characterized nanotopography (SOFUSA™) delivery of an anti-TNF drug, etanercept, by comparing pharmacokinetic profiles to those obtained by conventional SC, intravenous (IV), and intradermal (ID) routes of administration, and assessed uptake of radiolabeled etanercept in draining lymph nodes (LNs) in single dosing studies. We then compared etanercept efficacy in a progressive rat model of collagen-induced arthritis (CIA), administered systemically via SC route of administration; via the regional lymphatics through ID delivery; or through a nanotopography (SOFUSA™) device at 10, 12, and 14 days post CIA induction. Measurements of hind limb swelling and near-infrared fluorescence (NIRF) imaging of afferent lymph pumping function and reflux were conducted on days 11, 13, and 18 post CIA induction and compared to untreated CIA animals. Univariate and multivariate analysis of variance were used to compare the group differences for percentage swelling and lymphatic contractile activity.

Results

Even though all three modes of administration delivered an equal amount of etanercept, SOFUSA™ delivery resulted in increased lymphatic pumping and significantly reduced swelling as compared to untreated, ID, and SC groups. Pharmacokinetic profiles in serum and LN uptake studies showed that using the nanotopography device resulted in the greatest uptake and retention in draining LNs.

Conclusions

Locoregional lymphatic delivery of biologics that target the immune system may have more favorable pharmacodynamics than SC or IV administration. Nanotopography may provide a more efficient method for delivery of anti-TNF drugs to reverse impairment of lymphatic function and reduce swelling associated with RA flares.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1323-z) contains supplementary material, which is available to authorized users.