Lymphatic Endothelial Cells Produce M-CSF, Causing Massive Bone Loss in Mice

Reduced expression of semaphorin 3A in osteoclasts causes lymphatic expansion in a Gorham-Stout disease (GSD) mouse model

Gorham-Stout disease (GSD) is a sporadic chronic disease characterized by progressive bone dissolution, absorption, and disappearance along with lymphatic vessel infiltration in bone-marrow cavities. Although the osteolytic mechanism of GSD has been widely studied, the cause of lymphatic hyperplasia in GSD is rarely investigated. In this study, by comparing the RNA expression profile of osteoclasts (OCs) with that of OC precursors (OCPs) by RNA sequencing, we identified a new factor, semaphorin 3A (Sema3A), which is an osteoprotective factor involved in the lymphatic expansion of GSD. Compared to OCPs, OCs enhanced the growth, migration, and tube formation of lymphatic endothelial cells (LECs), in which the expression of Sema3A is low compared to that in OCPs. In the presence of recombinant Sema3A, the growth, migration, and tube formation of LECs were inhibited, further confirming the inhibitory effect of Sema3A on LECs in vitro. Using an LEC-induced GSD mouse model, the effect of Sema3A was examined by injecting lentivirus-expressing Sema3A into the tibiae in vivo. We found that the overexpression of Sema3A in tibiae suppressed the expansion of LECs and alleviated bone loss, whereas the injection of lentivirus expressing Sema3A short hairpin RNA (shRNA) into the tibiae caused GSD-like phenotypes. Histological staining further demonstrated that OCs decreased and osteocalcin increased after Sema3A lentiviral treatment, compared with the control. Based on the above results, we propose that reduced Sema3A in OCs is one of the mechanisms contributing to the pathogeneses of GSD and that expressing Sema3A represents a new approach for the treatment of GSD.

CSF-1 and Notch signaling cooperate in macrophage instruction and tissue repair during peripheral limb ischemia

Ischemia causes an inflammatory response featuring monocyte-derived macrophages (MF) involved in angiogenesis and tissue repair. Angiogenesis and ischemic macrophage differentiation are regulated by Notch signaling via Notch ligand Delta-like 1 (Dll1). Colony stimulating factor 1 (CSF-1) is an essential MF lineage factor, but its role in ischemic macrophage development and the interaction with Notch signaling is so far unclear. Using a mouse model of hind limb ischemia with CSF-1 inhibitor studies and Dll1 heterozygous mice we show that CSF-1 is induced in the ischemic niche by a subpopulation of stromal cells expressing podoplanin, which was paralleled by the development of ischemic macrophages. Inhibition of CSF-1 signaling with small molecules or blocking antibodies impaired macrophage differentiation but prolonged the inflammatory response, resulting in impaired perfusion recovery and tissue regeneration. Yet, despite high levels of CSF-1, macrophage maturation and perfusion recovery were impaired in mice with Dll1 haploinsufficiency, while inflammation was exaggerated. In vitro, CSF-1 was not sufficient to induce full MF differentiation from donor monocytes in the absence of recombinant DLL1, while the presence of DLL1 in a dose-dependent manner stimulated MF differentiation in combination with CSF-1. Thus, CSF-1 is an ischemic niche factor that cooperates with Notch signaling in a non-redundant fashion to instruct macrophage cell fate and maturation, which is required for ischemic perfusion recovery and tissue repair.

The molecular mechanism of Gorham syndrome: an update

Gorham syndrome, also known as "vanishing osteopathy" and "invasive hemangiomatosis," is a rare clinical syndrome whose etiology is unknown and can invade the whole-body skeleton. At present, more than 300 cases have been reported at home and abroad, usually manifesting as spontaneous chronic osteolysis with no periosteal reaction at the lysis site and occult onset, often with fractures, scoliosis, chylothorax, etc. When waiting for medical treatment, the condition is serious, and the prognosis is poor. At present, there is no effective treatment. The main pathological manifestations of Gorham syndrome are the non-neoplastic abnormal proliferation of lymphatic vessels or blood vessels and osteolysis caused by osteoclast proliferation or increased activity. At present, there is no unified conclusion regarding Gorham syndrome's pathogenesis. This paper starts with the two most studied osteolysis methods at present, osteoclast osteolysis and osteolysis caused by vascular and lymphatic proliferation and summarizes the corresponding most possible molecular mechanisms in recent years to provide more ideas for Gorham syndrome treatment.

Galectin-8 involves in arthritic condylar bone loss via podoplanin/AKT/ERK axis-mediated inflammatory lymphangiogenesis

OBJECTIVE

The lymphatic system plays a crucial role in the maintenance of tissue fluid homeostasis and the immunological response to inflammation. Galectin-8 (Gal-8) regulates pathological lymphangiogenesis but the effects of which on inflammation-related condylar bone loss in temporomandibular joint (TMJ) have not been well studied.

DESIGN

We used TNFα-transgenic (TNF^TG) mice and their wildtype (WT) littermates to compare their inflammatory phenotype in TMJs. Next, lymphatic endothelial cells (LECs) were used to examine the effects of which on osteoclast formation, pro-inflammatory factor expression, and inflammatory lymphangiogenesis with or without thiodigalactoside (TDG, a Gal-8 inhibitor) treatment. At last, two murine models (TNF^TG arthritic model and forced mouth opening model) were used to explore TDG as a potential drug for the treatment of inflammation-related condylar bone loss.

RESULTS

In comparison to WT mice, lymphatic areas of lymphatic vessel endothelial receptor 1 (LYVE1)⁺/podoplanin (PDPN)⁺ and Gal-8⁺/PDPN⁺, TRAP-positive osteoclast number, and condylar bone loss are increased in TNF^TG mice. Inhibition of Gal-8 in LECs by TDG, reduces TNFα-induced osteoclast formation, pro-inflammatory factor expression, and inflammatory lymphangiogenesis. In addition, Gal-8 promotes TNFα-activated AKT/ERK/NF-κB pathways by binding to PDPN. Finally, the administration of TDG attenuates inflammatory lymphangiogenesis, inhibits osteoclast activity, and reduces condylar bone loss in TNF^TG arthritic mice and forced mouth opening mice.

CONCLUSIONS

Our findings reveal the important role of Gal-8-promoted pathological lymphangiogenesis in inflammation-related condylar bone loss.

Difficult Therapeutic Decisions in Gorham-Stout Disease-Case Report and Review of the Literature

Gorham-Stout disease (GSD) is a very rare, life-threatening condition characterized by the proliferation of lymphatic vessels and osteolysis. Unfortunately, no standard treatment has been determined for management of GSD. The available therapies are not equally effective and carry substantial side-effects. We report a 42-year-old female with GSD manifested in multifocal osteolysis and chronic chylothorax and ascites. The combined treatment with sirolimus and zoledronic acid due to its synergism of action was introduced. To our knowledge, this is the first Polish case report of adult patients with Gorham-Stout disease.

Gorham-Stout disease, a diagnosis of exclusion

Gorham-Stout disease (GSD) also known as vanishing bone disease is an idiopathic and rare condition characterized by gross and progressive bone loss along with excessive growth of vascular and lymphatic tissue. Very little is known about the pathogenesis of GSD, which makes the diagnosis challenging and often diagnosed by elimination. We report a case of GSD in a 41-year-old male patient. He presented with bone pain and initial imaging showed widespread osteolytic lesions in the cervical and mid thoracic spine, ribs, sternum, clavicles, scapula, and humerus. Two percutaneous bone biopsies were performed, followed by an open spine biopsy of the lumber 2 spinous process for histological examination. Unfortunately, no diagnosis was reached. Although, he was treated symptomatically, he kept enduring pain and presented again after 7 months. His laboratory values were out of the normal range which prompted thorough investigations. New imaging and bone biopsy revealed multiple osteolytic lesions and vascular lesion with cavernous morphology respectively. GSD was diagnosed after ruling out a neoplastic process and confirming the cavernous morphology with immunohistochemical stain. He was treated symptomatically with immunomodulators, bisphosphonates, and supplements. Patient was counseled to see the specialist regularly. This case will help to increase familiarity and shed insights in the diagnosis of GSD.

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.

The importance of computed tomography (CT) scans in the early diagnosis of Gorham-Stout Disease - A case report

Gorham Stout disease (GSD) or vanishing bone disease is an infrequent entity in clinical practice characterized by gross and progressive bone loss along with excessive growth of vascular and lymphatic tissue. Very little is known about the pathogenesis of GSD, which makes the diagnosis challenging. Due to the rarity of the disease, no treatment guidelines have been created yet. We report a case of GSD in a 53-year-old male patient. He presented with bone pain and initial imaging showed widespread osteolytic lesions in the cervical and mid thoracic spine, ribs, sternum, clavicles, scapula and humerus. Two percutaneous bone biopsies were performed, followed by an open spine biopsy of the L2 spinous processes for histological examination. Unfortunately, no diagnosis was established. Although, he was treated symptomatically, he kept enduring pain and presented again after seven months. His laboratory values were out of the normal range which prompted thorough investigations. New imaging and bone biopsy revealed multiple osteolytic lesions and vascular lesions with cavernous morphology. GSD was diagnosed after ruling out a neoplastic process and confirming the cavernous morphology with immunohistochemical stain. He was treated symptomatically with immunomodulators, bisphosphonates and supplements. Regular follow-up with a specialist was recommended. We hope this case will raise awareness of GSD in common clinical practice and shed some insight on its clinical presentation and the role CT and other imaging modalities play in the diagnosis of GSD.

Arginine induces protein self-assembly into nanofibers for triggering osteogenic differentiation of stem cells

Although silk proteins are considered promising in building a scaffold for tissue engineering, one of the silk proteins, Bombyx mori silk sericin (BS), has limited processability in producing nanofibrous scaffolds because its surface charge anisotropy promotes gelation instead. To overcome this daunting challenge, we developed a mild and simple procedure for assembling BS into nanofibers and nanofibrous scaffolds. Briefly, arginine was added to the aqueous BS solution to reduce the negative charge of BS, thereby inducing BS to self-assemble into nanofibers in the solution. Circular dichroism (CD) and Fourier transform infrared (FT-IR) spectra showed that arginine promoted the formation of β-sheet conformation in BS and increased its thermal stability. Furthermore, the arginine-induced BS nanofiber solution could be casted into scaffolds made of abundant network-like nanofibrous structures. The BS scaffolds promoted cell adhesion and growth and stimulated osteogenic differentiation of the bone marrow mesenchymal stem cells (BMSCs) in the absence of differentiation inducers in culture media. Our study presents a new strategy for assembling proteins into osteogenic nanofibrous scaffolds for inducing stem cell differentiation in regenerative medicine.

The endothelium-bone axis in development, homeostasis and bone and joint disease

Blood vessels form a versatile transport network that is best known for its critical roles in processes such as tissue oxygenation, metabolism and immune surveillance. The vasculature also provides local, often organ-specific, molecular signals that control the behaviour of other cell types in their vicinity during development, homeostasis and regeneration, and also in disease processes. In the skeletal system, the local vasculature is actively involved in both bone formation and resorption. In addition, blood vessels participate in inflammatory processes and contribute to the pathogenesis of diseases that affect the joints, such as rheumatoid arthritis and osteoarthritis. This Review summarizes the current understanding of the architecture, angiogenic growth and functional properties of the bone vasculature. The effects of ageing and pathological conditions, including arthritis and osteoporosis, are also discussed.

Morin attenuates osteoclast formation and function by suppressing the NF-κB, MAPK and calcium signalling pathways

Morin is a natural compound isolated from moraceae family members and has been reported to possess a range of pharmacological activities. However, the effects of morin on bone-associated disorders and the potential mechanism remain unknown. In this study, we investigated the anti-osteoclastogenic effect of morin in vitro and the potential therapeutic effects on ovariectomy (OVX)-induced osteoporosis in vivo. In vitro, by using a bone marrow macrophage-derived osteoclast culture system, we determined that morin attenuated receptor activator of nuclear factor (NF)-κB ligand (RANKL)-induced osteoclast formation via the inhibition of the mitogen-activated protein kinase (MAPK), NF-κB and calcium pathways. In addition, the subsequent expression of nuclear factor of activated T cells c1 (NFATc1) and c-fos was significantly suppressed by morin. In addition, NFATc1 downregulation led to the reduced expression of osteoclastogenesis-related marker genes, such as V-ATPase-d2 and Integrin β3. In vivo, results provided that morin could effectively attenuate OVX-induced bone loss in C57BL/6 mice. In conclusion, our results demonstrated that morin suppressed RANKL-induced osteoclastogenesis via the NF-κB, MAPK and calcium pathways, in addition, its function of preventing OVX-induced bone loss in vivo, which suggested that morin may be a potential therapeutic agent for postmenopausal osteoporosis treatment.

Lymphatic Malformations: Genetics, Mechanisms and Therapeutic Strategies

Lymphatic vessels maintain tissue fluid homeostasis by returning to blood circulation interstitial fluid that has extravasated from the blood capillaries. They provide a trafficking route for cells of the immune system, thus critically contributing to immune surveillance. Developmental or functional defects in the lymphatic vessels, their obstruction or damage, lead to accumulation of fluid in tissues, resulting in lymphedema. Here we discuss developmental lymphatic anomalies called lymphatic malformations and complex lymphatic anomalies that manifest as localized or multifocal lesions of the lymphatic vasculature, respectively. They are rare diseases that are caused mostly by somatic mutations and can present with variable symptoms based upon the size and location of the lesions composed of fluid-filled cisterns or channels. Substantial progress has been made recently in understanding the molecular basis of their pathogenesis through the identification of their genetic causes, combined with the elucidation of the underlying mechanisms in animal disease models and patient-derived lymphatic endothelial cells. Most of the solitary somatic mutations that cause lymphatic malformations and complex lymphatic anomalies occur in genes that encode components of oncogenic growth factor signal transduction pathways. This has led to successful repurposing of some targeted cancer therapeutics to the treatment of lymphatic malformations and complex lymphatic anomalies. Apart from the mutations that act as lymphatic endothelial cell-autonomous drivers of these anomalies, current evidence points to superimposed paracrine mechanisms that critically contribute to disease pathogenesis and thus provide additional targets for therapeutic intervention. Here, we review these advances and discuss new treatment strategies that are based on the recently identified molecular pathways.

Lymphatic muscle cells contribute to dysfunction of the synovial lymphatic system in inflammatory arthritis in mice

BACKGROUND

Our previous studies reveal that impaired draining function of the synovial lymphatic vessel (LV) contributes to the pathogenesis of inflammatory arthritis, but the cellular and molecular mechanisms involved are not fully understood.

OBJECTIVE

To investigate the involvement of lymphatic muscle cells (LMCs) in mediating impaired LV function in inflammatory arthritis.

METHODS

TNF transgenic (TNF-Tg) arthritic mice were used. The structure and function of the LVs that drained the hind limbs were examined by whole-mount immunofluorescence staining, electron microscopy, and near-infrared lymphatic imaging. Primary LMCs were treated with TNF, and the changes in proliferation, apoptosis, and functional gene expression were assessed. The roles of the herbal drug, Panax notoginseng saponins (PNS), in arthritis and LVs were studied.

RESULTS

TNF-Tg mice developed ankle arthritis with age, which was associated with abnormalities of LVs: (1) dilated capillary LVs with few branch points, (2) mature LVs with reduced LMC coverage and draining function, and (3) degenerative and apoptotic appearance of LMCs. TNF caused LMC apoptosis, reduced expression of muscle functional genes, and promoted the production of nitric oxide (NO) by lymphatic endothelial cells (LECs). PNS attenuated arthritis, restored LMC coverage and draining function of mature LVs, inhibited TNF-mediated NO expression, and reduced LMC apoptosis.

CONCLUSION

The impaired draining function of LVs in TNF-Tg mice involves LMC apoptosis. TNF promotes LMC death directly and indirectly via NO production by LECs. PNS attenuates arthritis, improves LVs, and prevents TNF-induced LMC apoptosis by inhibiting NO production of LECs. LMCs contribute to the dysfunction of synovial LVs in inflammatory arthritis.

Insights into the mechanism of vascular endothelial cells on bone biology

In the skeletal system, blood vessels not only function as a conduit system for transporting gases, nutrients, metabolic waste, or cells but also provide multifunctional signal molecules regulating bone development, regeneration, and remodeling. Endothelial cells (ECs) in bone tissues, unlike in other organ tissues, are in direct contact with the pericytes of blood vessels, resulting in a closer connection with peripheral connective tissues. Close-contact ECs contribute to osteogenesis and osteoclastogenesis by secreting various cytokines in the paracrine or juxtacrine pathways. An increasing number of studies have revealed that extracellular vesicles (EVs) derived from ECs can directly regulate maturation process of osteoblasts and osteoclasts. The different pathways focus on targets at different distances, forming the basis of the intimate spatial and temporal link between bone tissue and blood vessels. Here, we provide a systematic review to elaborate on the function of ECs in bone biology and its underlying mechanisms based on three aspects: paracrine, EVs, and juxtacrine. This review proposes the possibility of a therapeutic strategy targeting blood vessels, as an adjuvant treatment for bone disorders.

The M-CSF receptor in osteoclasts and beyond

Colony-stimulating factor 1 receptor (CSF1R, also known as c-FMS) is a receptor tyrosine kinase. Macrophage colony-stimulating factor (M-CSF) and IL-34 are ligands of CSF1R. CSF1R-mediated signaling is crucial for the survival, function, proliferation, and differentiation of myeloid lineage cells, including osteoclasts, monocytes/macrophages, microglia, Langerhans cells in the skin, and Paneth cells in the intestine. CSF1R also plays an important role in oocytes and trophoblastic cells in the female reproductive tract and in the maintenance and maturation of neural progenitor cells. Given that CSF1R is expressed in a wide range of myeloid cells, altered CSF1R signaling is implicated in inflammatory, neoplastic, and neurodegenerative diseases. Inhibiting CSF1R signaling through an inhibitory anti-CSF1R antibody or small molecule inhibitors that target the kinase activity of CSF1R has thus been a promising therapeutic strategy for those diseases. In this review, we cover the recent progress in our understanding of the various roles of CSF1R in osteoclasts and other myeloid cells, highlighting the therapeutic applications of CSF1R inhibitors in disease conditions.

Drugs directed at a key signaling receptor involved in breaking down bone tissue could help treat diseases marked by pathological bone loss and destruction. In a review article, Kyung-Hyun Park-Min and colleagues from the Hospital for Special Surgery in New York, USA, discuss the essential roles played by the colony-stimulating factor 1 receptor (CSF1R) protein in the survival, function, proliferation and differentiation of myeloid lineage stem cells in the bone marrow, including bone-resorbing osteoclasts. They explore the links between the CSF1R-mediated signaling pathway and diseases such as cancer and neurodegeneration. The authors largely focus on bone conditions, highlighting mouse studies in which CSF1R-blocking drugs were shown to ameliorate bone loss and inflammatory symptoms in models of arthritis, osteoporosis and metastatic cancer. Clinical trials are ongoing to test therapeutic applications.

Lymphatics in bone arise from pre-existing lymphatics

Bones do not normally have lymphatics. However, individuals with generalized lymphatic anomaly (GLA) or Gorham-Stout disease (GSD) develop ectopic lymphatics in bone. Despite growing interest in the development of tissue-specific lymphatics, the cellular origin of bone lymphatic endothelial cells (bLECs) is not known and the development of bone lymphatics has not been fully characterized. Here, we describe the development of bone lymphatics in mouse models of GLA and GSD. Through lineage-tracing experiments, we show that bLECs arise from pre-existing Prox1-positive LECs. We show that bone lymphatics develop in a stepwise manner where regional lymphatics grow, breach the periosteum and then invade bone. We also show that the development of bone lymphatics is impaired in mice that lack osteoclasts. Last, we show that rapamycin can suppress the growth of bone lymphatics in our models of GLA and GSD. In summary, we show that bLECs can arise from pre-existing LECs and that rapamycin can prevent the growth of bone lymphatics.

Gorham-Stout Disease of the Shoulder: Clinical, Pathologic and Therapeutic Considerations

BACKGROUND

Gorham-Stout disease (GSD) is a rare skeletal disorder characterized by massive osteolysis of a bony area in the body. When it hits the shoulder, the patient is faced with a debilitating limitation in terms of motion, stability and quality of life. GSD etiology and pathology are unknown and, as a result, therapeutic modalities remain unclear. The aim of this paper is to explore and offer medical insight into the possible etiologies, pathologies and therapeutic modalities of GSD in the shoulder.

METHODS

We explored PubMed/Medline for GSD cases in the shoulder. The search involved all articles published from database inception until February 1, 2019. Only articles published in English were included. Demographics and clinical information extrapolated from the reported cases were analyzed to deduce patterns and infer conclusions.

RESULTS

Only 32 studies met our criteria, with a total of 37 cases (n=37). Males predominated in 21 cases (57%). Twelve cases (32%) were younger than 18 years, and 18 cases (49%) were aged between 18 and 65 years. Shoulder pain was the predominant reporting symptom. The humerus was the most common shoulder site affected (54%), followed by the scapula (35%) and the clavicle (30%). Almost half of the cases affected the right shoulder (51%), the left shoulder was affected in 16 cases (43%). Conservative treatment was opted in 17 cases (46%), while surgery was performed in 13 cases (35%). Good outcomes were reported in 28 cases (76%), while death occurred twice (5%).

CONCLUSION

Understanding the demographics and clinical characteristics of GSD in the shoulder region will help in formulating better therapeutic interventions and preventive health policies.

Massive Axial and Appendicular Skeletal Deformities in Connection with Gorham-Stout Syndrome

: Background: Etiological understanding is the corner stone in the management of skeletal deformities. Methods: Multi-centre study of patients with deformities in connection with diverse etiological backgrounds. We aimed to study four patients (one boy and three girls) with variable axial and appendicular deformities in connection with a vanishing bone disorder. Results: Axial deformities such as scoliosis, kyphoscoliosis, compressed fused vertebrae, appendicular fractures, dislocations, and vicious disorganization deformities of the joints were in connection with the vanishing bone disorder, namely Gorham-Stout syndrome. Conclusions: It is mandatory to establish proper clinical and radiological phenotypic characterization in children and adults presented with unusual skeletal deformities. Identifying the reason behind these deformities is the key factor to draw a comprehensive management plan.

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.

Somatic activating mutations in PIK3CA cause generalized lymphatic anomaly

Generalized lymphatic anomaly (GLA) is a vascular disorder characterized by diffuse or multifocal lymphatic malformations (LMs). Here, Rodriguez-Laguna et al. report that somatic activating PIK3CA mutations can cause GLA, and we provide preclinical and clinical evidence to support the use of rapamycin for the treatment of GLA.

Generalized lymphatic anomaly (GLA) is a vascular disorder characterized by diffuse or multifocal lymphatic malformations (LMs). The etiology of GLA is poorly understood. We identified four distinct somatic PIK3CA variants (Glu542Lys, Gln546Lys, His1047Arg, and His1047Leu) in tissue samples from five out of nine patients with GLA. These same PIK3CA variants occur in PIK3CA-related overgrowth spectrum and cause hyperactivation of the PI3K–AKT–mTOR pathway. We found that the mTOR inhibitor, rapamycin, prevented lymphatic hyperplasia and dysfunction in mice that expressed an active form of PIK3CA (His1047Arg) in their lymphatics. We also found that rapamycin reduced pain in patients with GLA. In conclusion, we report that somatic activating PIK3CA mutations can cause GLA, and we provide preclinical and clinical evidence to support the use of rapamycin for the treatment of this disabling and deadly disease.

Successful Management of Gorham-Stout Disease in Scapula and Ribs: A Case Report and Literature Review

Gorham-Stout disease (GSD) is an extremely rare bone condition of unknown etiology characterized by spontaneous and progressive resorption of bones. GSD can occur at any age and is not related to gender, genetic inheritance, or race. Any part of the skeleton can be affected and the symptoms correlate with the sites involved. The diagnosis of GSD is established based on the combination of clinical, radiologic, and histologic features after excluding other diseases. Because of its rarity, current knowledge is limited to case reports and there is no agreement on the best strategy for treatment. The following case report describes a successfully treated case of GSD in a 26-year-old male patient with the left scapula and the 7th-9th left ribs involved. The patient was diagnosed with osteoporosis-related pleural effusion at a local hospital. In our institution, the patient was diagnosed with GSD and treated with radiotherapy and bisphosphonate. The disease was controlled and there was no evidence of disease progression during follow-up. Genetic sequencing was performed to investigate the etiology of GSD. In addition, the present study reviews the theories regarding the etiology, the clinical manifestations, the diagnostic approaches, and treatment options for this rare disease.

Modeling Rare Bone Diseases in Animals

PURPOSE OF REVIEW

The goal of this review is to highlight some of the considerations involved in creating animal models to study rare bone diseases and then to compare and contrast approaches to creating such models, focusing on the advantages and novel opportunities offered by the CRISPR-Cas system.

RECENT FINDINGS

Gene editing after creation of double-stranded breaks in chromosomal DNA is increasingly being used to modify animal genomes. Multiple tools can be used to create such breaks, with the newest ones being based on the bacterial adaptive immune system known as CRISPR/Cas. Advances in gene editing have increased the ease and speed, while reducing the cost, of creating novel animal models of disease. Gene editing has also expanded the number of animal species in which genetic modification can be performed. These changes have significantly increased the options for investigators seeking to model rare bone diseases in animals.

Combined neodymium-doped yttrium aluminum garnet laser and sclerotherapy in Gorham-Stout syndrome

Bone involvement is relatively rare in vascular malformations. Gorham-Stout disease, also referred to as vanishing bone disease, is characterized by osteoclast activation and osteolysis caused by proliferating lymphatic endothelial cells. We present the case of a 12-year-old boy who had Gorham-Stout disease at the age of 8 years. The clinical course was complicated by pathological fractures and localized intravascular consumption coagulopathy. Sclerotherapy and embolization therapy led to normalization of the coagulation parameters and significant improvement of the clinical findings. We speculate that this effect may be attributable to the elimination of lymphatic endothelial cells.

VEGF-C promotes the development of lymphatics in bone and bone loss

Patients with Gorham-Stout disease (GSD) have lymphatic vessels in their bones and their bones gradually disappear. Here, we report that mice that overexpress VEGF-C in bone exhibit a phenotype that resembles GSD. To drive VEGF-C expression in bone, we generated Osx-tTA;TetO-Vegfc double-transgenic mice. In contrast to Osx-tTA mice, Osx-tTA;TetO-Vegfc mice developed lymphatics in their bones. We found that inhibition of VEGFR3, but not VEGFR2, prevented the formation of bone lymphatics in Osx-tTA;TetO-Vegfc mice. Radiological and histological analysis revealed that bones from Osx-tTA;TetO-Vegfc mice were more porous and had more osteoclasts than bones from Osx-tTA mice. Importantly, we found that bone loss in Osx-tTA;TetO-Vegfc mice could be attenuated by an osteoclast inhibitor. We also discovered that the mutant phenotype of Osx-tTA;TetO-Vegfc mice could be reversed by inhibiting the expression of VEGF-C. Taken together, our results indicate that expression of VEGF-C in bone is sufficient to induce the pathologic hallmarks of GSD in mice.