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Background Hereditary multiple exostoses (HME) is a rare skeletal disorder characterised by a widespread. distribution of osteochondromas originating from the metaphyses of long bones. Case presentation This case study examines a 55-year-old male cadaver bequeathed to the University of Liverpool who suffered from HME, thus providing an exceptionally rare opportunity to examine the anatomical changes associated with this condition. Conclusions Findings from imaging and dissection indicated that this was a severe case of HME in terms of the quantity and distribution of the osteochondromas and the number of synostoses present. In addition, the existence of enchondromas and the appearance of gaps within the trabeculae of affected bones make this a remarkable case. This study provides a comprehensive overview of the morbidity of the disease as well as adding to the growing evidence that diseases concerning benign cartilaginous tumours may be part of a spectrum rather than distinct entities.

Metachondromatosis is a rare disorder of autosomal inheritance with incomplete penetrance, which is characterized by formation of osteochondroma and enchondroma, caused by loss of function of the protein tyrosine phosphatase nonreceptor type 11 (PTPN11) gene. Diagnosis is made based on the distribution and orientation of lesions with history of regression of lesions with time and confirmed by genetic mutation of PTPN11 gene. We report a rare case of a 24-year-old male with Alport's syndrome with metachondromatosis due to missense variation in PTPN11 gene.

The maturation and function of osteoblasts (OBs) rely heavily on the reversible phosphorylation of signaling proteins. To date, most of the work in OBs has focused on phosphorylation by tyrosyl kinases, but little has been revealed about dephosphorylation by protein tyrosine phosphatases (PTPases). SHP2 (encoded by PTPN11) is a ubiquitously expressed PTPase. PTPN11 mutations are associated with both bone and cartilage manifestations in patients with Noonan syndrome (NS) and metachondromatosis (MC), although the underlying mechanisms remain elusive. Here, we report that SHP2 deletion in bone gamma-carboxyglutamate protein-expressing (Bglap+) bone cells leads to massive osteopenia in both trabecular and cortical bones due to the failure of bone cell maturation and enhanced osteoclast activity, and its deletion in Bglap+ chondrocytes results in the onset of enchondroma and osteochondroma in aged mice with increased tubular bone length. Mechanistically, SHP2 was found to be required for osteoblastic differentiation by promoting RUNX2/OSTERIX signaling and for the suppression of osteoclastogenesis by inhibiting STAT3-mediated RANKL production by osteoblasts and osteocytes. These findings are likely to explain the compromised skeletal system in NS and MC patients and to inform the development of novel therapeutics to combat skeletal disorders.

Rationale: Metachondromatosis (MC) is a very rare genetic disease, which is infrequently reported worldwide, which leads to osteochondroma and enchondromatosis. The disease has been shown to be associated with loss of function of the tumor suppressor gene “protein tyrosine phosphatase, non-receptor type 11” (PTPN11). Patient concerns: A 12-year-old female was admitted to the hospital with pain due to an enlarged mass in her left fifth finger. Diagnosis: Examination of the left hand by computed tomography (CT) revealed an expanding type of round and low-density lesion in the fifth proximal phalanx. The patient then underwent technetium-99m methylene diphosphonate single-photon emission CT/CT (99mTc-MDP SPECT/CT) to assess the nature of the lesion. The SPECT/CT image revealed dilated osteopathy and increased activity of the fifth proximal phalanx on the left hand. Unexpectedly, the examination of the right hand revealed slight expanded lesions and increased activities of the third metacarpal and proximal phalange, as well as the fourth proximal phalange and the middle phalanx. On the basis of the patient's symptoms and the results of the above-mentioned examinations, we diagnosed the patient as having MC in her hands. Intervention: Considering the pain of the fifth finger of the left hand, the patient underwent debridement of the fifth proximal phalanx of the left hand and internal fixation with bone graft taken from the body. Outcomes: The patient was discharged after a week of observation. One year later, she was admitted to the hospital again for removal of the bone healing internal fixation after osteoma surgery. Preoperative 99mTc-MDP SPECT/CT revealed that the left-handed lesions displayed postoperative changes, while the multiple lesions in the right hand increased in volume but remained unchanged in number. Lessons: This case revealed the CT and 99mTc-MDP SPECT/CT imaging features of MC. Specifically, SPECT/CT imaging contributed to the diagnosis of clinically asymptomatic bone lesions, and the 3D SPECT/CT fusion allowed a more comprehensive and intuitive view of the lesion by combining anatomy and function.

Chondrocytes in the epiphyseal cartilage undergo terminal differentiation prior to their removal through apoptosis. To examine the role of ERK1 and ERK2 in chondrocyte terminal differentiation, we generated Osterix (Osx)-Cre; ERK1–/–; ERK2flox/flox mice (conditional knockout Osx [cKOosx]), in which ERK1 and ERK2 were deleted in hypertrophic chondrocytes. These cKOosx mice were grossly normal in size at birth, but by 3 weeks of age exhibited shorter long bones. Histological analysis in these mice revealed that the zone of hypertrophic chondrocytes in the growth plate was markedly expanded. In situ hybridization and quantitative real-time PCR analyses demonstrated that Matrix metalloproteinase-13 (Mmp13) and Osteopontin expression was significantly decreased, indicating impaired chondrocyte terminal differentiation. Moreover, Egr1 and Egr2, transcription factors whose expression is restricted to the last layers of hypertrophic chondrocytes in wild-type mice, were also strongly downregulated in these cKOosx mice. In transient transfection experiments in the RCS rat chondrosarcoma cell line, the expression of Egr1, Egr2, or a constitutively active mutant of MEK1 increased the activity of an Osteopontin promoter, whereas the MEK1-induced activation of the Osteopontin promoter was inhibited by the coexpression of Nab2, an Egr1 and Egr2 co-repressor. These results suggest that MEK1-ERK signaling activates the Osteopontin promoter in part through Egr1 and Egr2. Finally, our histological analysis of cKOosx mice demonstrated enchondroma-like lesions in the bone marrow that are reminiscent of human metachondromatosis, a skeletal disorder caused by mutations in PTPN11. Our observations suggest that the development of enchondromas in metachondromatosis may be caused by reduced extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK MAPK) signaling. © 2014 American Society for Bone and Mineral Research.

Transdifferentiation of hypertrophic chondrocytes into bone-forming osteoblasts has been reported, yet the underlying molecular mechanism remains incompletely understood. SHP2 is an ubiquitously expressed cytoplasmic protein tyrosine phosphatase. SHP2 loss-of-function mutations in chondroid cells are linked to metachondromatosis in humans and mice, suggesting a crucial role for SHP2 in the skeleton. However, the specific role of SHP2 in skeletal cells has not been elucidated. To approach this question, we ablated SHP2 in collagen 2α1(Col2α1)-Cre- and collagen 10α1(Col10α1)-Cre-expressing cells, predominantly proliferating and hypertrophic chondrocytes, using “Cre-loxP”-mediated gene excision. Mice lacking SHP2 in Col2α1-Cre-expressing cells die at mid-gestation. Postnatal SHP2 ablation in the same cell population caused dwarfism, chondrodysplasia and exostoses. In contrast, mice in which SHP2 was ablated in the Col10α1-Cre-expressing cells appeared normal but were osteopenic. Further mechanistic studies revealed that SHP2 exerted its influence partly by regulating the abundance of SOX9 in chondrocytes. Elevated and sustained SOX9 in SHP2-deficient hypertrophic chondrocytes impaired their differentiation to osteoblasts and impaired endochondral ossification. Our study uncovered an important role of SHP2 in bone development and cartilage homeostasis by influencing the osteogenic differentiation of hypertrophic chondrocytes and provided insight into the pathogenesis and potential treatment of skeletal diseases, such as osteopenia and osteoporosis.

Metachondromatosis is a benign bone disease predominantly observed in the hands and feet of children or young adults demonstrating two different manifestations: a cartilage-capped bony outgrowth on the surface of the bone called exostosis and ectopic cartilaginous nodules inside the bone called enchondroma. Recently, it has been reported that loss-of-function mutations of the SHP2 gene, which encodes the SHP2 protein tyrosine phosphatase, are associated with metachondromatosis. The purpose of this study was to investigate the role of SHP2 in postnatal cartilage development, which is largely unknown. We disrupted Shp2 during the postnatal stage of mouse development in a chondrocyte-specific manner using a tamoxifen-inducible system. We found tumor-like nodules on the hands and feet within a month after the initial induction. The SHP2-deficient mice demonstrated an exostosis-like and enchondroma-like phenotype in multiple bones of the hands, feet, and ribs as assessed by X-ray and micro-computed tomography (CT). Histological assessment revealed the disorganization of the growth plate cartilage, a cartilaginous protrusion from the epiphyseal bone, and ectopic cartilage nodules within the bones, which is consistent with the pathological features of metachondromatosis in humans (ie, both exostosis and enchondroma). At molecular levels, we observed an abundant expression of Indian hedgehog protein (IHH) and fibroblast growth factor 2 (FGF2) and impaired expression of mitogen-activated protein kinases (MAPK) in the affected cartilage nodules in the SHP2-deficient mice. In summary, we have generated a mouse model of metachondromatosis that includes manifestations of exostosis and enchondroma. This study provides a novel model for the investigation of the pathophysiology of the disease and advances the understanding of metachondromatosis. This model will be useful to identify molecular mechanisms for the disease cause and progression as well as to develop new therapeutic strategies in the future.

The tyrosine phosphatase SHP2, encoded by PTPN11, is required for the survival, proliferation and differentiation of various cell types. Germline activating mutations in PTPN11 cause Noonan syndrome, whereas somatic PTPN11 mutations cause childhood myeloproliferative disease and contribute to some solid tumours. Recently, heterozygous inactivating mutations in PTPN11 were found in metachondromatosis, a rare inherited disorder featuring multiple exostoses, enchondromas, joint destruction and bony deformities. The detailed pathogenesis of this disorder has remained unclear. Here we use a conditional knockout (floxed) Ptpn11 allele (Ptpn11(fl)) and Cre recombinase transgenic mice to delete Ptpn11 specifically in monocytes, macrophages and osteoclasts (lysozyme M-Cre; LysMCre) or in cathepsin K (Ctsk)-expressing cells, previously thought to be osteoclasts. LysMCre;Ptpn11(fl/fl) mice had mild osteopetrosis. Notably, however, CtskCre;Ptpn11(fl/fl) mice developed features very similar to metachondromatosis. Lineage tracing revealed a novel population of CtskCre-expressing cells in the perichondrial groove of Ranvier that display markers and functional properties consistent with mesenchymal progenitors. Chondroid neoplasms arise from these cells and show decreased extracellular signal-regulated kinase (ERK) pathway activation, increased Indian hedgehog (Ihh) and parathyroid hormone-related protein (Pthrp, also known as Pthlh) expression and excessive proliferation. Shp2-deficient chondroprogenitors had decreased fibroblast growth factor-evoked ERK activation and enhanced Ihh and Pthrp expression, whereas fibroblast growth factor receptor (FGFR) or mitogen-activated protein kinase kinase (MEK) inhibitor treatment of chondroid cells increased Ihh and Pthrp expression. Importantly, smoothened inhibitor treatment ameliorated metachondromatosis features in CtskCre;Ptpn11(fl/fl) mice. Thus, in contrast to its pro-oncogenic role in haematopoietic and epithelial cells, Ptpn11 is a tumour suppressor in cartilage, acting through a FGFR/MEK/ERK-dependent pathway in a novel progenitor cell population to prevent excessive Ihh production.

Rationale Metachondromatosis (MC) is a very rare genetic disease, which is infrequently reported worldwide, which leads to osteochondroma and enchondromatosis. The disease has been shown to be associated with loss of function of the tumor suppressor gene "protein tyrosine phosphatase, non-receptor type 11" (PTPN11). Patient concerns A 12-year-old female was admitted to the hospital with pain due to an enlarged mass in her left fifth finger. Diagnosis Examination of the left hand by computed tomography (CT) revealed an expanding type of round and low-density lesion in the fifth proximal phalanx. The patient then underwent technetium-99m methylene diphosphonate single-photon emission CT/CT (Tc-MDP SPECT/CT) to assess the nature of the lesion. The SPECT/CT image revealed dilated osteopathy and increased activity of the fifth proximal phalanx on the left hand. Unexpectedly, the examination of the right hand revealed slight expanded lesions and increased activities of the third metacarpal and proximal phalange, as well as the fourth proximal phalange and the middle phalanx. On the basis of the patient's symptoms and the results of the above-mentioned examinations, we diagnosed the patient as having MC in her hands. Intervention Considering the pain of the fifth finger of the left hand, the patient underwent debridement of the fifth proximal phalanx of the left hand and internal fixation with bone graft taken from the body. Outcomes The patient was discharged after a week of observation. One year later, she was admitted to the hospital again for removal of the bone healing internal fixation after osteoma surgery. Preoperative Tc-MDP SPECT/CT revealed that the left-handed lesions displayed postoperative changes, while the multiple lesions in the right hand increased in volume but remained unchanged in number. Lessons This case revealed the CT and Tc-MDP SPECT/CT imaging features of MC. Specifically, SPECT/CT imaging contributed to the diagnosis of clinically asymptomatic bone lesions, and the 3D SPECT/CT fusion allowed a more comprehensive and intuitive view of the lesion by combining anatomy and function.

Activation of the signalling molecule SHP2 is implicated in driving several cancers. In a newly described class of bone-progenitor cells, however, it seems that the protein acts as a tumour suppressor. See Letter p.491 Inactivation of PTPN11, which encodes the phosphatase SHP2, is the cause of the inherited cartilage tumour disorder metachondromatosis. Using a mouse model, Wentian Yang and colleagues show that deletion of the Ptpn11 gene in osteoclasts leads to metachondromatosis that originates in a newly identified mesenchymal progenitor population in the perichondrial groove of Ranvier. Ptpn11 loss acts by activating hedgehog signalling, and metachondromatosis can be ameliorated in this model by hedgehog pathway inhibitors. Therefore in contrast to other tumour types where it promotes tumour formation, Ptpn11 suppresses tumorigenesis in cartilage tissue.

Background: Metachondromatosis is a condition that causes gross conical metaphyseal expansion (sometimes irregular), cortical thinning, exostoses. Metachondromatous lesions occur mainly in the extremities and are roughly symmetrical. The lesions can involve the bones of the hand and all long bones in the arms and legs. The distribution in this case additionally involved the acromion process and ischia. The bone changes, although dramatic, can be confused with other types of metaphyseal dysplasia such as Gaucher disease and multiple exostoses. Objective: This paper will review the literature with regard to Metachondromatosis, Gaucher disease and Osteochondromatosis due to their similarities. The case study serves as an example of these findings and documents a history of fractures secondary to the obvious bone changes. Discussion: Clinical manifestations of these conditions and how they may present to the manual therapist are discussed. With respect to Metachondromatosis, the manual therapist needs to be mindful of pathological fractures that can occur with little trauma. Manual therapists are cautioned against using long bones as levers for spinal manipulation in these patients.

Recently, loss-of-function mutations in PTPN11 were linked to the cartilage tumor syndrome metachondromatosis (MC), a rare inherited disorder featuring osteochondromas, endochondromas and skeletal deformation. However, the underlying molecular and cellular mechanism for MC remained incompletely understood. By studying the role of the Src homology-2 domain-containing protein tyrosine phosphatase Shp2 (encoded by mouse Ptpn11) in cathepsin K-expressing cells, we identified a novel cell population in the perichondrial groove of Ranvier. In the absence of Shp2, these cells exhibit elevated Indian hedgehog (Ihh) signaling, proliferate excessively and cause ectopic cartilage formation and tumors. Our findings establish a critical role for a protein-tyrosine phosphatase (PTP) family member, in addition to the well-known roles of receptor tyrosine kinases (RTKs), in cartilage development and homeostasis. However, whether Shp2 deficiency in other epiphyseal chondroid cells and whether signaling pathways in addition to the IHH/Parathyroid Hormone-related Peptide (PTHrP) axis attribute to the formation of enchondromas and osteochondromas remains elusive. Understanding how chondrogenic events are regulated by SHP2 could aid in the development of novel therapeutic approaches to prevent and treat cartilage diseases, such as MC and osteoarthritis (OA).

Introduction Metachondromatosis is a rare genetic disease of osteochondroma and enchondroma formation, caused by loss of function of the PTPN11 gene. It is distinct from other similar conditions such as multiple osteochondromas and hereditary multiple exostoses by the distribution and orientation of lesions, and pattern of inheritance. Lesions typically occur in hands, feet, femora, tibiae and the pelvis. Lesions are typically reported to regress in adulthood. Methods We reviewed the current literature on metachondromatosis, and present four new cases in a family with metachondromatosis. Results Long-term follow up data reveal spontaneous regression of lesions by skeletal maturity. Complications may include nerve palsy due to the mass effect of lesions, avascular necrosis of the femoral head and angular deformity of long bones. Histopathological analysis has demonstrated that lesions in metachondromatosis are a mix of osteochondromas and enchondromas; however, one case of chondrosarcoma has been reported. Conclusion Lesions associated with metachondromatosis may cause a variety of complications due to mass effects; however, they are often asymptomatic, cause cosmetic concerns and, importantly, most regress spontaneously. Regular clinical review with selective imaging to monitor for such complications is appropriate, but uncomplicated lesions are unlikely to require surgical intervention.

Metachondromatosis (MC) is a rare, autosomal dominant, incompletely penetrant combined exostosis and enchondromatosis tumor syndrome. MC is clinically distinct from other multiple exostosis or multiple enchondromatosis syndromes and is unlinked to EXT1 and EXT2, the genes responsible for autosomal dominant multiple osteochondromas (MO). To identify a gene for MC, we performed linkage analysis with high-density SNP arrays in a single family, used a targeted array to capture exons and promoter sequences from the linked interval in 16 participants from 11 MC families, and sequenced the captured DNA using high-throughput parallel sequencing technologies. DNA capture and parallel sequencing identified heterozygous putative loss-of-function mutations in PTPN11 in 4 of the 11 families. Sanger sequence analysis of PTPN11 coding regions in a total of 17 MC families identified mutations in 10 of them (5 frameshift, 2 nonsense, and 3 splice-site mutations). Copy number analysis of sequencing reads from a second targeted capture that included the entire PTPN11 gene identified an additional family with a 15 kb deletion spanning exon 7 of PTPN11. Microdissected MC lesions from two patients with PTPN11 mutations demonstrated loss-of-heterozygosity for the wild-type allele. We next sequenced PTPN11 in DNA samples from 54 patients with the multiple enchondromatosis disorders Ollier disease or Maffucci syndrome, but found no coding sequence PTPN11 mutations. We conclude that heterozygous loss-of-function mutations in PTPN11 are a frequent cause of MC, that lesions in patients with MC appear to arise following a “second hit,” that MC may be locus heterogeneous since 1 familial and 5 sporadically occurring cases lacked obvious disease-causing PTPN11 mutations, and that PTPN11 mutations are not a common cause of Ollier disease or Maffucci syndrome., Author Summary Children with cartilage tumor syndromes form multiple tumors of cartilage next to joints. These tumors can occur inside the bones, as with Ollier disease and Maffuci syndrome, or on the surface of bones, as in the Multiple Osteochondroma syndrome (MO). In a hybrid syndrome, called metachondromatosis (MC), patients develop tumors both on and within bones. Only the genes causing MO are known. Since MC is inherited, we studied genetic markers in an affected family and found a region of the genome, encompassing 100 genes, always passed on to affected members. Using a recently developed method, we captured and sequenced all 100 genes in multiple families and found mutations in one gene, PTPN11, in 11 of 17 families. Patients with MC have one mutant copy of PTPN11 from their affected parent and one normal copy from their unaffected parent in all cells. We found that the normal copy is additionally lost in cartilage cells that form tumors, giving rise to cells without PTPN11. Mutations in PTPN11 were not found in other cartilage tumor syndromes, including Ollier disease and Maffucci syndrome. We are currently working to understand how loss of PTPN11 in cartilage cells causes tumors to form.

Background Enchondromatosis represent a heterogenous group of disorders. Spranger et al attempted a classification into 6 types: Ollier disease, Maffuci syndrome, metachondromatosis, spondyloenchondrodysplasia, enchondromatosis with irregular vertebral lesions, and generalized enchondromatosis. Halal and Azouz added 3 tentative categories to the 6 in the classification of Spranger et al. Case presentation We report on a 15-year-old boy with acrofrom upper limbs and mixed appearance of radiolucency, cysts and striae of fibro-chondromatosis. Lower limbs (femoral, tibial and fibular dysplasia showed enlarged metaphyses near the knees bilaterally) were present. Additional features of short stature, macrocephaly, facial dysmorphism, and generalised platyspondyly have been encountered. These bone shortenings were associated with bone bending, curving and rhizomelia of the upper limbs with significant macrodactyly. Limitations in articular movements were present. The forearm deformities were similar to those observed in hereditary multiple exostosis. Conclusion The acrofrom upper limbs with mixed appearances of radiolucencies, cysts and striae of fibro-chondromatosis are the basic features of type I1Spranger. The constellation of facial dysmorphic features and significant vertebral abnormalities in our present patient were not compatible with the above-mentioned type of enchondromatosis. Our report widens the knowledge of disorders characterised by enchondromatosis. Ascertainment of the mode of inheritance in our present patient was difficult because of insufficient family history and parents declined clinical/radiographic documentation.

Dysplasia epiphysealis hemimelica (DEH) and metachondromatosis (MC) are considered in the differential diagnosis of solitary and hereditary osteochondromas. Both are rare disorders with DEH demonstrating cartilaginous overgrowth of an epiphysis and MC exhibiting synchronous enchondromas and osteochondromas. Ten cases of DEH and two of MC were compared with osteochondromas at the histological and molecular level. Histologically, clumping of chondrocytes within a fibrillary chondroid matrix is characteristic of DEH, while osteochondromas and MC display the characteristic growth plate architecture. Using cDNA microarray analysis we demonstrate that DEH and MC cluster separately from osteochondromas and growth plates. The EXT genes, involved in the hereditary multiple osteochondromas syndrome, and downregulated in osteochondroma, were normally expressed in DEH and MC as shown by quantitative reverse transcriptase-polymerase chain reaction (qPCR). EXT is involved in heparan sulphate biosynthesis, important for Indian Hedgehog/ParaThyroid Hormone Like Hormone (IHH/PTHLH) growth plate signalling pathways. IHH/PTHLH signalling molecules were expressed in DEH and MC as shown by both qPCR and immunohistochemistry, suggesting that this pathway is active. This is in contrast to osteochondroma, in which PTHLH signalling is downregulated. Thus, lesions of DEH and MC are separate entities from osteochondroma as confirmed by their different cDNA and protein expression profiles. Downstream targets of EXT, which are downregulated in osteochondroma, are expressed in DEH and MC, suggesting that EXT signalling is not disturbed.

Loss of PTPN11/SHP2 in mice or in human metachondromatosis (MC) patients causes benign cartilage tumors on the bone surface (exostoses) and within bones (enchondromas). To elucidate the mechanisms underlying cartilage tumor formation, we investigated the role of SHP2 in the specification, maturation and organization of chondrocytes. Firstly, we studied chondrocyte maturation by performing RNA-seq on primary chondrocyte pellet cultures. We found that SHP2 depletion, or inhibition of the ERK1/2 pathway, delays the terminal differentiation of chondrocytes from the early-hypertrophic to the late-hypertrophic stage. Secondly, we studied chondrocyte maturation and organization in mice with a mosaic postnatal inactivation of Ptpn11 in chondrocytes. We found that the vertebral growth plates of these mice have expanded domains of early-hypertrophic chondrocytes that have not yet terminally differentiated, and their enchondroma-like lesions arise from chondrocytes displaced from the growth plate due to a disruption in the organization of maturation and ossification zones. Furthermore, we observed that lesions from human MC patients also display disorganized chondrocyte maturation zones. Next, we found that inactivation of Ptpn11 in Fsp1-Cre-expressing fibroblasts induces exostosis-like outgrowths, suggesting that loss of SHP2 in cells on the bone surface and at bone-ligament attachment sites induces ectopic chondrogenesis. Finally, we performed lineage tracing to show that exostoses and enchondromas in mice likely contain mixtures of wild-type and SHP2-deficient chondrocytes. Together, these data indicate that in patients with MC, who are heterozygous for inherited PTPN11 loss-of-function mutations, second-hit mutations in PTPN11 can induce enchondromas by disrupting the organization and delaying the terminal differentiation of growth plate chondrocytes, and can induce exostoses by causing ectopic chondrogenesis of cells on the bone surface. Furthermore, the data are consistent with paracrine signaling from SHP2-deficient cells causing SHP2-sufficient cells to be incorporated into the lesions., Author Summary Patients with the inherited disorder, metachondromatosis (MC), develop multiple benign cartilage tumors during childhood. MC patients carry heterozygous loss-of-function mutations in the PTPN11 gene, and their cartilage tumors likely arise when the second PTPN11 allele is lost due to a somatic mutation. PTPN11 encodes a phosphatase called SHP2 that is involved in a variety of signaling pathways. Here, we use mouse models and cell culture assays to investigate the mechanisms by which loss of SHP2 promotes cartilage tumor formation. We show that cartilage tumors that form inside bones (enchondromas) likely arise due to disorganized growth and delayed terminal differentiation of growth plate chondrocytes, while cartilage tumors that form on the bone surface (exostoses) can arise due to ectopic chondrogenesis of fibroblast-like cells that surround bones. We also suggest that paracrine signals from SHP2-deficient cells cause neighboring SHP2-sufficient cells to contribute to exostoses and enchondromas. Finally, we provide in vitro data that the ERK1/2 pathway is regulated by SHP2 and promotes chondrocyte terminal differentiation. Together, our data provide insight into the mechanisms underlying cartilage tumor formation and implicate SHP2 as a key regulator of chondrocyte specification, organization and maturation.

Corrigendum: Ptpn11 deletion in a novel progenitor causes metachondromatosis by inducing hedgehog signalling

Cartilage tumors, accounting for 22% of skeletal system tumors, are characterized by the formation of exostoses, enchondroma(s) or both, and cause significant morbidity and mortality. Both benign and malignant cartilaginous tumors can develop at various ages, and can show autosomal dominant inheritance or occur sporadically. The molecular mechanism underlying the development and progression of these cartilaginous lesions remains incompletely understood. Shp2, encoded by the Ptpn11 gene, is one of two Src homology 2 domain-containing protein-tyrosine phosphatases, and is required for most, if not all, receptor tyrosine kinase (RTK), cytokine, and integrin signaling pathways. Global deletion of Shp2 in mice results in early embryonic lethality, whereas postnatal Shp2 deficiency in various tissues/cells has diverse effects on their development and function. Several human malignancies, most notably childhood myeloproliferative disorders, are associated with Ptpn11 gain-of-function (GOF) mutations. Several lines of evidence indicate that Shp2 plays an important role in skeletal development and homoeostasis; however, little is known about its role in vivo. Recently Ptpn11 truncated mutations (presumably protein null) are reported to cause human metachondromatosis, a benign cartilage tumor syndrome with malignant potentials. By taking a tissue-specific gene knockout approach, we report here that Shp2 loss-of-function mutation, in contrast to its GOF mutants in other tissues/cells, causes widespread and severe cartilaginous tumors, strongly suggesting that Shp2 has a tissue specific-tumor suppressor function. These studies also identify the target of cartilage malignancies caused by Shp2 deficiency as a novel cell population with stem/progenitor properties located within the groove of Ranvier. Materials and Methods: Mice carrying Ptpn11 floxed (fl) or cathepsin K-Cre (Ctsk-Cre) were described previously. To generate Ctsk-expressing cell specific Shp2 deficient mice and study the role of Shp2 in these cells to regulate skeletal development and homeostasis, Ptpn11 floxed mice were bred to Ctsk-Cre mice to generate Ptpn11fl/fl;Ctsk-Cre (KO) and Ptpn11fl/+;Ctsk-Cre (Control) animals. To track the fate of Ctsk+ cartilaginous cells in vivo in the presence or absence of Shp2, Roza26lacZ (R26lacZ) and Roza26EYFP (R26YFP) reporter alleles were bred to Control and KO mice to generate Control/R26YFP, KO/R26YFP, Control/R26lacZ and KO/R26lacZ compound mice, respectively. YFP-positive cartilaginous cells were isolated by serial enzymatic digestions of epiphyseal cartilage with hyaluronidase/Trypsin/ collagenase D and FACS sorting. Cell surface marker expression was determined by FACS analysis after staining with fluorescence-labeled antibodies. For histological analysis, skeletal tissues were removed from mice after euthanasia and fixed in 4% paraformaldehyde; after decalcification, embedding, and sectioning, they were stained with H&E, alcian blue, and Safranin-O to visualize general histological structure and ECM expression or stained with specific antibodies indicated to visualize the activation or expression of certain signal molecules. Microcomputed Tomography (µ-CT) and x-ray analysis were conducted to visualize the microstructure and bone mineral density (BMD). Results and Discussion: KO mice, compared to Controls, were born at the expected Mendelian ratio and appeared normal at birth. However, Ctsk expressing cell-specific Shp2 deficient KO mice rapidly developed a complex skeletal disease manifested as scoliosis, formation of exostoses and enchondroma, and increased BMD. The mobility of KO mice, compared to that of Controls, was rapidly diminished due to multiple joint deformations. As expected, the number of tartrate resistant acid phosphatase positive (TRAP+) multinuclear osteoclasts substantially decreased in KO mice in vivo and in vitro. These observations are further supported by our q-PCR data that the expression of M-CSF- and RANKL-evoked osteoclastogenic genes (MMP9, Calcitonin receptor, TRAP and c-Fos) were all compromised by Shp2 deficiency. However, detailed studies, including bone marrow transplantation experiments and comparisons with Ptpn11fl/fl;LysMCre mcie, revealed that the cartilage phenotype in KO mice was not osteoclast-autonomous. Therefore to identify the cellular origin of the cartilage lesions in KO mice, we conducted a reporter study by using Ctsk-Cre mediated R26lacZ or YFP expression. Surprisingly, we found that the Ctsk promoter is active not only in mature osteoclasts, but also in a subset of cells that live in perichondrial groove of Ranvier. Deficiency of Shp2 in these cells causes unrestrained proliferation, chondrogenic differentiation, and exostoses/enchondroma(s) formation. These cells were found to share several mesenchymal/chondroprogenitor markers, such as CD44, CD90, Stro1 and jagged1. Biochemical analysis shows that Shp2 deficiency impaired Erk activation and caused elevated expression of Indian hedgehog (Ihh) and PTHrP in cartilage lesions. In summary, we specifically ablated Shp2 in Ctsk-expressing cells (primarily in mature osteoclasts and subsets of cartilaginous cells) in mice and found that Shp2, in addition to having a role in osteoclastogenesis in vitro and in vivo, negatively regulates the proliferation and chondrogenic differentiation of a unique population of ctsk+ perichondrial cartilaginous cells. Loss of Shp2 in these cells causes cell proliferation, chondrogenic differentiation, and cartilage tumorigenesis at the metaphyses of tubular bones. This phenotype is strikingly similar to the human disease metachondromatosis. Mechanistically, we believe that this pathogenic process is triggered by ectopic and/or elevated Ihh expression due to impaired Erk activation in Shp2- deficient perichondrial cells. If confirmed, these data identify hedgehog pathway inhibitors as potential therapeutic agents in metachromatosis patients. Our results, in concert with previous studies, show that, depending on the cellular context, Shp2 can act as an oncogene or a tumor suppressor gene. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr SY15-01. doi:1538-7445.AM2012-SY15-01

Multiple osteochondromas (MO) is characterised by development of two or more cartilage capped bony outgrowths (osteochondromas) of the long bones. The prevalence is estimated at 1:50,000, and it seems to be higher in males (male-to-female ratio 1.5:1). Osteochondromas develop and increase in size in the first decade of life, ceasing to grow when the growth plates close at puberty. They are pedunculated or sessile (broad base) and can vary widely in size. The number of osteochondromas may vary significantly within and between families, the mean number of locations is 15–18. The majority are asymptomatic and located in bones that develop from cartilage, especially the long bones of the extremities, predominantly around the knee. The facial bones are not affected. Osteochondromas may cause pain, functional problems and deformities, especially of the forearm, that may be reason for surgical removal. The most important complication is malignant transformation of osteochondroma towards secondary peripheral chondrosarcoma, which is estimated to occur in 0.5–5%. MO is an autosomal dominant disorder and is genetically heterogeneous. In almost 90% of MO patients germline mutations in the tumour suppressor genes EXT1 or EXT2 are found. The EXT genes encode glycosyltransferases, catalyzing heparan sulphate polymerization. The diagnosis is based on radiological and clinical documentation, supplemented with, if available, histological evaluation of osteochondromas. If the exact mutation is known antenatal diagnosis is technically possible. MO should be distinguished from metachondromatosis, dysplasia epiphysealis hemimelica and Ollier disease. Osteochondromas are benign lesions and do not affect life expectancy. Management includes removal of osteochondromas when they give complaints. Removed osteochondromas should be examined for malignant transformation towards secondary peripheral chondrosarcoma. Patients should be well instructed and regular follow-up for early detection of malignancy seems justified. For secondary peripheral chondrosarcoma, en-bloc resection of the lesion and its pseudocapsule with tumour-free margins, preferably in a bone tumour referral centre, should be performed.