Lentivirus transduction of human osteoclast precursor cells and differentiation into functional osteoclasts

TCIRG1 Transgenic Rescue of Osteoclast Function Using Induced Pluripotent Stem Cells Derived from Patients with Infantile Malignant Autosomal Recessive Osteopetrosis

BACKGROUND

Osteoclasts are hematopoietic stem cell-derived multinucleated cells necessary for bone remodeling and resorption. TCIRG1 encodes a protein that is an adenosine triphosphate (ATP)-dependent vacuolar proton pump required for this process. Recessive loss-of-function mutations in both copies of this gene lead to impairment of osteoclast function, with increased bone density, increased skeletal mass, and early mortality.

METHODS

We isolated fibroblasts from a patient with the compound heterozygous TCIRG1 mutations c.1549G>A (p.517D>N) and c.2236C>T (p.746Q>X), and reprogrammed them into iPS (induced pluripotent stem) cells. The function of osteoclasts derived from these cells was then rescued by transgenic expression of TCIRG1 cDNA.

RESULTS

In addition to the known effects of TCIRG1 loss of function, iPS cell-derived osteoclasts from this patient had reduced expression of the bone remodeling enzymes cathepsin K (CTSK) and tartrate-resistant acid phosphatase (TRAP), leading to reduced in vitro bone remodeling. Expression of both genes and pit formation were restored in iPS cell-derived osteoclasts following transgenic restoration of TCIRG1 expression.

CONCLUSIONS

Transgenic overexpression of TCIRG1 was sufficient to restore osteoclast function in iPS cell-derived osteoclasts from a patient with infantile malignant autosomal-recessive osteopetrosis.

CLINICAL RELEVANCE

This work provides a proof of concept for an autologous approach to treating osteopetrosis, potentially avoiding the risks associated with hematopoietic stem cell transplantation in a young patient population.

IL21R expressing CD14+CD16+ monocytes expand in multiple myeloma patients leading to increased osteoclasts

Bone marrow monocytes are primarily committed to osteoclast formation. It is, however, unknown whether potential primary alterations are specifically present in bone marrow monocytes from patients with multiple myeloma, smoldering myeloma or monoclonal gammopathy of undetermined significance. We analyzed the immunophenotypic and transcriptional profiles of bone marrow CD14⁺ monocytes in a cohort of patients with different types of monoclonal gammopathies to identify alterations involved in myeloma-enhanced osteoclastogenesis. The number of bone marrow CD14⁺CD16⁺ cells was higher in patients with active myeloma than in those with smoldering myeloma or monoclonal gammopathy of undetermined significance. Interestingly, sorted bone marrow CD14⁺CD16⁺ cells from myeloma patients were more pro-osteoclastogenic than CD14⁺CD16-cells in cultures ex vivo. Moreover, transcriptional analysis demonstrated that bone marrow CD14⁺ cells from patients with multiple myeloma (but neither monoclonal gammopathy of undetermined significance nor smoldering myeloma) significantly upregulated genes involved in osteoclast formation, including IL21R. IL21R mRNA over-expression by bone marrow CD14⁺ cells was independent of the presence of interleukin-21. Consistently, interleukin-21 production by T cells as well as levels of interleukin-21 in the bone marrow were not significantly different among monoclonal gammopathies. Thereafter, we showed that IL21R over-expression in CD14⁺ cells increased osteoclast formation. Consistently, interleukin-21 receptor signaling inhibition by Janex 1 suppressed osteoclast differentiation from bone marrow CD14⁺ cells of myeloma patients. Our results indicate that bone marrow monocytes from multiple myeloma patients show distinct features compared to those from patients with indolent monoclonal gammopathies, supporting the role of IL21R over-expression by bone marrow CD14⁺ cells in enhanced osteoclast formation.

Lentivirus transduced interleukin-1 receptor antagonist gene expression in murine bone marrow-derived mesenchymal stem cells in vitro

Genetically modified mesenchymal stem cells have been used in attempts to increase the expression of interleukin-1 receptor antagonist (IL-1Ra); however, the attempts thus far have been unsuccessful. The aim of the present study was to investigate whether the lentivirus transduced IL-1Ra gene was able to be stably expressed in murine bone marrow-derived mesenchymal stem cells (mBMSCs) in vitro. In the present study, third generation lentiviral (Lv) vectors transducing the IL-1Ra/green fluorescent protein (copGFP) gene were constructed and transfected into mBMSCs to establish the Lv.IL-1Ra.copGFP/mBMSCs, which were evaluated using fluorescence microscopy, flow cytometry, cell viability analysis using a cell counting kit-8 kit, Trypan blue staining and an MTT growth kinetics assay. The expression of IL-1Ra was analyzed using reverse transcription-quantitative polymerase chain reaction and western blotting. The results demonstrated that the Lv.IL-1Ra/copGFP vector was successfully constructed. The mBMSCs exhibited a short proliferation life, however they had good growth kinetics at an early stage and improved viability following efficient transduction of the IL-1Ra gene. IL-1Ra was overexpressed following transfection of mBMSCs. In conclusion, lentiviral vector transduced mBMSCs were able to efficiently express exogenous Il-1Ra under certain conditions and had a marked capacity for proliferation.

Lentiviral gene transfer of TCIRG1 into peripheral blood CD34(+) cells restores osteoclast function in infantile malignant osteopetrosis

Infantile malignant osteopetrosis (IMO) is a rare, lethal, autosomal recessive disorder characterized by non-functional osteoclasts. More than 50% of the patients have mutations in the TCIRG1 gene, encoding for a subunit of the osteoclast proton pump. The aim of this study was to restore the resorptive function of IMO osteoclasts by lentiviral mediated gene transfer of the TCIRG1 cDNA. CD34(+) cells from peripheral blood of five IMO patients and from normal cord blood were transduced with lentiviral vectors expressing TCIRG1 and GFP under a SFFV promoter, expanded in culture and differentiated on bone slices to mature osteoclasts. qPCR analysis and western blot revealed increased mRNA and protein levels of TCIRG1, comparable to controls. Vector corrected IMO osteoclasts generated increased release of Ca(2+) and bone degradation product CTX-I into the media as well as increased formation of resorption pits in the bone slices, while non-corrected IMO osteoclasts failed to resorb bone. Resorption was approximately 70-80% of that of osteoclasts generated from cord blood. Furthermore, transduced CD34(+) cells successfully engrafted in NSG-mice. In conclusion we provide the first evidence of lentiviral-mediated correction of a human genetic disease affecting the osteoclastic lineage.

Lentiviral small hairpin RNA knockdown of macrophage inflammatory protein-1γ ameliorates experimentally induced osteoarthritis in mice

Immune cells are involved in the pathogenesis of osteoarthritis (OA). CD4(+) T cells were activated during the onset of OA and induced macrophage inflammatory protein (MIP)-1γ expression and subsequent osteoclast formation. We evaluated the effects of local knockdown of MIP-1γ in a mouse OA model induced by anterior cruciate ligament transection. The mouse macrophage cell lines and osteoclast-like cells generated from immature hematopoietic monocyte/macrophage progenitors of murine bone marrow were cocultured with either receptor activator of NFκB ligand (RANKL) or CD4(+) T cells. The levels of MIP-1γ and RANKL in cells and mice were examined by enzyme-linked immunosorbent assay (ELISA). The osteoclastogenesis was evaluated using tartrate-resistant acid phosphatase and cathepsin K staining. OA was induced in one hind-leg knee joint of B6 mice. Lentiviral vector encoding MIP-1γ small hairpin RNA (shRNA) and control vector were individually injected intra-articularly into the knee joints, which were histologically assessed for manifestations of OA. The expression of MIP-1γ and matrix metalloproteinase (MMP)-13 and the infiltration of CD4(+) T cells, macrophages, and osteoclastogenesis in tissues were examined using immunohistochemistry. CD4(+) T cells were involved in OA by inducing MIP-1γ expression in osteoclast progenitors and the subsequent osteoclast formation. Neutralizing MIP-1γ with a specific antibody abolishes RANKL-stimulated and CD4(+) T-cell-stimulated osteoclast formation. MIP-1γ levels were significantly higher in synovium and the chondro-osseous junction of joints 90 days postsurgery. The number of infiltrated CD4(+) T cells and macrophages and IL-1β expression were reduced in the synovial tissues of mice treated with MIP-1γ shRNA. Histopathological examinations revealed that mice treated with MIP-1γ shRNA had less severe OA than control mice had, as well as decreased osteoclast formation and MMP-13 expression. Locally inhibiting MIP-1γ expression may ameliorate disease progression and provide a new OA therapy.

A specific subtype of osteoclasts secretes factors inducing nodule formation by osteoblasts

Osteoclasts are known to be important for the coupling process between bone resorption and formation. The aim of this study was to address when osteoclasts are anabolically active. Human monocytes were differentiated into mature osteoclasts by treatment with M-CSF and RANKL. Conditioned medium was collected from macrophages, pre-osteoclasts, and mature functional or non-resorbing osteopetrotic osteoclasts on either bone, plastic, decalcified bone or dentine with or without diphyllin, E64 or GM6001. Osteoclasts numbers were measured by TRACP activity. Bone resorption was evaluated by CTX-I and calcium release. The osteoblastic cell line 2T3 was treated with 50% of CM or non-CM for 12days. Bone formation was assessed by Alizarin Red extraction. CM from mature osteoclasts induced bone formation, while CM from macrophages did not. Non-resorbing osteoclasts generated from osteopetrosis patients showed little resorption, but still an induction of bone formation by osteoblasts. Mimicking the reduction in bone resorption using the V-ATPase inhibitor Diphyllin, the cysteine proteinase inhibitor E64 and the MMP-inhibitor GM6001 showed that CM from diphyllin and E64 treated osteoclasts showed reduced ability to induce bone formation compared to CM from vehicle treated osteoclasts, while CM from GM6001 treated osteoclasts equaled vehicle CM. Osteoclasts on either dentine or decalcified bone showed strongly attenuated anabolic capacities. In conclusion, we present evidence that osteoclasts, both dependent and independent of their resorptive activity, secrete factors stimulating osteoblastic bone formation.