Modulation of Dopamine Receptors on Osteoblasts as a Possible Therapeutic Strategy for Inducing Bone Formation in Arthritis.

Rheumatoid arthritis (RA) is associated with systemic osteoporosis, which leads to severe disability and low quality of life. Current therapies target osteoclasts to reduce bone degradation, but more treatment options would be required to promote bone protection by acting directly on osteoblasts (OB). Recently, the local production of dopamine in inflamed joints of RA has been observed. Thus, in this project, we aimed to determine the implication of the neurotransmitter dopamine in the bone formation process in RA. Dopamine receptors (DR) in the human bone tissue of RA or osteoarthritis (OA) patients were examined by immunohistochemistry. DR in isolated human osteoblasts (OB) was analyzed by flow cytometry, and dopamine content was evaluated by ELISA. Osteoclasts (OC) were differentiated from the PBMCs of healthy controls (HC) and RA patients. Isolated cells were treated with specific dopamine agonists. The effect of dopamine on mineralization was evaluated by Alizarin red staining. Cytokine release in supernatants was measured by ELISA. Osteoclastogenesis was evaluated with TRAP staining. OC markers were analyzed via real-time PCR and bone resorption via staining of resorption pits with toluidine blue. All DR were observed in bone tissue, especially in the bone remodeling area. Isolated OB maintained DR expression, which allowed their study in vitro. Isolated OB expressed tyrosine hydroxylase, the rate-limiting enzyme for dopamine production, and contained dopamine. The activation of D2-like DR significantly increased bone mineralization in RA osteoblasts and increased osteoclastogenesis but did not alter the expression of OC markers nor bone resorption. DR were found in the bone remodeling area of human bone tissue and dopamine can be produced by osteoblasts themselves, thus suggesting a local autocrine/paracrine pathway of dopamine in the bone. D2-like DRs are responsible for bone mineralization in osteoblasts from RA patients without an increase in bone resorption, thus suggesting the D2-like DR pathway as a possible future therapeutic target to counteract bone resorption in arthritis.

Dopamine induces in vitro migration of synovial fibroblast from patients with rheumatoid arthritis.

Preventing synovial fibroblast (SF) migration into the adjacent cartilage is a desirable therapeutic target in rheumatoid arthritis (RA). As previous studies demonstrated that RASF and SF from osteoarthritis (OA) patients express dopamine receptors (DR), aim of the present study was to investigate the impact of dopamine on mobility of fibroblasts from patients with chronic arthritides. Synovial tissue and fibroblasts were obtained from RA and OA patients. Immunohistochemistry was performed for all DR-subtypes in the invasion zone. Migration- and motility-assays were performed under DR-stimulation. Cytokines were evaluated using ELISA. Expression of DRs was evaluated by flow cytometry, and DR activation was measured by xCELLigence real-time analysis. All DRs were expressed in RA invasion zone. Migration and motility of RASF and OASF were increased after DR stimulation in patients ≤ 75 years old. Synovial fibroblasts from older RA patients (> 75 years old) expressed lower levels of D1-, D2- and D4-DR than patients ≤ 75 years old. DR activation was not altered in older patients. Our results suggest a possible involvement of dopamine on migration of fibroblasts from arthritis patients. Therefore, the synovial dopaminergic pathway might represent a potential therapeutic target to interfere with progressive joint damage in RA patients.

Mesenchymal Stem Cells Form 3D Clusters Following Intraventricular Transplantation.

Mesenchymal stem cells (MSCs) are regarded as an immune privileged cell type with numerous regeneration-promoting effects. The in vivo behavior of MSC and underlying mechanisms leading to their regenerative effects are largely unknown. The aims of this study were to comparatively investigate the in vivo behavior of canine (cMSC), human (hMSC), and murine MSC (mMSC) following intra-cerebroventricular transplantation. At 7 days post transplantation (dpt), clusters of cMSC, hMSC, and mMSC were detected within the ventricular system. At 49 dpt, cMSC-transplanted mice showed clusters mostly consisting of extracellular matrix lacking transplanted MSC. Similarly, hMSC-transplanted mice lacked MSC clusters at 49 dpt. Xenogeneic MSC transplantation was associated with a local T lymphocyte-dominated immune reaction at both time points. Interestingly, no associated inflammation was observed following syngeneic mMSC transplantation. In conclusion, transplanted MSC formed intraventricular cell clusters and exhibited a short life span in vivo. Xenogeneically in contrast to syngeneically transplanted MSC triggered a T cell-mediated graft rejection indicating that MSCs are not as immune privileged as previously assumed. However, MSC may mediate their effects by a "hit and run" mechanism and future studies will show whether syngeneically or xenogeneically transplanted MSCs exert better therapeutic effects in animals with CNS disease.

The antiviral drug ganciclovir does not inhibit microglial proliferation and activation.

Ganciclovir is effective in the treatment of human infections with viruses of the Herpesviridae family. Beside antiviral properties, recently ganciclovir was described to inhibit microglial proliferation and disease severity of experimental autoimmune encephalomyelitis, an inflammatory model of multiple sclerosis. Microglial activation and proliferation are main characteristics of neuroinflammatory CNS diseases and inhibition of microglial functions might be beneficial in autoimmune diseases, or detrimental in infectious diseases. The objective of this study was to determine potential inhibitory effects of ganciclovir in three different murine animal models of CNS neuroinflammation in which microglia play an important role: Theiler´s murine encephalomyelitis, the cuprizone model of de- and remyelination, and the vesicular stomatitis virus encephalitis model. In addition, in vitro experiments with microglial cultures were performed to test the hypothesis that ganciclovir inhibits microglial proliferation. In all three animal models, neither microglial proliferation or recruitment nor disease activity was changed by ganciclovir. In vitro experiments confirmed that microglial proliferation was not affected by ganciclovir. In conclusion, our results show that the antiviral drug ganciclovir does not inhibit microglial activation and proliferation in the murine CNS.

Mesenchymal stem cells do not exert direct beneficial effects on CNS remyelination in the absence of the peripheral immune system.

Remyelination is the natural repair mechanism in demyelinating disorders such as multiple sclerosis (MS) and it was proposed that it might protect from axonal loss. For unknown reasons, remyelination is often incomplete or fails in MS lesions and therapeutic treatments to enhance remyelination are not available. Recently, the transplantation of exogenous mesenchymal stem cells (MSC) has emerged as a promising tool to enhance repair processes. This included the animal model experimental autoimmune encephalomyelitis (EAE), a commonly used model for the autoimmune mechanisms of MS. However, in EAE it is not clear if the beneficial effect of MSC derives from a direct influence on brain resident cells or if this is an indirect phenomenon via modulation of the peripheral immune system. The aim of this study was to determine potential regenerative functions of MSC in the toxic cuprizone model of demyelination that allows studying direct effects on de- and remyelination without the influence of the peripheral immune system. MSC from three different species (human, murine, canine) were transplanted either intraventricularly into the cerebrospinal fluid or directly into the lesion of the corpus callosum at two time points: at the onset of oligodendrocyte progenitor cell (OPC) proliferation or the peak of OPC proliferation during cuprizone induced demyelination. Our results show that MSC did not exert any regenerative effects after cuprizone induced demyelination and oligodendrocyte loss. During remyelination, MSC did not influence the dynamics of OPC proliferation and myelin formation. In conclusion, MSC did not exert direct regenerative functions in a mouse model where peripheral immune cells and especially T lymphocytes do not play a role. We thus suggest that the peripheral immune system is required for MSC to exert their effects and this is independent from a direct influence of the central nervous system.

Oligodendroglial markers in the cuprizone model of CNS de- and remyelination.

Oligodendrocytes are the myelinating cells of the central nervous system. Since many studies of demyelinating diseases focus their research on this cell type, there is growing interest for obtaining reliable markers that can specifically recognize oligodendroglia. Established markers are the myelin-associated neurite outgrowth inhibitor (NogoA), the transcription factor Olig2, and the antibody CC-1, the latter being directed against the protein adenomatous polyposis coli (APC). Unfortunately, it has been discussed whether APC and Olig2 could recognize astrocytes under pathological conditions as well. Hence, we performed immunohistochemical studies using the oligodendroglial markers NogoA, APC, and Olig2 in a murine model of cuprizone induced demyelination. We have found that APC co-localizes with NogoA and does not co-localize with the astrocytic marker GFAP. Olig2 shows co-localization with APC but there is also a small population of Olig2/GFAP double positive cells. Some Olig2/GFAP double positive cells are found in the corpus callosum in a narrow time window in which oligodendrocyte precursor cells proliferate in this model. In other brain regions including the cerebral cortex and hippocampus and in all regions in untreated control mice double positive Olig2/GFAP cells do not occur. In conclusion, our results underline that APC and NogoA are reliable markers for detection of mature oligodendrocytes. Olig2 is a suitable marker to stain cells of oligodendroglial origin but could be combined with GFAP to exclude the GFAP positive population of cells from the quantification of oligodendroglia.

Pivotal role of choline metabolites in remyelination.

Neuroprotective approaches for central nervous system regeneration have not been successful in clinical practice so far and compounds that enhance remyelination are still not available for patients with multiple sclerosis. The objective of this study was to determine potential regenerative effects of the substance cytidine-5'-diphospho (CDP)-choline in two different murine animal models of multiple sclerosis. The effects of exogenously applied CDP-choline were tested in murine myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis. In addition, the cuprizone-induced mouse model of de- and remyelination was used to specifically test the hypothesis that CDP-choline directly increases remyelination. We found that CDP-choline ameliorated the disease course of experimental autoimmune encephalomyelitis and exerted beneficial effects on myelin, oligodendrocytes and axons. After cuprizone-induced demyelination, CDP-choline effectively enhanced myelin regeneration and reversed motor coordination deficits. The increased remyelination arose from an increase in the numbers of proliferating oligodendrocyte precursor cells and oligodendrocytes. Further in vitro studies suggest that this process is regulated by protein kinase C. We thus identified a new mechanism to enhance central nervous system remyelination via the choline pathway. Due to its regenerative action combined with an excellent safety profile, CDP-choline could become a promising substance for patients with multiple sclerosis as an add-on therapy.

Modified extracorporeal photopheresis with cells from a healthy donor for acute graft-versus-host disease in a mouse model.

BACKGROUND: Graft-versus-host disease (GvHD) is a major challenge after hematopoietic stem cell transplantation but treatment options for patients are still limited. In many cases first-line treatment with glucocorticoids is not successful. Among second-line therapies the extracorporeal photopheresis (ECP) is frequently performed, due to induction of selective tolerance instead of general immunosuppression. However, for some patients with severe acute GvHD the leukapheresis step of the ECP procedure is physically exhausting and limits the number of ECP cycles. METHODS: We hypothesized that leukocytes from healthy cell donors could be used as a replacement for ECP leukocytes gained from the GvHD patient. For this purpose we used a well established mouse model of acute GvHD. The ECP therapy was based on cells with the genetic background of the initial donor of the stem cell transplantation. As a precondition we developed a protocol representing conventional ECP in mice equivalent to clinical used ECP setup. RESULTS: We could demonstrate that conventional, clinically derived ECP setup is able to alleviate acute GvHD. By using leukocytes obtained from healthy mice with the bone marrow donor's genetic background we could not observe a statistically significant therapeutic effect. CONCLUSIONS: Conventional human ECP setup is effective in the mouse model of severe acute GvHD. In addition we could not prove that ECP cells from healthy mice with bone marrow donor's genetic background are as effective as ECP cells derived from GvHD mice. Based on our findings, new questions arise for further studies, in which the cellular characteristics for ECP mediated immune tolerance are a matter of investigation.

Effects of murine and human bone marrow-derived mesenchymal stem cells on cuprizone induced demyelination.

For the treatment of patients with multiple sclerosis there are no regenerative approaches to enhance remyelination. Mesenchymal stem cells (MSC) have been proposed to exert such regenerative functions. Intravenous administration of human MSC reduced the clinical severity of experimental autoimmune encephalomyelitis (EAE), an animal model mimicking some aspects of multiple sclerosis. However, it is not clear if this effect was achieved by systemic immunomodulation or if there is an active neuroregeneration in the central nervous system (CNS). In order to investigate remyelination and regeneration in the CNS we analysed the effects of intravenously and intranasally applied murine and human bone marrow-derived MSC on cuprizone induced demyelination, a toxic animal model which allows analysis of remyelination without the influence of the peripheral immune system. In contrast to EAE no effects of MSC on de- and remyelination and glial cell reactions were found. In addition, neither murine nor human MSC entered the lesions in the CNS in this toxic model. In conclusion, MSC are not directed into CNS lesions in the cuprizone model where the blood-brain-barrier is intact and thus cannot provide support for regenerative processes.