Dynamic expression of VDR and 1-­alpha-­hydroxylase in differentiated and re-­differentiated human articular chondrocytes

Abstract of a presentation at a conference of the International Cartilage Repair Society.Purpose: The goal was to investigate potential roles played by vitamin D in the regulation of joint cartilage biology. We studied the expression of two central elements of vitamin D metabolism, namely the vitamin D receptor and its converting enzyme 1­α­hydroxylase in human knee cartilage and chondrocytes. Methods and Materials: Expression of receptor and enzyme was determined by immunohistochemistry/immunofluorescence, reversetranscriptase PCR and western blot on differentiated, de­differentiated and re­differentiated chondrocytes. Cartilage was harvested from a macroscopically healthy looking area of the lateral femoral condyle during knee replacement surgery in 4 otherwise healthy patients aged 50­70. Suspension cultures of differentiated chondrocytes were established by short enzymatic digestion of cartilage using Collagenase XI and further incubation in non­adherent vessels. De­differentiated cells were the result of serial expansion of chondrocytes during 4 weeks after isolation in monolayers cultures. Chondrocyte re­differentiation was achieved by propagating cell pellets for 3 weeks in the presence of chondro­inductive morphogens. Results: Both protein and gene expression of vitamin D receptor appear to be very low or undetectable in native cartilage and/or differentiated chondrocytes. In contrast, receptor expression was upregulated in dedifferentiated cells after monolayer expansion, however, this upregulation was lost when cells regained chondrogenic phenotype in 3D pellets. The expression of 1­α­hydroxylase was observed on the superficial layer of chondrocytes in native cartilage, which correlated with weak but detectable outcomes by PCR and western blot on differentiated cultures. Similarly, levels of the enzyme were increased after cell expansion in monolayers and decreased in 3D pellet cultures. Conclusion: Our study uncover a previously unknown regulation of vitamin D receptor between differentiated and redifferentiated phenotypes in cartilage cells. Furthermore, this study is pioneering on investigating the expression of 1­α­hydroxylase in cartilage tissue and chondrocytes. Further work is needed to ascertain if receptor and enzyme expression is regulated in disease conditions or affected by inflammatory environments

Immunobiology of cancer-associated fibroblasts in the context of radiotherapy

Radiotherapy (RT) still represents a mainstay of treatment in clinical oncology. Traditionally, the effectiveness of radiotherapy has been attributed to the killing potential of ionizing radiation (IR) over malignant cells, however, it has become clear that therapeutic efficacy of RT also involves activation of innate and adaptive anti-tumor immune responses. Therapeutic irradiation of the tumor microenvironment (TME) provokes profound cellular and biological reconfigurations which ultimately may influence immune recognition. As one of the major constituents of the TME, cancer-associated fibroblasts (CAFs) play central roles in cancer development at all stages and are recognized contributors of tumor immune evasion. While some studies argue that RT affects CAFs negatively through growth arrest and impaired motility, others claim that exposure of fibroblasts to RT promotes their conversion into a more activated phenotype. Nevertheless, despite the well-described immunoregulatory functions assigned to CAFs, little is known about the interplay between CAFs and immune cells in the context of RT. In this review, we go over current literature on the effects of radiation on CAFs and the influence that CAFs have on radiotherapy outcomes, and we summarize present knowledge on the transformed cellular crosstalk between CAFs and immune cells after radiation

Expression and function of Leukotriene B4 receptors in human articular chondrocytes

Leukotriene B4 (LTB4) is linked to osteoarthritis (OA) development however the expression of LTB4 receptors in cartilage cells and the physiological effects of LTB4 on cartilage tissue remain unknown. In this study we find that human articular chondrocytes express LTB4 receptors and that these receptors are functional, however, LTB4 does not seem to affect importantly some primary chondrocyte functions

Radiotherapy and the tumor stroma: the importance of dose and fractionation

Ionizing radiation (IR) is a non-specific but highly effective way to kill malignant cells. However, tumor recurrence sustained by a minor fraction of surviving tumor cells is a commonplace phenomenon caused by the activation of both cancer cell intrinsic resistance mechanisms, and also extrinsic intermediaries of therapy resistance, represented by non-malignant cells and structural components of the tumor stroma. The improved accuracy offered by advanced radiotherapy (RT)-technology permits reduced volume of healthy tissue in the irradiated field, and has been triggering an increase in the prescription of high-dose oligo-fractionated regimens in the clinics. Given the remarkable clinical success of high-dose RT and the current therapeutic shift occurring in the field, in this review we revise the existing knowledge on the effects that different radiation regimens exert on the different compartments of the tumor microenvironment, and highlight the importance of anti-tumor immunity and other tumor cell extrinsic mechanisms influencing therapeutic responses to high-dose radiation

Radiation-Induced Transformation of Immunoregulatory Networks in the Tumor Stroma

The implementation of novel cancer immunotherapies in the form of immune checkpoint blockers represents a major advancement in the treatment of cancer, and has renewed enthusiasm for identifying new ways to induce antitumor immune responses in patients. Despite the proven efficacy of neutralizing antibodies that target immune checkpoints in some refractory cancers, many patients do not experience therapeutic benefit, possibly owing to a lack of antitumor immune recognition, or to the presence of dominant immunosuppressive mechanisms in the tumor microenvironment (TME). Recent developments in this field have revealed that local radiotherapy (RT) can transform tumors into in situ vaccines, and may help to overcome some of the barriers to tumor-specific immune rejection. RT has the potential to ignite tumor immune recognition by generating immunogenic signals and releasing neoantigens, but the multiple immunosuppressive forces in the TME continue to represent important barriers to successful tumor rejection. In this article, we review the radiation-induced changes in the stromal compartments of tumors that could have an impact on tumor immune attack. Since different RT regimens are known to mediate strikingly different effects on the multifarious elements of the tumor stroma, special emphasis is given to different RT schedules, and the time after treatment at which the effects are measured. A better understanding of TME remodeling following specific RT regimens and the window of opportunity offered by RT will enable optimization of the design of novel treatment combinations

Dynamic expression of VDR and 1-­alpha-­hydroxylase in differentiated and re-­differentiated human articular chondrocytes

Purpose: The goal was to investigate potential roles played by vitamin D in the regulation of joint cartilage biology. We studied the expression of two central elements of vitamin D metabolism, namely the vitamin D receptor and its converting enzyme 1­α­hydroxylase in human knee cartilage and chondrocytes. Methods and Materials: Expression of receptor and enzyme was determined by immunohistochemistry/immunofluorescence, reversetranscriptase PCR and western blot on differentiated, de­differentiated and re­differentiated chondrocytes. Cartilage was harvested from a macroscopically healthy looking area of the lateral femoral condyle during knee replacement surgery in 4 otherwise healthy patients aged 50­70. Suspension cultures of differentiated chondrocytes were established by short enzymatic digestion of cartilage using Collagenase XI and further incubation in non­adherent vessels. De­differentiated cells were the result of serial expansion of chondrocytes during 4 weeks after isolation in monolayers cultures. Chondrocyte re­differentiation was achieved by propagating cell pellets for 3 weeks in the presence of chondro­inductive morphogens. Results: Both protein and gene expression of vitamin D receptor appear to be very low or undetectable in native cartilage and/or differentiated chondrocytes. In contrast, receptor expression was upregulated in dedifferentiated cells after monolayer expansion, however, this upregulation was lost when cells regained chondrogenic phenotype in 3D pellets. The expression of 1­α­hydroxylase was observed on the superficial layer of chondrocytes in native cartilage, which correlated with weak but detectable outcomes by PCR and western blot on differentiated cultures. Similarly, levels of the enzyme were increased after cell expansion in monolayers and decreased in 3D pellet cultures. Conclusion: Our study uncover a previously unknown regulation of vitamin D receptor between differentiated and redifferentiated phenotypes in cartilage cells. Furthermore, this study is pioneering on investigating the expression of 1­α­hydroxylase in cartilage tissue and chondrocytes. Further work is needed to ascertain if receptor and enzyme expression is regulated in disease conditions or affected by inflammatory environments

Co-expression of 1α-hydroxylase and vitamin D receptor in human articular chondrocytes

Background: The aim was to investigate whether resident chondrocytes in human articular cartilage and in subculture express vitamin D receptor (VDR) and the enzyme that hydroxylates the prohormone 25(OH)D3 to the active hormone 1α,25(OH)2D3, namely 1α-hydroxylase (CYP27B1). Any putative effects of vitamin D on chondrocytes were also explored. Methods: Cartilage from human osteoarthritic knee joints, cultured chondrocytes and cells grown in 3D spheroids were examined for the expression of VDR and 1α-hydroxylase by PCR, Western blots and immunolabelling. Receptor engagement was judged by visualizing nuclear translocation. The effects of 25(OH)D3 and 1α,25(OH)2D3 on chondrocyte functions were assessed in proliferation-, chondrogenesis- and cartilage signature-gene expression assays. The capability of chondrocytes to hydroxylate 25(OH)D3 was determined by measuring the concentration of metabolites. Finally, a putative regulation of receptor and enzyme expression by 1α,25(OH)2D3 or interleukin (IL)-1β, was investigated by Western blot. Results: Gene expression was positive for VDR in freshly isolated cells from native cartilage, cells subcultured in monolayers and in spheroids, whereas protein expression, otherwise judged low, was apparent in monolayers. Nuclear translocation of VDR occurred upon 1α,25(OH)2D3 treatment. Transcripts for 1α-hydroxylase were detected in freshly isolated cells, cultured cells and spheroids. Western blots and immunolabelling detected 1α-hydroxylase protein in all materials, while staining of tissue appeared confined to cells at the superficial layer. A dose-dependent 1α,25(OH)2D3 production was measured when the enzyme substrate was supplied to cell cultures. Western blots revealed that the VDR, but not 1α-hydroxylase, was induced by IL-1β treatment in adherent cells. Proliferation in monolayers was enhanced by both 25(OH)D3 and 1α,25(OH) 2D3, and both compounds had negative effects on chondrogenesis and cartilage-matrix genes. Conclusions: VDR expression in resident cartilage chondrocytes, generally considered differentiated cells, is elusive. A similar pattern applies for redifferentiated chondrocytes in spheroid cultures, whereas dedifferentiated cells, established in monolayers, stably express VDR. Both 25(OH)D3 and 1α,25(OH)2D3 are able to potentiate cell proliferation but have a negative impact in proteoglycan synthesis. Chondrocytes express 1α-hydroxylase and may contribute to the production of 1α,25(OH)2D3 into the joint environment. Effects of vitamin D could be unfavourable in the context of cartilage matrix synthesis

Mesenchymal stromal cells from human umbilical cords display poor chondrogenic potential in scaffold-free three dimensional cultures

Many researchers world over are currently investigating the suitability of stromal cells harvested from foetal tissues for allogeneic cell transplantation therapies or for tissue engineering purposes. In this study, we have investigated the chondrogenic potential of mesenchymal stromal cells (MSCs) isolated from whole sections of human umbilical cord or mixed cord (UCSCs-MC), and compared them with cells isolated from synovial membrane (SMSCs), Hoffa’s fat pad (HFPSCs) and cartilage. All MSCs were positive for surface markers including CD73, CD90, CD105, CD44, CD146 and CD166, but negative for CD11b, CD19, CD34, CD45 and HLA-DR in addition to CD106 and CD271. Chondrogenic potential of all cell sources was studied using 3D pellet cultures incubated in the presence of different combinations of anabolic substances such as dexamethasone, IGF-1, TGF-β1, TGF-β3, BMP-2 and BMP-7. BMP-2 and dexamethasone in combination with TGF-β1 or TGF-β3 excelled at inducing chondrogenesis on SMSCs, HFPSCs and chondrocytes, as measured by glycosaminoglycans and collagen type II staining of pellets, quantitative glycosaminoglycan expression, quantitative PCR of cartilage signature genes and electron microscopy. In contrast, none of the tested growth factor combinations was sufficient to induce chondrogenesis on UCSCs-MC. Moreover, incubation of UCSCs-MC spheroids in the presence of cartilage pieces or synovial cells in co-cultures did not aid chondrogenic induction. In summary, we show that in comparison with MSCs harvested from adult joint tissues, UCSCs-MC display poor chondrogenic abilities. This observation should alert researchers at the time of considering UCSCs-MC as cartilage forming cells in tissue engineering or repair strategies

Large-scale secretome analyses unveil the superior immunosuppresive phenotype of umbilical cord stromal cells as compared to other adult mesenchymal stromal cells

Mesenchymal stromal cells (MSCs), given their regenerative potential, are being investigated as a potential therapeutic tool for cartilage lesions. MSCs express several bioactive molecules which act in a paracrine fashion to modulate the tissue microenvironment. Yet, little is known about the divergence of these signalling molecules in different MSC populations. The present study investigated secretomes of stromal cells harvested from Hoffa’s fat pad (HFPSCs), synovial membrane (SMSCs), umbilical cord (UCSCs) and cartilage (ACs) by quantitative liquid chromatography-mass spectrometry (LC-MS/MS) proteomics. Also, multiplex protein arrays and functional assays were performed to compare the constitutive immunomodulatory capabilities of different MSCs. Proteins involved in extracellular matrix degradation and inflammation, such as matrix metalloproteinases (MMPs), interleukin (IL)-17 and complement factors, were downregulated in UCSCs as compared to adult cell sources. Additionally, secretion of transforming growth factor (TGF)-β1 and prostaglandin E2 (PGE2) was enhanced in UCSC supernatants. UCSCs were superior in inhibiting peripheral blood mononuclear cell (PBMC) proliferation, migration and cytokine secretion as compared to adult stromal cells. SMSCs significantly suppressed the proliferation of PBMCs only if they were primed with pro-inflammatory cytokines. Although all cell types repressed human leukocyte antigen-DR isotype (HLADR) surface expression and cytokine release by activated macrophages, only UCSCs significantly blocked IL-6 and IL-12 production. Furthermore, UCSCs supernatants increased aggrecan gene expression in twodimensional chondrocyte cultures. The data demonstrated that UCSCs displayed superior anti-inflammatory and immunosuppressive properties than stromal cells from adult tissues. This allogeneic cell source could potentially be considered as an adjuvant therapy for articular cartilage repair

Ionizing radiation curtails immunosuppressive effects from cancer-associated fibroblasts on dendritic cells

Cancer-associated fibroblasts (CAFs) participate actively in tumor development and affect treatment responses, by among other mechanisms, promoting an immunosuppressive tumor microenvironment. In contrast to normal fibroblasts, reactive CAFs secrete a myriad of immunomodulatory soluble factors at high levels, i.e. growth factors, cytokines, and chemokines, which directly influence tumor immunity and inflammation. CAFs have been identified as important players in tumor radioresistance. However, knowledge on the immunomodulatory functions of CAFs during/after radiotherapy is still lacking. In this study, we investigated the effects of ionizing radiation on CAF-mediated regulation of dendritic cells (DCs). CAFs were obtained from freshly operated lung cancer tissues, while DCs were procured from peripheral blood of healthy donors. Experimental settings comprised both co-cultures and incubations with conditioned medium from control and irradiated CAFs. Functional assays to study DC differentiation/activation consisted on cytokine release, expression of cell-surface markers, antigen uptake, migration rates, T cell priming, and DC-signaling analysis. We demonstrate that CAFs induce a tolerogenic phenotype in DCs by promoting down-regulation of: i) signature DC markers (CD14, CD1a, CD209); ii) activation markers (CD80, CD86, CD40, and HLA-DR) and iii) functional properties (migration, antigen uptake, and CD4+ T cell priming). Notably, some of these effects were lost in conditioned medium from CAFs irradiated at fractionated medium-dose regimens (3x6 Gy). However, the expression of relevant CAF-derived regulatory agents like thymic stromal lymphopoietin (TSLP) or tryptophan 2,3-dioxygenase (TDO2) was unchanged upon irradiation. This study demonstrates that CAFs interfere with DC immune functions and unveil that certain radiation regimens may reverse CAF-mediated immunosuppressive effects