Dermal white adipose tissue derived IL-33 regulates interleukin 4/13 expression in myeloid cells during inflammation.

Effective tissue response to infection and injury essentially relies on the fine-tuned induction and subsequent resolution of inflammation. Recent research highlighted multiple functions of dermal white adipose tissue (dWAT) beyond its traditional role as an energy reservoir. However, in contrast to other fat depots, there are only limited data about putative immune-regulatory functions of dWAT. Therefore, we investigated the impact of dWAT in the control of an acute skin inflammation. Skin inflammation triggers the activation of dWAT. In turn, soluble mediators of activated dWAT stimulate the expression of numerous genes controlling skin inflammation including the Th2 cell cytokines interleukin-4 (IL-4) and interleukin-13 (IL-13) in myeloid cells in vitro. Consistently, myeloid cells isolated from inflamed skin showed a significant upregulation of IL-4/13 expression compared to those isolated from healthy skin. Mechanistically, we demonstrate that interleukin-33 (IL-33) released from activated dWAT is responsible for IL-4/13 stimulation in myeloid cells. Interestingly, obesity attenuates IL-33 secretion in dWAT during inflammation resulting in decreased IL-4 and IL-13 expression in myeloid cells. Our data reveal an IL-33 - IL-4/13 signaling cascade initiated from dWAT in a Th2 independent context of inflammation that may contribute to limitation of inflammation. This cascade seems to be disturbed in obese individuals with prolonged inflammation.

Thy-1 restricts steatosis and liver fibrosis in steatotic liver disease.

BACKGROUND AND AIMS: Steatotic liver disease (SLD) is generally considered to represent a hepatic manifestation of metabolic syndrome and includes a disease spectrum comprising isolated steatosis, metabolic dysfunction-associated steatohepatitis, liver fibrosis and ultimately cirrhosis. A better understanding of the detailed underlying pathogenic mechanisms of this transition is crucial for the design of new and efficient therapeutic interventions. Thymocyte differentiation antigen (Thy-1, also known as CD90) expression on fibroblasts controls central functions relevant to fibrogenesis, including proliferation, apoptosis, cytokine responsiveness, and myofibroblast differentiation. METHODS: The impact of Thy-1 on the development of SLD and progression to fibrosis was investigated in high-fat diet (HFD)-induced SLD wild-type and Thy-1-deficient mice. In addition, the serum soluble Thy-1 (sThy-1) concentration was analysed in patients with metabolic dysfunction-associated SLD stratified according to steatosis, inflammation, or liver fibrosis using noninvasive markers. RESULTS: We demonstrated that Thy-1 attenuates the development of fatty liver and the expression of profibrogenic genes in the livers of HFD-induced SLD mice. Mechanistically, Thy-1 directly inhibits the profibrotic activation of nonparenchymal liver cells. In addition, Thy-1 prevents palmitic acid-mediated amplification of the inflammatory response of myeloid cells, which might indirectly contribute to the pronounced development of liver fibrosis in Thy-1-deficient mice. Serum analysis of patients with metabolically associated steatotic liver disease syndrome revealed that sThy-1 expression is correlated with liver fibrosis status, as assessed by liver stiffness, the Fib4 score, and the NAFLD fibrosis score. CONCLUSION: Our data strongly suggest that Thy-1 may function as a fibrosis-protective factor in mouse and human SLD.

Atypical fibroxanthoma and pleomorphic dermal sarcoma - gene expression analysis compared with undifferentiated cutaneous squamous cell carcinoma.

BACKGROUND: The histogenetic origin of atypical fibroxanthoma (AFX) and pleomorphic dermal sarcoma (PDS) has not been definitively elucidated. In addition to a fibroblastic origin, a keratinocytic differentiation is discussed due to strong clinical, histomorphological and molecular genetic similarities with undifferentiated cutaneous squamous cell carcinoma (cSCC). PATIENTS AND METHODS: 56 cases (36 AFXs, 8 PDSs, 12 undifferentiated cSCCs) were evaluated for their clinical, histomorphological, and immunohistochemical characteristics. RNA transcriptome analysis was performed on 18 cases (6 AFXs/PDSs, 6 undifferentiated cSCCs, 6 differentiated cSCCs). RESULTS: Clinically, the strong similarities in age, gender and tumor location were confirmed. Without further immunohistochemical staining, histomorphological differentiation between AFX/PDS and undifferentiated cSCC is often impossible. Principal component analysis of the RNA transcriptome analysis showed that AFX/PDS and differentiated cSCC each formed their own cluster, while the undifferentiated cSCCs fall in between these two groups, but without forming a cluster of their own. When examining differentially expressed genes (DEGs), the heat maps showed that there were cases within the undifferentiated cSCC that were more likely to be AFX/PDS than differentiated cSCC based on their expression profile. CONCLUSIONS: The results provide evidence of molecular similarities between AFX/PDS and undifferentiated cSCC and suggest a common histogenetic origin.

Antifibrotic Soluble Thy-1 Correlates with Renal Dysfunction in Chronic Kidney Disease.

Kidney fibrosis is a major culprit in the development and progression of chronic kidney disease (CKD), ultimately leading to the irreversible loss of organ function. Thymocyte differentiation antigen-1 (Thy-1) controls many core functions of fibroblasts relevant to fibrogenesis but is also found in a soluble form (sThy-1) in serum and urine. We investigated the association of sThy-1 with clinical parameters in patients with CKD receiving hemodialysis treatment compared to individuals with a preserved renal function. Furthermore, Thy-1 tissue expression was detected in a mouse model of diabetic CKD (eNOS-/-; db/db) and non-diabetic control mice (eNOS-/-). Serum and urinary sThy-1 concentrations significantly increased with deteriorating renal function, independent of the presence of diabetes. Serum creatinine is the major, independent, and inverse predictor of serum sThy-1 levels. Moreover, sThy-1 is not only predicted by markers of renal function but is also itself an independent and strong predictor of markers of renal function, i.e., serum creatinine. Mice with severe diabetic CKD show increased Thy-1 mRNA and protein expression in the kidney compared to control animals, as well as elevated urinary sThy-1 levels. Pro-fibrotic mediators, such as interleukin (IL)-4, IL-13, IL-6 and transforming growth factor ß, increase Thy-1 gene expression and release of sThy-1 from fibroblasts. Our data underline the role of Thy-1 in the control of kidney fibrosis in CKD and raise the opportunity that Thy-1 may function as a renal antifibrotic factor.

IL17F Expression as an Early Sign of Oxidative Stress-Induced Cytotoxicity/Apoptosis.

Interleukin 17F (IL17F) has been found to be involved in various inflammatory pathologies and has recently become a target for therapeutic purposes. In contrast to IL17F secreted by immune cells, the focus of this study is to describe the triggers of IL17F release in non-immune cells with a particular focus on IL17F-induced fibrosis. IL17F induction was examined in human lung epithelial (BEAS-2B) and myeloid cell lines as well as in peripheral blood mononuclear cells after in vitro exposure to aqueous cigarette smoke extract (CSE), inorganic mercury, cadmium or the apoptosis inducer brefeldin A. Fibrosis was examined in vitro, evaluating the transition of human primary dermal fibroblasts to myofibroblasts. We observed that all stressors were able to induce IL17F gene expression regardless of cell type. Interestingly, its induction was associated with cytotoxic/apoptotic signs. Inhibiting oxidative stress by N-acetylcysteine abrogated CSE-induced cytotoxic and IL17F-inducing effects. The induction of IL17F was accompanied by IL17F protein expression. The transition of fibroblasts into myofibroblasts was not influenced by either recombinant IL17F or supernatants of CSE-exposed BEAS-2B. In addition to IL17F secretion by specialized or activated immune cells, we underscored the cell type-independent induction of IL17F by mechanisms of inhibitable oxidative stress-induced cytotoxicity. However, IL17F was not involved in dermal fibrosis under the conditions used in this study.

Sulfated hyaluronic acid inhibits the hyaluronidase CEMIP and regulates the HA metabolism, proliferation and differentiation of fibroblasts.

Hyaluronan (HA) is an extracellular matrix component that regulates a variety of physiological and pathological processes. The function of HA depends both on its overall amount and on its size, properties that are controlled by HA synthesizing and degrading enzymes. The lack of inhibitors that can specifically block individual HA degrading enzymes has hampered attempts to understand the contribution of individual hyaluronidases to different physiological and pathological processes. CEMIP is a recently discovered hyaluronidase that cleaves HA through mechanisms and under conditions that are distinct from those of other hyaluronidases such as HYAL1 or HYAL2. The role of its hyaluronidase activity in physiology and disease is poorly understood. Here, we characterized a series of sulfated HA derivatives (sHA) with different sizes and degrees of sulfation for their ability to inhibit specific hyaluronidases. We found that highly sulfated sHA derivatives potently inhibited CEMIP hyaluronidase activity. One of these compounds, designated here as sHA3.7, was characterized further and shown to inhibit CEMIP with considerable selectivity over other hyaluronidases. Inhibition of CEMIP with sHA3.7 in fibroblasts, which are the main producers of HA in the interstitial matrix, increased the cellular levels of total and high molecular weight HA, while decreasing the fraction of low molecular weight HA fragments. Genetic deletion of CEMIP in mouse embryonic fibroblasts (MEFs) produced analogous results and confirmed that the effects of sHA3.7 on HA levels were mediated by CEMIP inhibition. Importantly, both CEMIP deletion and its inhibition by sHA3.7 suppressed fibroblast proliferation, while promoting differentiation into myofibroblasts, as reflected in a lack of CEMIP in myofibroblasts within skin wounds in experimental mice. By contrast, adipogenic and osteogenic differentiation were attenuated upon CEMIP loss or inhibition. Our results demonstrate the importance of CEMIP for the HA metabolism, proliferation and differentiation of fibroblasts, and suggest that inhibition of CEMIP with sulfated HA derivatives such as sHA3.7 has potential utility in pathological conditions that are dependent on CEMIP function.

Danger signal extracellular calcium initiates differentiation of monocytes into SPP1/osteopontin-producing macrophages.

The danger signal extracellular calcium is pathophysiologically increased in the synovial fluid of patients with rheumatoid arthritis (RA). Calcium activates the NLRP3-inflammasome via the calcium-sensing receptor in monocytes/macrophages primed by lipopolysaccharide, and this effect is mediated by the uptake of calciprotein particles (CPPs) formed out of calcium, phosphate, and fetuin-A. Aim of the study was to unravel the influence of calcium on monocytes when the priming signal is not present. Monocytes were isolated from the blood of healthy controls and RA patients. Macrophages were characterized using scRNA-seq, DNA microarray, and proteomics. Imaging flow cytometry was utilized to study intracellular events. Here we show that extracellular calcium and CPPs lead to the differentiation of monocytes into calcium-macrophages when the priming signal is absent. Additional growth factors are not needed, and differentiation is triggered by calcium-dependent CPP-uptake, lysosomal alkalization due to CPP overload, and TFEB- and STAT3-dependent increased transcription of the lysosomal gene network. Calcium-macrophages have a needle-like shape, are characterized by excessive, constitutive SPP1/osteopontin production and a strong pro-inflammatory cytokine response. Calcium-macrophages differentiated out of RA monocytes show a stronger manifestation of this phenotype, suggesting the differentiation process might lead to the pro-inflammatory macrophage response seen in the RA synovial membrane.

Protease-Triggered Release of Stabilized CXCL12 from Coated Scaffolds in an Ex Vivo Wound Model.

Biomaterials are designed to improve impaired healing of injured tissue. To accomplish better cell integration, we suggest to coat biomaterial surfaces with bio-functional proteins. Here, a mussel-derived surface-binding peptide is used and coupled to CXCL12 (stromal cell-derived factor 1α), a chemokine that activates CXCR4 and consequently recruits tissue-specific stem and progenitor cells. CXCL12 variants with either non-releasable or protease-mediated-release properties were designed and compared. Whereas CXCL12 was stabilized at the N-terminus for protease resistance, a C-terminal linker was designed that allowed for specific cleavage-mediated release by matrix metalloproteinase 9 and 2, since both enzymes are frequently found in wound fluid. These surface adhesive CXCL12 derivatives were produced by expressed protein ligation. Functionality of the modified chemokines was assessed by inositol phosphate accumulation and cell migration assays. Increased migration of keratinocytes and primary mesenchymal stem cells was demonstrated. Immobilization and release were studied for bioresorbable PCL-co-LC scaffolds, and accelerated wound closure was demonstrated in an ex vivo wound healing assay on porcine skin grafts. After 24 h, a significantly improved CXCL12-specific growth stimulation of the epithelial tips was already observed. The presented data display a successful application of protein-coated biomaterials for skin regeneration.

Collagen/glycosaminoglycan-based matrices for controlling skin cell responses.

Wound healing and tissue regeneration are orchestrated by the cellular microenvironment, e.g. the extracellular matrix (ECM). Including ECM components in biomaterials is a promising approach for improving regenerative processes, e.g. wound healing in skin. This review addresses recent findings for enhanced epidermal-dermal regenerative processes on collagen (coll)/glycosaminoglycan (GAG)-based matrices containing sulfated GAG (sGAG) in simple and complex in vitro models. These matrices comprise 2D-coatings, electrospun nanofibrous scaffolds, and photo-crosslinked acrylated hyaluronan (HA-AC)/coll-based hydrogels. They demonstrated to regulate keratinocyte and fibroblast migration and growth, to stimulate melanogenesis in melanocytes from the outer root sheath (ORS) of hair follicles and to enhance the epithelial differentiation of human mesenchymal stem cells (hMSC). The matrices' suitability for delivery of relevant growth factors, like heparin-binding epidermal growth factor like growth factor (HB-EGF), further highlights their potential as bioinspired, functional microenvironments for enhancing skin regeneration.

Matrix Remodeling and Hyaluronan Production by Myofibroblasts and Cancer-Associated Fibroblasts in 3D Collagen Matrices.

The tumor microenvironment is a key modulator in cancer progression and has become a novel target in cancer therapy. An increase in hyaluronan (HA) accumulation and metabolism can be found in advancing tumor progression and are often associated with aggressive malignancy, drug resistance and poor prognosis. Wound-healing related myofibroblasts or activated cancer-associated fibroblasts (CAF) are assumed to be the major sources of HA. Both cell types are capable to synthesize new matrix components as well as reorganize the extracellular matrix. However, to which extent myofibroblasts and CAF perform these actions are still unclear. In this work, we investigated the matrix remodeling and HA production potential in normal human dermal fibroblasts (NHFB) and CAF in the absence and presence of transforming growth factor beta -1 (TGF-ß1), with TGF-ß1 being a major factor of regulating fibroblast differentiation. Three-dimensional (3D) collagen matrix was utilized to mimic the extracellular matrix of the tumor microenvironment. We found that CAF appeared to response insensitively towards TGF-ß1 in terms of cell proliferation and matrix remodeling when compared to NHFB. In regards of HA production, we found that both cell types were capable to produce matrix bound HA, rather than a soluble counterpart, in response to TGF-ß1. However, activated CAF demonstrated higher HA production when compared to myofibroblasts. The average molecular weight of produced HA was found in the range of 480 kDa for both cells. By analyzing gene expression of HA metabolizing enzymes, namely hyaluronan synthase (HAS1-3) and hyaluronidase (HYAL1-3) isoforms, we found expression of specific isoforms in dependence of TGF-ß1 present in both cells. In addition, HAS2 and HYAL1 are highly expressed in CAF, which might contribute to a higher production and degradation of HA in CAF matrix. Overall, our results suggested a distinct behavior of NHFB and CAF in 3D collagen matrices in the presence of TGF-ß1 in terms of matrix remodeling and HA production pointing to a specific impact on tumor modulation.

3D Scaffold-Based Macrophage Fibroblast Coculture Model Reveals IL-10 Dependence of Wound Resolution Phase.

Persistent inflammation and impaired repair in dermal wound healing are frequently associated with cell-cell and cell-matrix miscommunication. A direct coculture model of primary human myofibroblasts (MyoFB) and M-CSF-differentiated macrophages (M-Mɸ) in fibrillar three-dimensional Collagen I (Coll I) matrices is developed to study intercellular interactions. The coculture experiments reveal the number of M-Mɸ regulated MyoFB dedifferentiation in a dose-dependent manner. The amount of MyoFB decreases in dependence of the number of cocultured M-Mɸ, even in the presence of MyoFB-inducing transforming growth factor ß1 (TGF-ß1 ). Gene expression analysis of matrix proteins (collagen I, collagen III, ED-A-fibronectin) confirms the results of an altered MyoFB phenotype. Additionally, M-Mɸ is shown to be the main source of secreted cytokine interleukin-10 (IL-10), which is suggested to affect MyoFB dedifferentiation. These findings indicate a paracrine impact of IL-10 secretion by M-Mɸ on the MyoFB differentiation status counteracting the TGF-ß1 -driven MyoFB activation. Hence, the in vitro coculture model simulates physiological situations during wound resolution and underlines the importance of paracrine IL-10 signals by M-Mɸ. In sum, the 3D Coll I-based matrices with a MyoFB-M-Mɸ coculture form a highly relevant biomimetic model of late stages of wound healing.

Influence of hyaluronic acid binding on the actin cortex measured by optical forces.

Melanoma cells are often surrounded by hyaluronic acid (HA) rich environments, which are considered to promote tumor progression and metastasis. Induced effects in compound materials consisting of cells embedded in an extracellular matrix have been studied, however, alterations of the single cells have never been addressed. Here, we explicitly addressed single cell properties and measured HA-induced biomechanical changes via deformations induced solely by optical forces. With the optical stretcher setup, cells were deformed after culturing them in either the presence or absence of HA revealing the crucial interplay of HA with the CD44 receptor. To assess the role of CD44 in transducing effects of HA, we compared a CD44 expressing variant of the melanoma cell line RPM-MC to its natural CD44-negative counterpart. Our measurements revealed a significant stiffness change, which we attribute to changes of the actin cytoskeleton.

Biomimetic tissue models reveal the role of hyaluronan in melanoma proliferation and invasion.

Interactions of hyaluronan (HA) and tumor and stromal cells are highly discussed as one of the major contributors in tumor progression and metastasis. The balance of HA in the tissue is highly regulated by two key enzyme classes; hyaluronan synthases (HAS) and hyaluronidases (HYAL). Current reports hint that the HA amount in the tissue is correlated with poor prognosis in melanoma, the most life-threatening skin tumor. In this work, we generated in vivo mouse models with low and high expression of Has2 and used the models for studying melanoma proliferation of the B78D14 melanoma cell line. We found that a strong reduction of HA amount in the skin was correlated to decreased tissue stiffness and a reduction in tumor weight. Since tumor cells have a direct contact to the HA in the tumor and at the stroma interface, we reconstituted different biomimetic in vitro models using fibroblasts derived from a mouse model to recapitulate melanoma cell behavior at the tumor boundary, namely, (i) decellularized fibroblast matrix (FbECM), (ii) fibroblast embedded into 3D collagen matrices (FbColl), and (iii) well-defined HA-functionalized 3D collagen matrices (HAColl). We found no considerable effect of high and low amounts of fibroblast-derived HA in the matrices on melanoma proliferation and invasion. However, HYAL1-treated FbECM and FbColl, as well as HAColl functionalized with low molecular weight HA (34 kDa) promoted proliferation and invasion of melanoma cells in a concentration dependent manner. Our results emphasize the molecular weight specific effects of HA in regulation of melanoma behavior and provide an alternative explanation for the in vivo observation of HA dependent tumor growth.

Thy-1: more than a marker for mesenchymal stromal cells.

Balanced differentiation of mesenchymal stromal cells (MSCs) into osteoblasts and adipocytes is essential for healthy bone and fat homeostasis. A disturbed balance of MSC differentiation results in bone loss and increased adipogenesis as observed in several human conditions, such as osteoporosis, obesity, and aging. This reflects the importance of MSC fate decision. Therefore, it is important to identify factors that regulate the balance between osteogenic and adipogenic differentiation of MSCs so as to identify new targets to improve bone formation in osteoporosis and control adipose tissue development. There is accumulating evidence that thymus cell antigen 1 (Thy-1), also known as CD90, expressed on MSCs, plays a critical role in the fate decision of MSCs. Recently, Thy-1 has been shown to promote osteogenic differentiation of MSCs and thus bone formation while inhibiting adipogenic differentiation and restricting adipose tissue accumulation. The clinical importance of these findings was validated by the detection of reduced serum soluble Thy-1 in patients with disturbed bone remodeling. In this review, we aim to summarize data on the impact of Thy-1 on the control of MSC differentiation and its consequences for bone and fat formation.-Saalbach, A., Anderegg, U. Thy-1: more than a marker for mesenchymal stromal cells.

Hyaluronan/collagen hydrogels containing sulfated hyaluronan improve wound healing by sustained release of heparin-binding EGF-like growth factor.

Functional biomaterials that are able to bind, stabilize and release bioactive proteins in a defined manner are required for the controlled delivery of such to the desired place of action, stimulating wound healing in health-compromised patients. Glycosaminoglycans (GAG) represent a very promising group of components since they may be functionally engineered and are well tolerated by the recipient tissues due to their relative immunological inertness. Ligands of the Epidermal Growth Factor (EGF) receptor (EGFR) activate keratinocytes and dermal fibroblasts and, thus, contribute to skin wound healing. Heparin-binding EGF-like growth factor (HB-EGF) bound to GAG in biomaterials (e.g. hydrogels) might serve as a reservoir that induces prolonged activation of the EGF receptor and to recover disturbed wound healing. Based on previous findings, the capacity of hyaluronan (HA) and its sulfated derivatives (sHA) to bind and release HB-EGF from HA/collagen-based hydrogels was investigated. Docking and molecular dynamics analysis of a molecular model of HB-EGF led to the identification of residues in the heparin-binding domain of the protein being essential for the recognition of GAG derivatives. Furthermore, molecular modeling and surface plasmon resonance (SPR) analyses demonstrated that sulfation of HA increases binding strength to HB-EGF thus providing a rationale for the development of sHA-containing hydrogels. In line with computational observations and in agreement with SPR results, gels containing sHA displayed a retarded HB-EGF release in vitro compared to pure HA/collagen gels. Hydrogels containing HA and collagen or a mixture with sHA were shown to bind and release bioactive HB-EGF over at least 72 h, which induced keratinocyte migration, EGFR-signaling and HGF expression in dermal fibroblasts. Importantly, hydrogels containing sHA strongly increased the effectivity of HB-EGF in inducing epithelial tip growth in epithelial wounds shown in a porcine skin organ culture model. These findings suggest that hydrogels containing HA and sHA can be engineered for smart and effective wound dressings. STATEMENT OF SIGNIFICANCE: Immobilization and sustained release of recombinant proteins from functional biomaterials might overcome the limited success of direct application of non-protected solute growth factors during the treatment of impaired wound healing. We developed HA/collagen-based hydrogels supplemented with acrylated sulfated HA for binding and release of HB-EGF. We analyzed the molecular basis of HB-EGF interaction with HA and its chemical derivatives by in silico modeling and surface plasmon resonance. These hydrogels bind HB-EGF reversibly. Using different in vitro assays and organ culture we demonstrate that the introduction of sulfated HA into the hydrogels significantly increases the effectivity of HB-EGF action on target cells. Therefore, sulfated HA-containing hydrogels are promising functional biomaterials for the development of mediator releasing wound dressings.

Orf virus infection of human keratinocytes and dermal fibroblasts: Limited virus detection and interference with intercellular adhesion molecule-1 up-regulation.

Orf virus (Parapoxvirus ovis, ORFV) is a dermatotropic virus causing pustular dermatitis in small ruminants and humans. We analysed isolated human primary keratinocytes (KC) and dermal fibroblasts (FB) for cell death and virus replication by infection with a patient-derived ORFV isolate. ORFV infection was associated with rapid induction of cell death in KC allowing for considerable virus removal. Upon infection with ORFV, KC and FB harboured intracytoplasmic ORFV and showed viral protein presence; however, missing virus spread indicated an abortive infection. Upon ORFV exposure, KC but not FB secreted the pro-inflammatory cytokine interleukin (IL)-6. ORFV infection enhanced the frequency of KC expressing intercellular adhesion molecule (ICAM)-1 which was independent of IL-6. Interestingly, ORFV inhibited ICAM-1 up-regulation on infected but not on non-infected KC. Even interferon-γ, a potent inducer of ICAM-1, up-regulated ICAM-1 only on non-infected KC. Transfer of ORFV-free supernatant from infected to non-infected KC induced ICAM-1 on non-infected KC pointing to the involvement of soluble mediator(s). Similarly as in KC, in FB interference with ICAM-1 up-regulation by ORFV infection was also observed. In conclusion, we shed light on epidermal and dermal defense mechanisms to ORFV infection and point to a novel ICAM-1-related immune evasion mechanism of ORFV in human skin.

Thy-1 Deficiency Augments Bone Loss in Obesity by Affecting Bone Formation and Resorption.

Healthy bone remodeling results from a balanced bone formation and bone resorption realized by bone-forming osteoblasts and bone-resorbing osteoclasts, respectively. Recently, Thy-1 (CD90) was identified as positive regulator of osteoblast differentiation and activation, thus, promoting bone formation while concurrently inhibiting adipogenesis and obesity in mice. Additionally, Thy-1 did not affect bone resorption. An obesity-related co-morbidity that is increasing in prevalence is a disturbed bone formation resulting in an increased fracture risk. The underlying mechanisms of obesity-induced bone alterations are not yet fully elucidated and therefore therapy options for efficient bone-anabolic treatments are limited. Therefore, we investigated the impact of Thy-1 on bone metabolism under obese conditions. Indeed, high fat diet (HFD) induced obese mice lacking Thy-1 (Thy-1-/-) showed increased body fat mass compared to wildtype (WT) mice while bone mass (-38%) and formation (-57%) were decreased as shown by micro-computed tomography (µCT) measurement, histological analysis, and fourier-transform infrared spectroscopy (FTIR). Interestingly, under obese conditions, lack of Thy-1 affected both osteoblast and osteoclast function. Number (-30%) and activity of osteoblasts were decreased in obese Thy-1-/- mice while osteoclast number (+39%) and activity were increased. Facilitated bone marrow fat accumulation (+56%) in obese Thy-1-/- mice compared to obese WT mice was associated with upregulated tumor necrosis factor α (Tnfα, +46%) and colony stimulating factor 1 receptor (Csf1r) expression, strong promoters of osteoclast differentiation. Moreover, lack of Thy-1 was accompanied by a reduction of osteoprotegerin (Tnfrsf11b) expression (-36%), an inhibitor of osteoclast differentiation. Altered Tnfα, Csf1r, and Tnfrsf11b expression might be responsible for elevated osteoclast activity in obese Thy-1-deficient mice. In summary, our findings show that lack of Thy-1 promotes obesity under HFD conditions while concurrently decreasing bone mass and formation. Mechanistic studies revealed that under obese conditions lack of Thy-1 impairs both bone formation and bone resorption.

Thy-1 (CD90) promotes bone formation and protects against obesity.

Osteoporosis and obesity result from disturbed osteogenic and adipogenic differentiation and present emerging challenges for our aging society. Because of the regulatory role of Thy-1 in mesenchyme-derived fibroblasts, we investigated the impact of Thy-1 expression on mesenchymal stem cell (MSC) fate between osteogenic and adipogenic differentiation and consequences for bone formation and adipose tissue development in vivo. MSCs from Thy-1-deficient mice have decreased osteoblast differentiation and increased adipogenic differentiation compared to MSCs from wild-type mice. Consistently, Thy-1-deficient mice exhibited decreased bone volume and bone formation rate with elevated cortical porosity, resulting in lower bone strength. In parallel, body weight, subcutaneous/epigonadal fat mass, and bone fat volume were increased. Thy-1 deficiency was accompanied by reduced expression of specific Wnt ligands with simultaneous increase of the Wnt inhibitors sclerostin and dickkopf-1 and an altered responsiveness to Wnt. We demonstrated that disturbed bone remodeling in osteoporosis and dysregulated adipose tissue accumulation in patients with obesity were mirrored by reduced serum Thy-1 concentrations. Our findings provide new insights into the mutual regulation of bone formation and obesity and open new perspectives to monitor and to interfere with the dysregulated balance of adipogenesis and osteogenesis in obesity and osteoporosis.

High-Fat Diet Exacerbates Early Psoriatic Skin Inflammation Independent of Obesity: Saturated Fatty Acids as Key Players.

In obesity, hypertrophic adipocytes secrete high amounts of adipocytokines, resulting in low-grade inflammation amplified by infiltrating proinflammatory macrophages, oxidative stress, hypoxia, and lipolysis. These chronic proinflammatory conditions support the development of type II diabetes and cardiovascular diseases, but the mechanisms of obesity-related exacerbation of inflammatory skin disorders like psoriasis are unclear. In this study, we uncovered dietary saturated fatty acids (SFAs) as major risk factors for the amplification of skin inflammation, independent of obesity-related parameters such as fat mass extension, adipocytokine levels, and glucose homeostasis. Correlation analyses in a cohort of psoriasis vulgaris patients showed that free fatty acid serum level was the only obesity-associated parameter affecting disease severity. Studies in mice with high-fat diet-induced obesity with psoriasiform inflammation confirmed this critical role of free fatty acids. An increase of free fatty acids in healthy, lean mice alone was sufficient to induce an exacerbation of psoriasiform inflammation. In particular, saturated fatty acids sensitize myeloid cells to an increased inflammatory response in answer to proinflammatory stimuli, which in turn augments the activation of keratinocytes. Consequently, reduction of nutritional saturated fatty acids alone diminished the psoriatic phenotype in obese mice. Thus, our findings may open new perspectives for adjuvant dietary measures accompanying anti-inflammatory psoriasis therapies in lean and obese patients.