Effect of human very low-density lipoproteins on cardiotrophin-like cytokine factor 1 (CLCF1) activity

Detection of CLCF1 protein expression by flow cytometry

Cardiotrophin-like cytokine factor 1 (CLCF1) is an IL-6 family cytokine with neurotrophic and immuno-modulating functions. CLCF1 mRNA has been detected in primary and secondary lymphoid organs, and up-regulation of CLCF1 mRNA levels has been associated with the T helper (Th) 17 polarization. However, information regarding CLCF1 expression by immune cells at the protein level remains scarce. We have developed a methodology that uses a monoclonal antibody (mAb) directed against CLCF1 for the detection of human and mouse CLCF1 by flow cytometry. We have successfully detected CLCF1 protein expression in cells from the mouse pro-B cell line Ba/F3 that were transduced with CLCF1 cDNA. Interestingly, we found that the anti-CLCF1 mAb inhibits CLCF1 biological activity in vitro by binding to an epitope that encompasses site III of the cytokine. Moreover, we have detected CLCF1 expression in mouse splenic T cells, as well as in vitro differentiated Th1 cells. The specificity of the fluorescence signal was demonstrated using Clcf1-deficient lymphocytes generated using a conditional knock-out mouse model. The detection of CLCF1 protein by flow cytometry will be a valuable tool to study CLCF1 expression during normal and pathological immune responses.

Post-Translational Modifications of ATG4B in the Regulation of Autophagy

Autophagy plays a key role in eliminating and recycling cellular components in response to stress, including starvation. Dysregulation of autophagy is observed in various diseases, including neurodegenerative diseases, cancer, and diabetes. Autophagy is tightly regulated by autophagy-related (ATG) proteins. Autophagy-related 4 (ATG4) is the sole cysteine protease, and four homologs (ATG4A–D) have been identified in mammals. These proteins have two domains: catalytic and short fingers. ATG4 facilitates autophagy by promoting autophagosome maturation through reversible lipidation and delipidation of seven autophagy-related 8 (ATG8) homologs, including microtubule-associated protein 1-light chain 3 (LC3) and GABA type A receptor-associated protein (GABARAP). Each ATG4 homolog shows a preference for a specific ATG8 homolog. Post-translational modifications of ATG4, including phosphorylation/dephosphorylation, O-GlcNAcylation, oxidation, S-nitrosylation, ubiquitination, and proteolytic cleavage, regulate its activity and ATG8 processing, thus modulating its autophagic activity. We reviewed recent advances in our understanding of the effect of post-translational modification on the regulation, activity, and function of ATG4, the main protease that controls autophagy.

Specific cytokines of interleukin-6 family interact with S100 proteins

Cytokines of interleukin-6 (IL-6) family are important signaling proteins involved in various physiological and pathological processes. Earlier, we described interactions between IL-11 and S100P/B proteins from the family of S100 proteins engaged in the pathogenesis of numerous diseases. We probed here interactions between seven IL-6 family cytokines (IL-6, IL-11, OSM, LIF, CNTF, CT-1, and CLCF1) and fourteen S100 proteins (S100A1/A4/A6/A7/A8/A9/A10/A11/A12/A13/A14/A15/B/P). Surface plasmon resonance spectroscopy revealed formation of calcium-dependent complexes between IL-11, OSM, CNTF, CT-1, and CLCF1 and distinct subsets of S100A1/A6/B/P proteins with equilibrium dissociation constants of 19 nM - 12 µM. The existence of a network of interactions between Ca²⁺-loaded S100 proteins and IL-6 family cytokines suggest regulation of these cytokines by the extracellular forms of S100 proteins.

Cardiotrophin Like Cytokine Factor 1 (CLCF1) alleviates bone loss in osteoporosis mouse models by suppressing osteoclast differentiation through activating interferon signaling and repressing the nuclear factor-κB signaling pathway

A growing body of evidence suggests that immune factors that regulate osteoclast differentiation and bone resorption might be promising therapeutic agents for the treatment of osteoporosis. The expression of CLCF1, an immune cell-derived molecule, has been reported to be reduced in patients with postmenopausal osteoporosis. This suggests that it may be involved in bone remodeling. Thus, we explored the functional role of CLCF1 in osteoclastogenesis and bone loss associated with osteoporosis. Surprisingly, the administration of recombinant CLCF1 repressed excessive bone loss in ovariectomized mice and prevented RANKL-induced bone loss in calvarial mouse model. Likewise, the addition of recombinant CLCF1 to RANKL-stimulated monocytes resulted in a significant suppression in the number of differentiated osteoclasts with small resorption areas being observed on dentine slices in vitro. At the same dosage, CLCF1 did not exhibit any detectable negative effects on the differentiation of osteoblasts. Mechanistically, the inhibition of osteoclast differentiation by the CLCF1 treatment appears to be related to the activation of interferon signaling (IFN) and the suppression of the NF-κB signaling pathway. Interestingly, the expression of the main components of IFN-signaling namely, STAT1 and IRF1, was detected in macrophages as early as 1 h after stimulation with CLCF1. Consistent with these results, the blockade of STAT1 in macrophages abolished the inhibitory effect of CLCF1 on osteoclast differentiation in vitro. These collective findings point to a novel immunoregulatory function of CLCF1 in bone remodeling and highlight it as a potentially useful therapeutic agent for the treatment of osteoporosis.

CNTF Prevents Development of Outer Retinal Neovascularization Through Upregulation of CxCl10

Purpose

Ciliary neurotrophic factor (CNTF) is a well-characterized neurotrophic factor currently in clinical trials for the treatment of macular telangiectasia type II. Our previous work showed that CNTF-induced STAT3 signaling is a potent inhibitor of pathologic preretinal neovascular tuft formation in the mouse model of oxygen-induced retinopathy. In this study, we investigated the effect of CNTF on outer retinal and choroidal angiogenesis and the mechanisms that underpin the observed decrease in outer retinal neovascularization following CNTF treatment.

Methods

In the Vldlr^–/– and laser-CNV mouse models, mice received a one-time injection (on postnatal day [P] 12 in the Vldlr^–/– model and 1 day after laser in the Choroidal Neovascularization (CNV) model) of recombinant CNTF or CxCl10, and the extent of neovascular lesions was assessed 6 days posttreatment. STAT3 downstream targets affected by CNTF treatment were identified using quantitative PCR analysis. A proteome array was used to compare media conditioned by CNTF-treated and control-treated primary Müller cells to screen for CNTF-induced changes in secreted angiogenic factors.

Results

Intravitreal treatment with recombinant CNTF led to significant reduction in neovascularization in the Vldlr^–/– and laser-CNV mouse models. Treatment effect in the Vldlr^–/– was long-lasting but time sensitive, requiring intravitreal treatment before P19. Mechanistic workup in vitro as well as in vivo confirmed significant activation of the STAT3-signaling pathway in Müller cells in response to CNTF treatment and upregulation of CxCl10. Intravitreal injections of recombinant CxCl10 significantly reduced outer retinal neovascularization in vivo in both the Vldlr^–/– and laser-CNV mouse models.

Conclusions

CNTF treatment indirectly affects outer retinal and choroidal neovascularization by inducing CxCl10 secretion from retinal Müller cells.

Cardiotrophin-Like Cytokine Factor 1 Exhibits a Myeloid-Biased Hematopoietic-Stimulating Function

Cardiotrophin-like cytokine factor 1 (CLCF1) is secreted as a complex with the cytokine receptor-like factor 1 (CRLF1). Syndromes caused by mutations in the genes encoding CLCF1 or CRLF1 suggest an important role for CLCF1 in the development and regulation of the immune system. In mice, CLCF1 induces B-cell expansion, enhances humoral responses and triggers autoimmunity. Interestingly, inactivation of CRLF1, which impedes CLCF1 secretion, leads to a marked reduction in the number of bone marrow (BM) progenitor cells, while mice heterozygous for CLCF1 display a significant decrease in their circulating leukocytes. We therefore hypothesized that CLCF1 might be implicated in the regulation of hematopoiesis. To test this hypothesis, murine hematopoietic progenitor cells defined as Lin⁻Sca1⁺c-kit⁺ (LSK) were treated in vitro with ascending doses of CLCF1. The frequency and counts of LSK cells were significantly increased in the presence of CLCF1, which may be mediated by several CLCF1-induced soluble factors including IL-6, G-CSF, IL-1β, IL-10, and VEGF. CLCF1 administration to non-diseased C57BL/6 mice resulted in a pronounced increase in circulating myeloid cells, which was concomitant with augmented LSK and myeloid cell counts in the BM. Likewise, CLCF1 administration to mice following sub-lethal irradiation or congeneic BM transplantation (BMT) resulted in accelerated LSK recovery along with a sustained increase in BM-derived CD11b⁺ cells. Altogether, our observations establish an important and unforeseen role for CLCF1 in regulating hematopoiesis with a bias toward myeloid cell differentiation.

Cardiotrophin-like cytokine (CLCF1) modulates mesenchymal stem cell osteoblastic differentiation

Mesenchymal stem cells (MSCs) are multipotent cells capable of differentiating into adipocytes, chondrocytes, or osteocytes. MSCs secrete an array of cytokines and express the LIFRβ (leukemia inhibitory factor receptor) chain on their surface. Mutations in the gene coding for LIFRβ lead to a syndrome with altered bone metabolism. LIFRβ is one of the signaling receptor chains for cardiotrophin-like cytokine (CLCF1), a neurotrophic factor known to modulate B and myeloid cell functions. We investigated its effect on MSCs induced to differentiate into osteocytes in vitro Our results indicate that CLCF1 binds mouse MSCs, triggers STAT1 and -3 phosphorylation, inhibits the up-regulation of master genes involved in the control of osteogenesis, and markedly prevents osteoblast generation and mineralization. This suggests that CLCF1 could be a target for therapeutic intervention with agents such as cytokine traps or blocking mAbs in bone diseases such as osteoporosis.

The Search for Biomarkers to Aid in Diagnosis, Differentiation, and Prognosis of Childhood Idiopathic Nephrotic Syndrome

Identification of genes associated with childhood-onset nephrotic syndrome has significantly advanced our understanding of the pathogenesis of this complex disease over the past two decades, however the precise etiology in many cases remains unclear. At this time, we still rely on invasive kidney biopsy to determine the underlying cause of nephrotic syndrome in adults. In children, response to steroid therapy has been shown to be the best indicator of prognosis, and therefore all children are treated initially with corticosteroids. Because this strategy exposes a large number of children to the toxicities of steroids without providing any benefit, many researchers have sought to find a marker that could predict a patient's response to steroids at the time of diagnosis. Additionally, the identification of such a marker could provide prognostic information about a patient's response to medications, progression to end stage renal disease, and risk of disease recurrence following transplantation. Major advances have been made in understanding how genetic biomarkers can be used to predict a patient's response to therapies and disease course, especially after transplantation. Research attempting to identify urine- and serum-based biomarkers which could be used for the diagnosis, differentiation, and prognosis of nephrotic syndrome has become an area of emphasis. In this review, we explore the most exciting biomarkers and their potential clinical applications.