Complement C5 regulates the expression of insulin-like growth factor binding proteins in chronic experimental allergic encephalomyelitis

RGC-32 Acts as a Hub to Regulate the Transcriptomic Changes Associated With Astrocyte Development and Reactive Astrocytosis

Response Gene to Complement 32 (RGC-32) is an important mediator of the TGF-β signaling pathway, and an increasing amount of evidence implicates this protein in regulating astrocyte biology. We showed recently that spinal cord astrocytes in mice lacking RGC-32 display an immature phenotype reminiscent of progenitors and radial glia, with an overall elongated morphology, increased proliferative capacity, and increased expression of progenitor markers when compared to their wild-type (WT) counterparts that make them incapable of undergoing reactive changes during the acute phase of experimental autoimmune encephalomyelitis (EAE). Here, in order to decipher the molecular networks underlying RGC-32's ability to regulate astrocytic maturation and reactivity, we performed next-generation sequencing of RNA from WT and RGC-32 knockout (KO) neonatal mouse brain astrocytes, either unstimulated or stimulated with the pleiotropic cytokine TGF-β. Pathway enrichment analysis showed that RGC-32 is critical for the TGF-β-induced up-regulation of transcripts encoding proteins involved in brain development and tissue remodeling, such as axonal guidance molecules, transcription factors, extracellular matrix (ECM)-related proteins, and proteoglycans. Our next-generation sequencing of RNA analysis also demonstrated that a lack of RGC-32 results in a significant induction of WD repeat and FYVE domain-containing protein 1 (Wdfy1) and stanniocalcin-1 (Stc1). Immunohistochemical analysis of spinal cords isolated from normal adult mice and mice with EAE at the peak of disease showed that RGC-32 is necessary for the in vivo expression of ephrin receptor type A7 in reactive astrocytes, and that the lack of RGC-32 results in a higher number of homeodomain-only protein homeobox (HOPX)+ and CD133+ radial glia cells. Collectively, these findings suggest that RGC-32 plays a major role in modulating the transcriptomic changes in astrocytes that ultimately lead to molecular programs involved in astrocytic differentiation and reactive changes during neuroinflammation.

RGC-32 Regulates Generation of Reactive Astrocytes in Experimental Autoimmune Encephalomyelitis

Astrocytes are increasingly recognized as critical contributors to multiple sclerosis pathogenesis. We have previously shown that lack of Response Gene to Complement 32 (RGC-32) alters astrocyte morphology in the spinal cord at the peak of experimental autoimmune encephalomyelitis (EAE), suggesting a role for RGC-32 in astrocyte differentiation. In this study, we analyzed the expression and distribution of astrocytes and astrocyte progenitors by immunohistochemistry in spinal cords of wild-type (WT) and RGC-32-knockout (KO) mice with EAE and of normal adult mice. Our analysis showed that during acute EAE, WT astrocytes had a reactive morphology and increased GFAP expression, whereas RGC-32 KO astrocytes had a morphology similar to that of radial glia and an increased expression of progenitor markers such as vimentin and fatty acid binding protein 7 (FABP7). In control mice, GFAP expression and astrocyte density were also significantly higher in the WT group, whereas the number of vimentin and FABP7-positive radial glia was significantly higher in the RGC-32 KO group. In vitro studies on cultured neonatal astrocytes from WT and RGC-32 KO mice showed that RGC-32 regulates a complex array of molecular networks pertaining to signal transduction, growth factor expression and secretion, and extracellular matrix (ECM) remodeling. Among the most differentially expressed factors were insulin-like growth factor 1 (IGF1), insulin-like growth factor binding proteins (IGFBPs), and connective tissue growth factor (CTGF); their expression was downregulated in RGC-32-depleted astrocytes. The nuclear translocation of STAT3, a transcription factor critical for astrogliogenesis and driving glial scar formation, was also impaired after RGC-32 silencing. Taken together, these data suggest that RGC-32 is an important regulator of astrocyte differentiation during EAE and that in the absence of RGC-32, astrocytes are unable to fully mature and become reactive astrocytes.

Proteomic Analysis of CSF from Patients with Leptomeningeal Melanoma Metastases Identifies Signatures Associated with Disease Progression and Therapeutic Resistance

PURPOSE

The development of leptomeningeal melanoma metastases (LMM) is a rare and devastating complication of the late-stage disease, for which no effective treatments exist. Here, we performed a multi-omics analysis of the cerebrospinal fluid (CSF) from patients with LMM to determine how the leptomeningeal microenvironment shapes the biology and therapeutic responses of melanoma cells.

EXPERIMENTAL DESIGN

A total of 45 serial CSF samples were collected from 16 patients, 8 of these with confirmed LMM. Of those with LMM, 7 had poor survival (<4 months) and one was an extraordinary responder (still alive with survival >35 months). CSF samples were analyzed by mass spectrometry and incubated with melanoma cells that were subjected to RNA sequencing (RNA-seq) analysis. Functional assays were performed to validate the pathways identified.

RESULTS

Mass spectrometry analyses showed the CSF of most patients with LMM to be enriched for pathways involved in innate immunity, protease-mediated damage, and IGF-related signaling. All of these were anticorrelated in the extraordinary responder. RNA-seq analysis showed CSF to induce PI3K/AKT, integrin, B-cell activation, S-phase entry, TNFR2, TGFβ, and oxidative stress responses in the melanoma cells. ELISA assays confirmed that TGFβ expression increased in the CSF of patients progressing with LMM. CSF from poorly responding patients conferred tolerance to BRAF inhibitor therapy in apoptosis assays.

CONCLUSIONS

These analyses identified proteomic/transcriptional signatures in the CSF of patients who succumbed to LMM. We further showed that the CSF from patients with LMM has the potential to modulate BRAF inhibitor responses and may contribute to drug resistance.See related commentary by Glitza Oliva and Tawbi, p. 2083.

Histone Deacetylase SIRT1 Mediates C5b-9-Induced Cell Cycle in Oligodendrocytes

Sublytic levels of C5b-9 increase the survival of oligodendrocytes (OLGs) and induce the cell cycle. We have previously observed that SIRT1 co-localizes with surviving OLGs in multiple sclerosis (MS) plaques, but it is not yet known whether SIRT1 is involved in OLGs survival after exposure to sublytic C5b-9. We have now investigated the role of SIRT1 in OLGs differentiation and the effect of sublytic levels of C5b-9 on SIRT1 and phosphorylated-SIRT1 (Ser27) expression. We also examined the downstream effects of SIRT1 by measuring histone H3 lysine 9 trimethylation (H3K9me3) and the expression of cyclin D1 as a marker of cell cycle activation. OLG progenitor cells (OPCs) purified from the brain of rat pups were differentiated in vitro and treated with sublytic C5b-9 or C5b6. To investigate the signaling pathway activated by C5b-9 and required for SIRT1 expression, we pretreated OLGs with a c-jun antisense oligonucleotide, a phosphoinositide 3-kinase (PI3K) inhibitor (LY294002), and a protein kinase C (PKC) inhibitor (H7). Our data show a significant reduction in phospho-SIRT1 and SIRT1 expression during OPCs differentiation, associated with a decrease in H3K9me3 and a peak of cyclin D1 expression in the first 24 h. Stimulation of OLGs with sublytic C5b-9 resulted in an increase in the expression of SIRT1 and phospho-SIRT1, H3K9me3, cyclin D1 and decreased expression of myelin-specific genes. C5b-9-stimulated SIRT1 expression was significantly reduced after pretreatment with c-jun antisense oligonucleotide, H7 or LY294002. Inhibition of SIRT1 with sirtinol also abolished C5b-9-induced DNA synthesis. Taken together, these data show that induction of SIRT1 expression by C5b-9 is required for cell cycle activation and is mediated through multiple signaling pathways.

RGC-32 regulates reactive astrocytosis and extracellular matrix deposition in experimental autoimmune encephalomyelitis

Extracellular matrix (ECM) deposition in active demyelinating multiple sclerosis (MS) lesions may impede axonal regeneration and can modify immune reactions. Response gene to complement (RGC)-32 plays an important role in the mediation of TGF-β downstream effects, but its role in gliosis has not been investigated. To gain more insight into the role played by RGC-32 in gliosis, we investigated its involvement in TGF-β-induced ECM expression and the upregulation of the reactive astrocyte markers α-smooth muscle actin (α-SMA) and nestin. In cultured neonatal rat astrocytes, collagens I, IV, and V, fibronectin, α-SMA, and nestin were significantly induced by TGF-β stimulation, and RGC-32 silencing resulted in a significant reduction in their expression. Using astrocytes isolated from RGC-32 knock-out (KO) mice, we found that the expression of TGF-β-induced collagens I, IV, and V, fibronectin, and α-SMA was significantly reduced in RGC-32 KO mice when compared with wild-type (WT) mice. SIS3 inhibition of Smad3 phosphorylation was also associated with a significant reduction in RGC-32 nuclear translocation and TGF-β-induced collagen I expression. In addition, during experimental autoimmune encephalomyelitis (EAE), RGC-32 KO mouse astrocytes displayed an elongated, bipolar phenotype, resembling immature astrocytes and glial progenitors whereas those from WT mice had a reactive, hypertrophied phenotype. Taken together, our data demonstrate that RGC-32 plays an important role in mediating TGF-β-induced reactive astrogliosis in EAE. Therefore, RGC-32 may represent a new target for therapeutic intervention in MS.

RGC-32 Promotes Th17 Cell Differentiation and Enhances Experimental Autoimmune Encephalomyelitis

Th17 cells play a critical role in autoimmune diseases, including multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis. Response gene to complement (RGC)-32 is a cell cycle regulator and a downstream target of TGF-β that mediates its profibrotic activity. In this study, we report that RGC-32 is preferentially upregulated during Th17 cell differentiation. RGC-32^-/- mice have normal Th1, Th2, and regulatory T cell differentiation but show defective Th17 differentiation in vitro. The impaired Th17 differentiation is associated with defects in IFN regulatory factor 4, B cell-activating transcription factor, retinoic acid-related orphan receptor γt, and SMAD2 activation. In vivo, RGC-32^-/- mice display an attenuated experimental autoimmune encephalomyelitis phenotype accompanied by decreased CNS inflammation and reduced frequency of IL-17- and GM-CSF-producing CD4⁺ T cells. Collectively, our results identify RGC-32 as a novel regulator of Th17 cell differentiation in vitro and in vivo and suggest that RGC-32 is a potential therapeutic target in multiple sclerosis and other Th17-mediated autoimmune diseases.

RGC-32 is a novel regulator of the T-lymphocyte cell cycle

We have previously shown that RGC-32 is involved in cell cycle regulation in vitro. To define the in vivo role of RGC-32, we generated RGC-32 knockout mice. These mice developed normally and did not spontaneously develop overt tumors. To assess the effect of RGC-32 deficiency on cell cycle activation in T cells, we determined the proliferative rates of CD4(+) and CD8(+) T cells from the spleens of RGC-32(-/-) mice, as compared to wild-type (WT, RGC-32(+/+)) control mice. After stimulation with anti-CD3/anti-CD28, CD4(+) T cells from RGC-32(-/-) mice displayed a significant increase in [(3)H]-thymidine incorporation when compared to WT mice. In addition, both CD4(+) and CD8(+) T cells from RGC-32(-/-) mice displayed a significant increase in the proportion of proliferating Ki67(+) cells, indicating that in T cells, RGC-32 has an inhibitory effect on cell cycle activation induced by T-cell receptor/CD28 engagement. Furthermore, Akt and FOXO1 phosphorylation induced in stimulated CD4(+) T-cells from RGC-32(-/-) mice were significantly higher, indicating that RGC-32 inhibits cell cycle activation by suppressing FOXO1 activation. We also found that IL-2 mRNA and protein expression were significantly increased in RGC-32(-/-) CD4(+) T cells when compared to RGC-32(+/+) CD4(+) T cells. In addition, the effect of RGC-32 on the cell cycle and IL-2 expression was inhibited by pretreatment of the samples with LY294002, indicating a role for phosphatidylinositol 3-kinase (PI3K). Thus, RGC-32 is involved in controlling the cell cycle of T cells in vivo, and this effect is mediated by IL-2 in a PI3K-dependent fashion.

Dual role of Response gene to complement-32 in multiple sclerosis

Response gene to complement (RGC)-32 is a novel molecule that plays an important role in cell proliferation. We investigated the expression of RGC-32 in multiple sclerosis (MS) brain and in peripheral blood mononuclear cells (PBMCs) obtained from patients with relapsing-remitting multiple sclerosis. We found that CD3(+), CD68(+), and glial fibrillar acidic protein (GFAP)(+) cells in MS plaques co-localized with RGC-32. Our results show a statistically significant decrease in RGC-32 mRNA expression in PBMCs during relapses when compared to the levels in stable MS patients. This decrease might be useful in predicting disease activity in patients with relapsing-remitting MS. RGC-32 expression was also correlated with that of FasL mRNA during relapses. FasL mRNA expression was significantly reduced after RGC-32 silencing, indicating a role for RGC-32 in the regulation of FasL expression. In addition, the expression of Akt1, cyclin D1, and IL-21 mRNA was significantly increased during MS relapses when compared to levels in healthy controls. Furthermore, we investigated the role of RGC-32 in TGF-β-induced extracellular matrix expression in astrocytes. Blockage of RGC-32 using small interfering RNA significantly inhibits TGF-β induction of procollagen I, fibronectin and of the reactive astrocyte marker α-smooth muscle actin (α-SMA). Our data suggest that RGC-32 plays a dual role in MS, both as a regulator of T-cells mediated apoptosis and as a promoter of TGF-β-mediated profibrotic effects in astrocytes.

C5b-9-activated, K(v)1.3 channels mediate oligodendrocyte cell cycle activation and dedifferentiation

Voltage-gated potassium (K(v)) channels play an important role in the regulation of growth factor-induced cell proliferation. We have previously shown that cell cycle activation is induced in oligodendrocytes (OLGs) by complement C5b-9, but the role of K(v) channels in these cells had not been investigated. Differentiated OLGs were found to express K(v)1.4 channels, but little K(v)1.3. Exposure of OLGs to C5b-9 modulated K(v)1.3 functional channels and increased protein expression, whereas C5b6 had no effect. Pretreatment with the recombinant scorpion toxin rOsK-1, a highly selective K(v)1.3 inhibitor, blocked the expression of K(v)1.3 induced by C5b-9. rOsK-1 inhibited Akt phosphorylation and activation by C5b-9 but had no effect on ERK1 activation. These data strongly suggest a role for K(v)1.3 in controlling the Akt activation induced by C5b-9. Since Akt plays a major role in C5b-9-induced cell cycle activation, we also investigated the effect of inhibiting K(v)1.3 channels on DNA synthesis. rOsK-1 significantly inhibited the DNA synthesis induced by C5b-9 in OLG, indicating that K(v)1.3 plays an important role in the C5b-9-induced cell cycle. In addition, C5b-9-mediated myelin basic protein and proteolipid protein mRNA decay was completely abrogated by inhibition of K(v)1.3 expression. In the brains of multiple sclerosis patients, C5b-9 co-localized with NG2(+) OLG progenitor cells that expressed K(v)1.3 channels. Taken together, these data suggest that K(v)1.3 channels play an important role in controlling C5b-9-induced cell cycle activation and OLG dedifferentiation, both in vitro and in vivo.

Cancer and the complement cascade

Despite significant research on the role of inflammation and immunosurveillance in the immunologic microenvironment of tumors, little attention has been given to the oncogenic capabilities of the complement cascade. The recent finding that complement may contribute to tumor growth suggests an insidious relationship between complement and cancer, especially in light of evidence that complement facilitates cellular proliferation and regeneration. We address the hypothesis that complement proteins promote carcinogenesis and suggest mechanisms by which complement can drive the fundamental features of cancer. Evidence shows that this diverse family of innate immune proteins facilitates dysregulation of mitogenic signaling pathways, sustained cellular proliferation, angiogenesis, insensitivity to apoptosis, invasion and migration, and escape from immunosurveillance. Given that the traditionally held functions for the complement system include innate immunity and cancer defense, our review suggests a new way of thinking about the role of complement proteins in neoplasia.

Complement and the central nervous system: emerging roles in development, protection and regeneration

As expanding research reveals the novel ability of complement proteins to promote proliferation and regeneration of tissues throughout the body, the concept of the complement cascade as an innate immune effector has changed rapidly. In particular, its interactions with the central nervous system have provided a wealth of information regarding the ability of complement proteins to mediate neurogenesis, synaptogenesis, cell migration, neuroprotection, proliferation and regeneration. At numerous phases of the neuronal and glial cell cycle, complement proteins exert direct or indirect influence over their behavior and fate. Neuronal stem cells differentiate and migrate in response to complement, and it prevents injury and death in adult cells in response to toxic agents. Furthermore, complement proteins promote survival via anti-apoptotic actions, and can facilitate clearance and regeneration of injured tissues in various models of CNS disease. In summary, we highlight the protean abilities of complement proteins in the central nervous system, underscoring an exciting avenue of research that has yielded greater understanding of complement's role in central nervous system health and disease.

Epigenetic modifications induced by RGC-32 in colon cancer

First described as a cell cycle activator, RGC-32 is both an activator and a substrate for CDC2. Deregulation of RGC-32 expression has been detected in a wide variety of human cancers. We have now shown that RGC-32 is expressed in precancerous states, and its expression is significantly higher in adenomas than in normal colon tissue. The expression of RGC-32 was higher in advanced stages of colon cancer than in precancerous states or the initial stages of colon cancer. In order to identify the genes that are regulated by RGC-32, we used gene array analysis to investigate the effect of RGC-32 knockdown on gene expression in the SW480 colon cancer cell line. Of the 230 genes that were differentially regulated after RGC-32 knockdown, a group of genes involved in chromatin assembly were the most significantly regulated in these cells: RGC-32 knockdown induced an increase in acetylation of histones H2B lysine 5 (H2BK5), H2BK15, H3K9, H3K18, and H4K8. RGC-32 silencing was also associated with decreased expression of SIRT1 and decreased trimethylation of histone H3K27 (H3K27me3). In addition, RGC-32 knockdown caused a significantly higher percentage of SW480 cells to enter S phase and subsequently G2/M. These data suggest that RGC-32 may contribute to the development of colon cancer by regulating chromatin assembly.

Neuroprotective effects of the complement terminal pathway during demyelination: implications for oligodendrocyte survival

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system that is mediated by activated lymphocytes, macrophages/microglia, and complement. In MS, the myelin-forming oligodendrocytes (OLGs) are the targets of the immune attack. Experimental evidence indicates that C5b-9 plays a role in demyelination during the acute phase of experimental allergic encephalomyelitis (EAE). Terminal complement C5b-9 complexes are capable of protecting OLGs from apoptosis. During chronic EAE complement C5 promotes axonal preservation, remyelination and provides protection from gliosis. These findings indicate that the activation of complement and C5b-9 assembly can also have protective roles during demyelination.

Enhancing the ability of experimental autoimmune encephalomyelitis to serve as a more rigorous model of multiple sclerosis through refinement of the experimental design

Advancing the understanding of the mechanisms involved in the pathogenesis of multiple sclerosis (MS) likely will lead to new and better therapeutics. Although important information about the disease process has been obtained from research on pathologic specimens, peripheral blood lymphocytes and MRI studies, the elucidation of detailed mechanisms has progressed largely through investigations using animal models of MS. In addition, animal models serve as an important tool for the testing of putative interventions. The most commonly studied model of MS is experimental autoimmune encephalomyelitis (EAE). This model can be induced in a variety of species and by various means, but there has been concern that the model may not accurately reflect the disease process, and more importantly, it may give rise to erroneous findings when it is used to test possible therapeutics. Several reasons have been given to explain the shortcomings of this model as a useful testing platform, but one idea provides a framework for improving the value of this model, and thus, it deserves careful consideration. In particular, the idea asserts that EAE studies are inadequately designed to enable appropriate evaluation of putative therapeutics. Here we discuss problem areas within EAE study designs and provide suggestions for their improvement. This paper is principally directed at investigators new to the field of EAE, although experienced investigators may find useful suggestions herein.