Browsing by Subject "RIP140"
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Item The functional impact of Retinoic acid and RIP140 in macrophages: from chromatin to physiology(2016-08) Lee, BomiInnate immunity consists of two systems; humoral and cellular systems. The humoral system includes anti-microbial peptides and opsonins while the cellular system involves specialized cells including phagocytes. The major functions of phagocytes are scavenging toxic compounds and producing inflammatory mediators to destroy infectious organisms and to transfer signals to other immune cells. Dysregulation of the phagocytic system by various conditions including the defect of immune cells and insufficient nutrition can lead to inflammatory diseases. Therefore, understanding the characteristics of phagocytes and the molecular mechanism in response to extracellular stimulations is critical for the development of therapeutics for inflammatory diseases. The focus of my thesis was to evaluate cellular signaling and its pathophysiological relationship in one type of phagocytes, macrophages. All-trans retinoic acid (RA) and its derivatives have been proved as potent therapeutics for inflammatory diseases, but the molecular mechanism of RA action in macrophages was not well established. In order to shed light on the functional role of RA in macrophages, I first found that topical application of RA significantly improved wound healing and the co-stimulation with RA and IL-4 synergistically activated Arginase-1 (Arg1), a critical gene for tissue repair, in macrophages. This involves feed forward regulation of Raldh2, a rate-limiting enzyme for RA biosynthesis, and requires Med25 to remodel the +1 nucleosome of Arg1 for transcription initiation and to facilitate transcriptional initiation-elongation coupling by recruiting elongation factor TFIIS. This study demonstrated RA’s modulatory activity in IL-4-induced anti-inflammatory macrophages, which involves synergistic activation of Arg1 by RA and IL-4 and a functional role of Med25 in chromatin remodeling of this gene promoter. In macrophage activation, there are two well-established phenotypes; classically activated (M1, pro-inflammatory) and alternatively activated (M2, anti-inflammatory) macrophages. The switch from M1 to M2 is critical for the control of inflammatory responses including wound repair. Previously, it has been found that Receptor-interacting Protein 140 (RIP140) is an enhancer of M1 by acting as a co-activator for NF-κB. Related to this, my research has uncovered that RIP140 delays the wound healing process by suppressing the macrophage phenotype switch from M1 to M2. With regards to mechanism, IL-4 treatment stimulates RIP140 export from the nucleus to the cytoplasm to form a complex with calpain regulatory subunit (CAPNS1) to activate calpain1/2 that enhances the activity of PTP1B, a negative regulator for STAT6 in M2 macrophages. Together, these results have established a new modulatory role of RIP140 in macrophage phenotype switch during wound healing by regulating both M1 and M2 activations (enhancing M1 and suppressing M2 activation). Another new finding I discovered about RIP140 was its repressive effect on osteoclast (OC) differentiation. OCs are derived from monocyte/macrophage lineage of hematopoietic cells and are responsible for bone resorptive activity. OCs maintain a balance in bone remodeling with osteoblasts (OB) that are involved in bone formation. RIP140 forms a complex with orphan nuclear receptor TR4 in pre-osteoclastic cells to suppress OC differentiation. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL) induces RIP140 protein degradation and represses TR4 mRNA level, which terminates the repressive activity of TR4/RIP140 complex in OC differentiation. In vivo micro CT analysis of macrophage/monocyte-specific RIP140 KD (mϕRIP140KD) mice showed an osteopenia phenotype with reduced OB function and increased OC activity, indicating uncoupling between OC and OB. This study demonstrated RIP140’s additional role in OC differentiation and bone diseases such as osteoporosis. Taken all together, these studies have established fine-tuning molecular mechanisms in macrophages, including their phenotypic switch and polarization/maturation. Specifically, we uncovered additional pathways of signal inputs and stimuli that regulate these processes such as RA, IL-4 and RANKL, and determined their physiological relevance in wound healing, inflammation and osteoclastogenesis. Differential activation of macrophages by these biological cues further confirms the plastic nature of macrophages. These findings contribute to our understanding of signaling mechanisms in macrophage polarization and their impact on diseases.Item Functional role of receptor-interacting protein 140 (RIP140) in adipocyte dysfunctions and inflammatory response in macrophages.(2012-03) Ho, Ping-ChihThe prevalence of metabolic diseases in modern society, including Type II diabetes mellitus (T2DM), hypertension and cardiovascular diseases, is a major burden on health care systems. Among these diseases, T2DM and its associated complications contribute to the progression of other metabolic diseases such as fatty liver diseases and atherosclerosis. Understanding the initiation and progression of T2DM is critical for developing treatments for T2DM and its associated metabolic disorders. Adipocyte dysfunctions and chronic inflammation have been shown recently to play essential roles in the progression of T2DM. Normally, adipocytes can store energy as triglycerides, fine-tune other metabolic tissues¡¦ lipid and glucose metabolism, and secreted cytokines (adipokines) to modulate immune response. In T2DM or obesity, adipocytes become dysfunctional, with increased lipolysis, an altered adipokine profile, and decreased insulin sensitivity and glucose uptake ability. These changes affect not only the adipocytes themself but also systemic glucose and lipid metabolism. In obese patients and in the high-fat diet (HFD)-fed mouse model, increased inflammatory response in macrophages also contributes to adipocyte dysfunction. The escalated inflammatory response plays pathophysiological roles in various metabolic disorders, including atherosclerosis and arthritis, and increases the incidence of septic shock. However, the underlying mechanisms for initiation of adipocyte dysfunctions and escalation of inflammatory response remain unclear. Receptor-interacting protein 140 (RIP140) is a co-regulator for various transcription factors and nuclear receptors and is expressed mainly in macrophages and metabolic tissues, including adipocytes, hepatocytes and muscle cells. RIP140 affects the progression of T2DM through its nuclear activity as shown by the resistance of knockout mice to diet-induced diabetes and its associated metabolic disorders. In my studies, I found that when I used HFD feeding to induce T2DM, RIP140 could accumulate within the cytoplasm of adipocytes. I further demonstrated that cytoplasmic RIP140 not only interacted with AS160 to impede GLUT4 vesicle trafficking and adiponectin vesicle secretion, but also formed a complex with perilipin A to enhance lipolysis. These findings suggest that HFD feeding can alter RIP140¡¦s cellular distribution, which leads to adipocyte dysfunctions including higher lipolysis, lower glucose uptake, and reduction in adiponectin secretion. I also showed that HFD feeding promoted cytoplasmic accumulation of RIP140 in adipocytes through a PKCϵ-dependent signaling pathway by enhancing intracellular lipid content (as an intrinsic stimulus) and circulating endothelin-1 (as an extrinsic stimulus). Most importantly, administration of a selective ET-1 receptor anatagonist, ambrisentan, reduced HFD-induced cytoplasmic accumulation of RIP140 in adipocytes and further ameliorate hepatic steatosis and insulin sensitivity in vivo. These findings reveal the novel roles of cytoplasmic RIP140 in adipocyte dysfunctions and provide evidence for cytoplasmic RIP140 as a promising target for treatment of T2DM. Recently, RIP140 has also been shown to affect proinflammatory cytokine production by functioning as co-activator for NF-fÛB in macrophages. I showed that HFD feeding up-regulated RIP140 expression by promoting intracellular cholesterol level which led to increased proinflammatory potential in macrophages. In this study, intracellular cholesterol level regulates RIP140 expression by decreasing microRNA-33a, which targeted RIP140 via a conserved region in 3¡¦-UTR of RIP140 mRNA. I further discovered that TLR ligands could trigger RIP140 degradation to resolve inflammation. This RIP140 degradation was modulated by RelA-recruited SCF E3 ligase and Syk-mediated phosphorylation on RIP140. My studies in macrophages demonstrate that RIP140 in macrophages can be modulated by a HFD to affect the systemic inflammatory response and further suggest that defects in RIP140 degradation may cause non-resolving inflammation which is involved in septic shock and various metabolic disorders. Taken together, my studies provide evidence for the novel functions of RIP140 in adipocyte dysfunction and inflammatory response in macrophages and determine the mechanisms by which HFD affect RIP140¡¦s distribution and expression in adipcoytes and macrophages. These findings contribute to our understanding of how HFD causes adipocyte dysfunctions and increase inflammatory response.Item The Functional Role of Receptor-Interacting Protein 140 (RIP140) in Innate Immunity and Metabolic Syndrome(2016-12) Lin, Yi-WeiMetabolic diseases, such as type II diabetes (T2DM), atherosclerosis and other cardiovascular diseases, are prevalent and are important health issues in the modern world. T2DM contributes to the development of various metabolic diseases. Atherosclerosis is one of the major causes leading to multiple cardiovascular diseases. In order to develop therapeutic strategies, understanding the mechanisms of these metabolic diseases is crucial. It is known that the immune system is highly involved in initiation and progression of metabolic diseases. Macrophages are one of the major leukocytes in innate immunity. Macrophages have two major polarized phenotypes: classical/pro-inflammatory (M1) and alternative/anti-inflammatory (M2). It is widely accepted that M1-M2 switch in macrophage population is essential in disease progression or damage recovery; however, the detailed mechanism of macrophage phenotype switch has not been fully elucidated. In addition, the effect of altering the macrophage phenotype on treating metabolic diseases remains uncertain. Receptor-interacting protein 140 (RIP140) is a co-regulator of numerous nuclear receptors and transcription factors. RIP140 is expressed in various cell types including adipocytes, liver, muscle, heart, neurons, and cells in the monocyte–macrophage lineage. Studies showed that RIP140 expression is positively associated with the progression of metabolic disorders such as obesity, insulin resistance, and glucose intolerance. In addition, studies indicate that RIP140 acts as a co-activator of NFκB to promote macrophage M1 activation and pro-inflammatory responses. My studies further build on this knowledge to uncover the role of RIP140 in the metabolic diseases. First, it was found that RIP140 elevates cholesterol content in macrophages by reducing expression of ABC transporters, which are responsible for cholesterol efflux. The elevated cytosolic cholesterol induces foam cell formation and further enhances progression of atherosclerosis. This study indicated that reducing RIP140 levels effectively ameliorates high-cholesteroldiet-induced atherosclerosis. Second, my study found that reducing RIP140 in macrophages leads to macrophage M2 polarization, resulting in adipose tissue remodeling to brown/beige adipose tissue. This further ameliorates high fat diet-induced T2DM associated metabolic disorders. Moreover, later studies address how RIP140 mediates macrophage M2 activation and M1/M2 switch by its cytosolic function in a wound healing animal model. Final study is to identify a beneficial taxonomic repertoire from macrophage specific RIP140 knockdown (MφRIP140KD) mice. Fecal microbiota transplantation (FMT) from HFD-fed MφRIP140KD to wild type (WT) mice acquired the benefits from donors, which is resistant to development of HFD-induced metabolic diseases. Taken together, this thesis studies elucidate novel functions of RIP140 in polarization and inflammatory responses in macrophages, and identify the benefits of reducing RIP140 expression in macrophages. These findings contribute to our understanding of the relationship between immune and metabolic systems as well as provide a therapeutic target of resolving inflammation and preventing/improving metabolic profiles in T2DM, and atherosclerosis.