Cytokine Profiling in Patients with VCP-Associated Disease

Communications Cytokine Profiling in Patients with VCP-Associated Disease Eric Dec, M.D. 1 , Prachi Rana, B.S. 1 , Veeral Katheria, B.S. 1 , Rachel Dec 1 , Manaswitha Khare, M.D. 1 , Angele Nalbandian, Ph.D. 1 , Szu-Yun Leu, Ph.D. 2 , Shlomit Radom-Aizik, Ph.D. 2 , Katrina Llewellyn, Ph.D. 1 , Lbachir BenMohamed, Ph.D. 3 , Frank Zaldivar, Ph.D. 2 , and Virginia Kimonis, M.D. 1 Abstract Valosin containing protein (VCP) disease (also known as Inclusion Body Myopathy, Paget Disease of Bone and Frontotemporal ­Dementia [IBMPFD] syndrome) is caused by mutations in the gene encoding VCP classically affecting the muscle, bone and brain. Although the genetic cause has been identified, details regarding the pathogenesis of IBMPFD have not been fully determined. Muscle ­wasting observed in VCP disease is suggestive of cytokine imbalance. We hypothesized that dysfunctional protein homeostasis caused by VCP mutations leads to cytokine imbalances thereby contributing to the muscle wasting phenotype. Circulating levels of interleukin-4 (IL-4), interleukin-6 (IL-6), tumor necrosis factor alpha (TNF a) and epidermal growth factor (EGF) were measured in plasma of patients with VCP disease or controls. TNF a and EGF were significantly altered in VCP disease as compared to control. TNF a was up-regulated, ­consistent with a cachexia phenotype and EGF levels were increased. No significant differences were observed in IL-4 and IL-6. Cytokine imbalances may be associated with VCP disease and may play a contributory role in VCP myopathy. Further understanding of how VCP dysfunction leads to aberrant protein homeostasis and subsequent cytokine imbalances may also aid in the understanding of other proteinopathies and in the development of novel treatments. Clin Trans Sci 2014; Volume 7: 29–32 Keywords: IBMPFD, cytokines, VCP Introduction Muscle wasting is found in a multitude of disease states in reaction to a variety of insults. Muscle atrophy can be secondary to disuse, nutritional deficiencies, neuropathy, vasculopathy, cancer, HIV, and other inflammatory diseases. Inflammatory states occur as a result of cytokine release and subsequent activation of the immune response. If levels of pro-inflammatory cytokines are elevated for prolonged periods, muscle wasting can result. The importance of both pro- and anti-inflammatory cytokine balances in maintaining skeletal muscle health is increasingly recognized. Cytokine factors such as interleukin-6 (IL-6) and tumor necrosis factor alpha (TNFα) have long been implicated in muscle wasting. 1,2 In fact, TNFα was once known as cachectin given its direct effect in muscle atrophy. 3 Evidence reported by Horsely et al., 4 suggests interleukin-4 (IL-4) plays a role in myoblast fusion and myogenesis and epidermal growth factor (EGF) has been a key component in most commercially available myoblast media since 1992 5 although its specific role in myogenesis is unclear. Regarding inflammatory pathways, it is especially enticing to consider the role of inflammation in Valosin containing protein (VCP) disease given the progressive muscle cachexia. VCP disease, also known as Inclusion Body Myopathy, Paget’s Disease of Bone and Frontotemporal Dementia (IBMPFD), is a life shortening, crippling disease of muscle, bone and brain. 6 It is an autosomal dominant, adult onset disease caused by mutations in the VCP gene. 6 VCP is an ATP driven shuttling/chaperone protein that normally participates in protein homeostasis through its interaction with degradative pathways including the ubiquitin-proteasome and autophagy pathways. 7–9 VCP plays a role in numerous cellular processes such as cell cycle progression, chromatin remodeling, homotypic membrane fusion (in both the endoplasmic reticulum [ER] and golgi apparatus) and mitochondrial turnover. 10,11 Of those affected with VCP disease, 92% have myopathy, 50% have Paget’s disease of the bone, and 30% have frontotemporal dementia. Although VCP is expressed in almost every cell, its dysfunction in muscle is the most destructive and life shortening. Myogenic tissues either fail to regenerate after injury or degenerate prematurely causing a muscle wasting phenotype. How mutations in VCP lead to poor regeneration/degeneration and the subsequent muscle wasting phenotype is unclear. VCP appears to directly interact with proteins involved in catabolic pathways and thereby affect protein fate. In fact, VCP affects many protein pathways that ultimately influence cell fate and tissue health. The footprint of VCP’s effect on cytokine signaling was first described by Asai et al., 12 when VCP expression was shown to affect nuclear factor kappa-B activity (NFkB, a downstream target of TNFα). In this report, they induced VCP expression and then observed an increase in the activation of NFκB. 12 Clinically, VCP myopathy appears similar to inflammatory- mediated wasting diseases as described in cachexia. Although VCP disease clinically resembles a chronic inflammatory syndrome, there is no inflammatory cell infiltrate and patient plasma shows a normal erythrocyte sedimentation rate (ESR, a global marker of inflammation). It is important to note, however, that ESR is not a 100% sensitive for inflammatory conditions. For example, asthmatic patients can have a waxing and waning chronic inflammation that does not necessarily show an elevated ESR in patient plasma. Because the clinical picture implicating inflammation was so compelling, we decided to investigate the cytokine profile of patient plasma. Our hypothesis is that the dysfunctional protein homeostasis in VCP disease causes a perturbation of cytokine signals that are classically associated with impaired muscle regeneration and muscle wasting. We predict patient plasma will show a cytokine profile enriched for factors associated with muscle cachexia (TNFα and IL-6) and poor in factors that promote muscle regeneration (EGF and IL-4). Methods Clinical evaluation and consenting of patients All subjects were consented and approved for the study in accordance with the institutional review board’s consent procedure Division of Genetics and Metabolism, Department of Pediatrics, University of California, Irvine, California, USA; 2 Institute for Clinical and Translational Science, University of California, Irvine, California, USA; 3 Laboratory of Cellular and Molecular Immunology, University of California Irvine, School of Medicine, Irvine, California, USA. Correspondence: V.E. Kimonis (vkimonis@uci.edu) DOI: 10.1111/cts.12117 WWW.CTSJOURNAL.COM VOLUME 7 • ISSUE 1