ABSTRACT
Inflammation is a growing area of research in neurodegeneration. In Huntington's disease (HD), a fatal inherited neurodegenerative disease caused by a CAG-repeat expansion in the gene encoding huntingtin, patients have increased plasma levels of inflammatory cytokines and circulating monocytes that are hyper-responsive to immune stimuli. Several mouse models of HD also show elevated plasma levels of inflammatory cytokines. To further determine the degree to which these models recapitulate observations in HD patients, we evaluated various myeloid cell populations from different HD mouse models to determine whether they are similarly hyper-responsive, as well as measuring other aspects of myeloid cell function. Myeloid cells from each of the three mouse models studied, R6/2, HdhQ150 knock-in and YAC128, showed increased cytokine production when stimulated. However, bone marrow CD11b(+) cells did not show the same hyper-responsive phenotype as spleen and blood cells. Furthermore, macrophages isolated from R6/2 mice show increased levels of phagocytosis, similar to findings in HD patients. Taken together, these results show significant promise for these mouse models to be used to study targeting innate immune pathways identified in human cells, thereby helping to understand the role the peripheral immune system plays in HD progression.
Subject(s)
Cytokines/immunology , Disease Models, Animal , Huntington Disease/immunology , Immunity, Innate/immunology , Inflammation/immunology , Myeloid Cells/immunology , Animals , Female , Male , Mice , Mice, Inbred C57BLABSTRACT
BACKGROUND: In addition to classical neurological symptoms, Huntington's disease (HD) is complicated by peripheral pathology, including progressive skeletal muscle wasting, and common skeletal muscle gene expression changes have been shown in HD mice and human HD. OBJECTIVE: To highlight possible mechanisms underlying muscle wasting in HD, we examined gene expression in pathways governing skeletal muscle contractility, skeletal myogenesis, skeletal muscle wasting, apoptosis and the NFκB signaling pathway in two HD mouse models (the transgenic R6/2 and full-length knock-in Q175). In addition, we assessed circulating markers that increase in response to skeletal muscle injury, skeletal Troponin I (sTnI), fatty acid binding protein 3 (FABP3), and Myosin light chain 3 (Myl3). METHODS: We measured gene expression in muscle tissue as well as in cultured primary myocytes using qPCR. Concentrations of cytokines and muscle proteins were obtained using multiplex ELISA. RESULTS: Circulating markers of muscle injury (sTnI, FABP3, and Myl3) were significantly increased in mouse serum. In skeletal muscle, we observed reduced gene expression of components involved in muscle contractility, with pronounced downregulation of Acta1, Myh2 and Tnni2, among others. Alongside, we found increased expression of caspases (3 and 8) and key elements of the NFκB signaling pathway, p65/RelA, Tradd, and TRAF5. We also found similar gene expression alterations in cultured primary myocytes from R6/2 mice stimulated with TNF-α. CONCLUSIONS: Our results indicate that activation of apoptotic and NFκB pathways occur alongside down-regulation of key compartments of the muscle contractility unit in skeletal muscle of HD mice, and muscle atrophy could possibly be a source of circulating disease progression markers.
Subject(s)
Huntington Disease/genetics , Muscle, Skeletal/metabolism , Muscular Atrophy/genetics , Animals , Biomarkers/metabolism , Caspase 3/genetics , Caspase 3/metabolism , Caspase 8/genetics , Caspase 8/metabolism , Disease Models, Animal , Down-Regulation , Fatty Acid Binding Protein 3 , Fatty Acid-Binding Proteins/genetics , Fatty Acid-Binding Proteins/metabolism , Huntington Disease/complications , Huntington Disease/metabolism , Mice , Mice, Transgenic , Muscle Contraction/genetics , Muscular Atrophy/etiology , Muscular Atrophy/metabolism , Myosin Heavy Chains/genetics , Myosin Heavy Chains/metabolism , Myosin Light Chains/genetics , Myosin Light Chains/metabolism , NF-kappa B/genetics , NF-kappa B/metabolism , Signal Transduction , TNF Receptor-Associated Death Domain Protein/genetics , TNF Receptor-Associated Death Domain Protein/metabolism , TNF Receptor-Associated Factor 5/genetics , TNF Receptor-Associated Factor 5/metabolism , Transcription Factor RelA/genetics , Transcription Factor RelA/metabolism , Transcriptome , Troponin I/genetics , Troponin I/metabolismABSTRACT
Huntington's disease is an inherited neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin gene. The peripheral innate immune system contributes to Huntington's disease pathogenesis and has been targeted successfully to modulate disease progression, but mechanistic understanding relating this to mutant huntingtin expression in immune cells has been lacking. Here we demonstrate that human Huntington's disease myeloid cells produce excessive inflammatory cytokines as a result of the cell-intrinsic effects of mutant huntingtin expression. A direct effect of mutant huntingtin on the NFκB pathway, whereby it interacts with IKKγ, leads to increased degradation of IκB and subsequent nuclear translocation of RelA. Transcriptional alterations in intracellular immune signalling pathways are also observed. Using a novel method of small interfering RNA delivery to lower huntingtin expression, we show reversal of disease-associated alterations in cellular function-the first time this has been demonstrated in primary human cells. Glucan-encapsulated small interfering RNA particles were used to lower huntingtin levels in human Huntington's disease monocytes/macrophages, resulting in a reversal of huntingtin-induced elevated cytokine production and transcriptional changes. These findings improve our understanding of the role of innate immunity in neurodegeneration, introduce glucan-encapsulated small interfering RNA particles as tool for studying cellular pathogenesis ex vivo in human cells and raise the prospect of immune cell-directed HTT-lowering as a therapeutic in Huntington's disease.
Subject(s)
Huntington Disease/genetics , Huntington Disease/pathology , Myeloid Cells/pathology , NF-kappa B/antagonists & inhibitors , NF-kappa B/physiology , Nerve Tissue Proteins/antagonists & inhibitors , Signal Transduction/genetics , Gene Expression Regulation/immunology , Humans , Huntingtin Protein , Huntington Disease/metabolism , Immunity, Innate/genetics , Myeloid Cells/immunology , Nerve Tissue Proteins/biosynthesis , Nerve Tissue Proteins/genetics , RNA, Small Interfering/therapeutic use , Signal Transduction/immunology , U937 CellsABSTRACT
BACKGROUND: Huntington's Disease (HD) is a hereditary, progressive neurodegenerative disorder characterised by both neurological and systemic symptoms. In HD, immune changes can be observed before the onset of overt clinical features raising the possibility that inflammatory markers in plasma could be used to track disease progression. It has previously been demonstrated that a widespread, progressive innate immune response is detectable in plasma throughout the course of HD. OBJECTIVE: The aim of the present study was to investigate the potential of several components of inflammation and innate immunity as plasma biomarkers in HD. METHODS: We utilised antibody-based detection technologies as well as mass spectrometric quantification, multiple reaction monitoring (MRM-MS). RESULTS: Levels of several markers previously described as altered in HD, such as clusterin, complement component 4, complement component 9 and α-2 macroglobulin did not differ between healthy controls and HD subjects as measured by Luminex, ELISA or MRM-MS. C-reactive protein was decreased in early HD, while the other immune markers tested were unaltered. CONCLUSIONS: Although only C-reactive protein was found to be reduced in early HD, some of the inflammatory markers measured correlated with clinical measures.
