Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
General Comments Golden Age of neuroscience has also been translated to RLS research Fe is central to brain function and RLS etiology Vast complexity = vast opportunity More answers = more questions Expect surprises Take home message: RLS is most likely associated with decreased brain Fe levels. There is an alteration in Fe transport, metabolism and storage proteins. But should you just focus on Fe? Yes and no Not exhaustive, but what’s known Decreased transferrin receptor expression in RLS (Connor et al., Neurology 62:1563-7, 2004). Ferritin subunits in CSF are decreased in RLS (Clardy et al., J Lab Clin Invest 147:167-173). “At this time, it cannot be determined if the lower levels of pro-hepcidin in the CSF represent a compensatory response to the decreased levels of iron in the brain or a defective signaling mechanism in RLS” (Clardy et al., J Neurol Sci 247:173-179, 2006). CSF ferritin poorly correlates with serum ferritin in RLS (Earley et al., Sleep 28:1069-1075, 2005). Iron uptake occurs via the transferrin receptor and DMT1. Steap3 is a ferrireductase. Ferroportin is the only known cellular iron exporter, and ceruloplasmin is a ferroxidase mediating efficient cellular iron release. Iron homeostasis is regulated by hepcidin, a circulating peptide that binds to ferroportin, mediating uptake and degradation of this exporter. Iron enters mitochondria via mitoferrin, and frataxin is a mitochondrial protein mediating Fe-S cluster formation and heme biosynthesis. The human DMT1 gene, maps to chromosome 12q near the RLS1 locus (Xiong et al., Neurology 144, 911-917, 2007). Samples from RLS families with compatible linkage to the RLS1 locus on 12q were sequenced in both the coding regions and the long stretches of UTR sequences. No detectable difference in DMT1 protein levels between RLS patient lymphoblastoid cell lines and controls. Linkage analyses failed to identify any significant linkage signals within the DMT1 gene region. Sequencing did not detect any sequence variant(s) compatible with DMT1 harboring RLS causative mutation(s). No association between ten SNPs, spanning the whole DMT1 gene region, and RLS status. Sequence analysis and association between SNPs in Fe associated genes and RLS Iron uptake occurs via the transferrin receptor and DMT1. Steap3 is a ferrireductase. Ferroportin is the only known cellular iron exporter, and ceruloplasmin is a ferroxidase mediating efficient cellular iron release. Iron homeostasis is regulated by hepcidin, a circulating peptide that binds to ferroportin, mediating uptake and degradation of this exporter. Iron enters mitochondria via mitoferrin, and frataxin is a mitochondrial protein mediating Fe-S cluster formation and heme biosynthesis. Mn MRI and AAS correlations R1 vs. [Mn] for CN and MnT 1.1 Cerebellum Brainstem 1 Midbrain Hippocampus R1 (1/s) 0.9 Striatum Cortex 0.8 0.7 0.6 0.5 0 0.05 0.1 0.15 0.2 0.25 [Mn] (mmol/kg tissue) 0.3 0.35 MRI findings - limitations R1 was strongly correlated with tissue Mn levels. However, the slopes of the linear regression fits varied significantly among different brain regions A simple linear model failed to explain the changes in relaxation rate when both Mn and Fe brain contents changed. When Mn and Fe are both changing, their combined influence on MRI signals is complicated. In such case, the simple linear model is not suitable to explain the change of MRI relaxation rates Other metals may contribute to the R1s, R2s. ID is associated with increased brain copper levels Garcia et al., Toxicol Sci 95:205-14, 2007 Complimentary Experimental Models Surdej P, Richman L, Kühn LC. Differential translational regulation of IRE-containing mRNAs in Drosophila melanogaster by endogenous IRP and a constitutive human IRP1 mutant. Insect Biochem Mol Biol 38:891-4, 2008. Missirlis F, Kosmidis S, Brody T, Mavrakis M, Holmberg S, Odenwald WF, Skoulakis EM, Rouault TA. Homeostatic mechanisms for iron storage revealed by genetic manipulations and live imaging of Drosophila ferritin. Genetics 177:89-100, 2007. Bagheri N, Stelling J, Doyle FJ 3rd. Circadian phase resetting via single and multiple control targets. PLoS Comput Biol. 4;4 2008. Power of genetics (screen for suppressor, complementation, forward and reverse genetics) combined with availability of multiple knockout or loss-of-function mutation GFP expressing strains, as well as behavioral tests Role of DMT-1 in Mn-induced death in C. elegans Mn Concentrations in Smf mutants smf-3 expression pattern by transcriptional and translational GFP fusions E) smf-3::GFP expression in the intestine. F) smf-3::GFP expression in the epidermis hyp7. G) smf-3::GFP expression in the epidermis hyp1 to hyp6. Working model of Mn transport in the worm SMF-1 and SMF-3 are the DMT1 isoforms responsible for Mn uptake. SMF-2 is involved in Mn sensing and uptake regulation via inhibition of pharyngeal pumping. Schematic model of a C. elegans DA neuron containing known and predicted genes involved in DA biosynthesis and metabolism TH, tyrosine hydroxylase; GTPCH, GTP cyclohydrolase; AAAD, aromatic L-amino acid decarboxylase; MAO, monoamine oxidase; VMAT, vesicular monoamine transporter; DAT-1, dopamine transporter; CeDOP1, D1-like DA receptor; CeDOP2, D2-like DA receptor; COMT, cacholO-methyltransferase. CeDOP2 CeDOP2 Genetic mutants are indicated in italics. Selective Sensitivity of C. elegans to Mn Future Objectives Identify the neuropathological mechanisms of RLS? Focus on Fe, but not all the keys may be under the streetlight. Studies in animals exposed to precipitants of RLS, e.g., Fe depletion. How can complimentary models be utilized for better understanding of the pathophysiology? Are their promising models that can be used, and what is the best strategy for utilizing these models to assess the genetic predisposition and environmental influences (gene x environment interactions?) Interactions with other metals. studies to determine how dopamine pathways are altered in RLS and relationships to circadian rhythms. Future Objectives Brain bank of deceased RLS patients? Sequence analysis and association between SNPs in Fe (metals?) associated genes and RLS. Family studies to distinguish genetic and non-genetic forms and to map, identify, and characterize genes involved in the etiology of RLS. Clinical trials are needed to study the efficacy of iron supplementation in RLS. Develop surrogate measures of Fe status Transferrin synthesis is not specific to Fe availability as it is decreased during inflammation and other conditions. The serum soluble transferrin receptor, a truncated form of the membrane receptor produced by enzymatic cleavage is a direct reflection of cellular transferrin receptors, showing little variability. The hereditary disorders of brain iron metabolism Aceruloplasminemia Neuroferritinopathy Genetics Autosomal recessive loss-offunction mutations ceruloplasmin gene Autosomal dominant (dominantnegative) mutations ferritin light chain gene Presentation Third decade—diabetes Third through sixth decade Fifth decade—neurologic Defect Brain iron recycling Brain iron storage Pathogenesis Brain iron accumulation Brain iron accumulation Systemic iron accumulation Clinical Diabetes, anemia, dementia Dementia, dystonia, dysarthria Dystonia, dysarthria Pathology Iron accumulation in astrocytes Iron accumulation in astrocytes Neuronal loss Neuronal loss