Models of dystonia: an update

Although dystonia represents the third most common movement disorder, its pathophysiology remains still poorly understood. In the past two decades, multiple models have been generated, improving our knowledge on the molecular and cellular bases of this heterogeneous group of movement disorders. In this short survey, we will focus on recently generated novel models of DYT1 dystonia, the most common form of genetic, "isolated" dystonia. These models clearly indicate the existence of multiple signaling pathways affected by the protein mutation causative of DYT1 dystonia, torsinA, paving the way for potentially multiple, novel targets for pharmacological intervention.

Abnormal striatal plasticity in a DYT11/SGCE myoclonus dystonia mouse model is reversed by adenosine A2A receptor inhibition

Striatal dysfunction is implicated in many movement disorders. However, the precise nature of defects often remains uncharacterized, which hinders therapy development. Here we examined striatal function in a mouse model of the incurable movement disorder, myoclonus dystonia, caused by SGCE mutations. Using RNAseq we found surprisingly normal gene expression, including normal levels of neuronal subclass markers to strongly suggest that striatal microcircuitry is spared by the disease insult. We then functionally characterized Sgce mutant medium spiny projection neurons (MSNs) and cholinergic interneurons (ChIs). This revealed normal intrinsic electrophysiological properties and normal responses to basic excitatory and inhibitory neurotransmission. Nevertheless, high-frequency stimulation in Sgce mutants failed to induce normal long-term depression (LTD) at corticostriatal glutamatergic synapses. We also found that pharmacological manipulation of MSNs by inhibiting adenosine 2A receptors (A_2AR) restores LTD, again pointing to structurally intact striatal circuitry. The fact that Sgce loss specifically inhibits LTD implicates this neurophysiological defect in myoclonus dystonia, and emphasizes that neurophysiological changes can occur in the absence of broad striatal dysfunction. Further, the positive effect of A_2AR antagonists indicates that this drug class be tested in DYT11/SGCE dystonia.

[Epigenetics and environmental exposure to xenobiotics]

Environmental pollution, together with predisposing genetic factors, plays a key role in determining short and long-term adverse effects on human health. In the industrialized countries the identification of etiology related to diseases of environmental origin has then become a research of priority interest. With regard to this, it has been widely demonstrated that different chemical compounds, such as endocrine disruptors, are able to modify the epigenetic characteristics of a human being. According to recent studies, the paradigm "genotype is strongly correlated with a phenotype" is changing in favor of the concept that a phenotype is defined by a "genotype and by an epigenome". Thus, there is a genotype identical for all cells associated to the epigenome that causes changes in gene expression without modifying the nucleotide sequence of the genome, through alterations in DNA methylation, histone modifications and the pathway of small non-coding RNAs. The epigenome is easily affected by different factors, such as aberrations of normal epigenetic processes that can be caused by environmental factors as exposure to xenobiotics, social behavior and nutritional deficiencies. Epigenetic changes are thus a biological response to environmental stress factors and may be transmitted to the offspring. As the elimination of the environmental factor determines the possible reversion of epigenetic modifications, it seems not to play a role in the natural selection process. However, epigenetic aberrations affect gene expression by interfering with the stability and survival of cells and with the inactivation of onco-suppressor genes. Thus, it is of considerable interest to investigate about the possible elements of induction of epigenetic processes in order to implement prevention protocols. Moreover, the gene expression screening through high through-put techniques like microarray, represent a new tool for the identification of new epigenetic indicators in order to monitor the early biological effects on the population exposed to xenobiotics.