Huntington's disease. Exploiting expression

Histone deacetylases inhibitors (HDACis) as novel therapeutic application in various clinical diseases

Accumulating evidence suggests that histone hypoacetylation which is partly mediated by histone deacetylase (HDAC), plays a causative role in the etiology of various clinical disorders such as cancer and central nervous diseases. HDAC inhibitors (HDACis) are natural or synthetic small molecules that can inhibit the activities of HDACs and restore or increase the level of histone acetylation, thus may represent the potential approach to treating a number of clinical disorders. This manuscript reviewed the progress of the most recent experimental application of HDACis as novel potential drugs or agents in a large number of clinical disorders including various brain disorders including neurodegenerative and neurodevelopmental cognitive disorders and psychiatric diseases like depression, anxiety, fear and schizophrenia, and cancer, endometriosis and cell reprogramming in somatic cell nuclear transfer in human and animal models of disease, and concluded that HDACis as potential novel therapeutic agents could be used alone or in adjunct to other pharmacological agents in various clinical diseases.

Effect of different exercise protocols on histone acetyltransferases and histone deacetylases activities in rat hippocampus

Regular and moderate exercise has been considered an interesting neuroprotective strategy. Although the mechanisms by which physical exercise alters brain function are not clear, it appears that neuroprotective properties of exercise could be related to chromatin remodeling, specifically the induction of histone acetylation through modulation of histone deacetylases (HDAC) and histone acetyltransferases (HAT) activities. The aim of the present work was to investigate the effect of exercise on HDAC and HAT activities in rat whole hippocampus at different times after treadmill. Adult male Wistar rats were assigned to non-exercised (sedentary) and exercised groups on different protocols: a single session of treadmill exercise (running for 20 min) and a chronic treadmill protocol (running once daily for 20 min, for 2 weeks). The effects of exercise on HDAC and HAT activities were measured immediately, 1 h and 18 h after the single session or the last training session of chronic treadmill exercise using specific assay kits. The single session of treadmill exercise reduced HDAC activity, increased HAT activity and increased the HAT/HDAC balance in rat hippocampus immediately and 1 h after exercise, an indicative of histone hyperacetylation status. The acetylation balance was also influenced by the circadian rhythm, since the HAT/HDAC ratio was significantly decreased in the early morning in all groups when compared to the afternoon. These data support the hypothesis that exercise neuroprotective effects may be related, at least in part, to acetylation levels through modulation of HAT and HDAC activities. We also demonstrated circadian changes in the HAT and HDAC activities and, consequently, in the acetylation levels.

Deregulation of HDAC1 by p25/Cdk5 in neurotoxicity

Aberrant cell-cycle activity and DNA damage are emerging as important pathological components in various neurodegenerative conditions. However, their underlying mechanisms are poorly understood. Here, we show that deregulation of histone deacetylase 1 (HDAC1) activity by p25/Cdk5 induces aberrant cell-cycle activity and double-strand DNA breaks leading to neurotoxicity. In a transgenic model for neurodegeneration, p25/Cdk5 activity elicited cell-cycle activity and double-strand DNA breaks that preceded neuronal death. Inhibition of HDAC1 activity by p25/Cdk5 was identified as an underlying mechanism for these events, and HDAC1 gain of function provided potent protection against DNA damage and neurotoxicity in cultured neurons and an in vivo model for ischemia. Our findings outline a pathological signaling pathway illustrating the importance of maintaining HDAC1 activity in the adult neuron. This pathway constitutes a molecular link between aberrant cell-cycle activity and DNA damage and is a potential target for therapeutics against diseases and conditions involving neuronal death.

Epigenetic targets of HDAC inhibition in neurodegenerative and psychiatric disorders

Epigenetic chromatin remodeling and modifications of DNA represent central mechanisms for regulation of gene expression during brain development and in memory formation. Emerging evidence implicates epigenetic modifications in disorders of synaptic plasticity and cognition. This review focuses on recent findings that HDAC inhibitors can ameliorate deficits in synaptic plasticity, cognition, and stress-related behaviors in a wide range of neurologic and psychiatric disorders including Huntington's disease, Parkinson's disease, anxiety and mood disorders, Rubinstein-Taybi syndrome, and Rett syndrome. These agents may prove useful in the clinic for the treatment of the cognitive impairments that are central elements of many neurodevelopmental, neurological, and psychiatric disorders.

Proteomics in neurosciences

This review provides an outline of the most important proteomic applications in the study of neurodegenerative disorders including Alzheimer's (AD), Parkinson's (PD), Huntington's (HD), and prion diseases, and also discusses advances in cancer and addiction. One of the scopes is to illustrate the potential of proteomics in the biomarkers discovery of these diseases. Finally, this article comments the advantages and drawbacks of the most commonly used techniques and methods for samples preparation.

Mitochondrial-dependent Ca2+ handling in Huntington's disease striatal cells: effect of histone deacetylase inhibitors

Evidence suggests that neuronal dysfunction in Huntington's disease (HD) striatum involves deficits in mitochondrial function and in Ca2+ handling. However, the relationship between mitochondria and Ca2+ handling has been incompletely studied in intact HD striatal cells. Treatment with histone deacetylase (HDAC) inhibitors reduces cell death in HD models, but the effects of this promising therapy on cellular function are mostly unknown. Here, we use real-time functional imaging of intracellular Ca2+ and mitochondrial membrane potential to explore the role of in situ HD mitochondria in Ca2+ handling. Immortalized striatal (STHdh) cells and striatal neurons from transgenic mice, expressing full-length mutant huntingtin (Htt), were used to model HD. We show that (1) active glycolysis in STHdh cells occludes the mitochondrial role in Ca2+ handling as well as the effects of mitochondrial inhibitors, (2) STHdh cells and striatal neurons in the absence of glycolysis are critically dependent on oxidative phosphorylation for energy-dependent Ca2+ handling, (3) expression of full-length mutant Htt is associated with deficits in mitochondrial-dependent Ca2+ handling that can be ameliorated by treatment with HDAC inhibitors (treatment with trichostatin A or sodium butyrate decreases the proportion of STHdh cells losing Ca2+ homeostasis after Ca2+-ionophore challenging, and accelerates the restoration of intracellular Ca2+ in striatal neurons challenged with NMDA), and (4) neurons with different response patterns to NMDA receptor activation exhibit different average somatic areas and are differentially affected by treatment with HDAC inhibitors, suggesting subpopulation or functional state specificity. These findings indicate that neuroprotection induced by HDAC inhibitors involves more efficient Ca2+ handling, thus improving the neuronal ability to cope with excitotoxic stimuli.

Interaction of the nuclear matrix protein NAKAP with HypA and huntingtin: implications for nuclear toxicity in Huntington's disease pathogenesis

Although expansion of a polyglutamine tract in the huntingtin protein is known to cause Huntington's disease (HD), there is considerable debate as to how this mutation leads to the selective neuronal loss that characterizes the disease. The observation that mutant huntingtin accumulates in neuronal nuclei has led to the hypothesis that the molecular mechanism may involve the disruption of specific nuclear activities. Recently, several nuclear interaction partners for huntingtin have been identified, including HypA, a splicing factor-like protein of unknown function. Using a yeast two-hybrid screen, we have identified the interaction of HypA with the nuclear scaffold protein NAKAP. Interaction of NAKAP with HypA is specific and occurs both in yeast and in vitro. Deletion-mapping studies indicate that binding occurs via a proline-rich domain in NAKAP with a WW domain of HypA. In cultured cells, NAKAP and HypA localize within the nucleus and copurify with the nuclear matrix. Furthermore, NAKAP associates with HypA from human brain and copurifies with huntingtin protein in brain tissue obtained from HD patients. In HD neurons, NAKAP and mutant huntingtin were colocalized to the nuclear matrix and were found to be components of nuclear aggregates. Hence, the NAKAP-HypA scaffold is a potential nuclear docking site for huntingtin protein and may contribute to the nuclear accumulation of huntingtin observed in HD.

Limited proteolysis differentially modulates the stability and subcellular localization of domains of RPGRIP1 that are distinctly affected by mutations in Leber's congenital amaurosis

The retinitis pigmentosa GTPase regulator (RPGR) protein interacts with the retinitis pigmentosa GTPase regulator interacting protein-1 (RPGRIP1). Genetic lesions in the cognate genes lead to distinct and severe human retinal dystrophies. The biological role of these proteins in retinal function and pathogenesis of retinal diseases is elusive. Here, we present the first physiological assay of the role of RPGRIP1 and mutations therein. We found that the monoallelic and homozygous mutations, DeltaE1279 and D1114G, in the RPGR-interacting domain (RID) of RPGRIP1, enhance and abolish, respectively, its interaction in vivo with RPGR without affecting the stability of RID. In contrast to RID(WT) and RID(D1114G), chemical genetics shows that the interaction of RID(DeltaE1279) with RPGR is resistant to various stress treatments such as osmotic, pH and heat-shock stimuli. Hence, RID(D1114G) and RID(DeltaE1279) constitute loss- and gain-of-function mutations. Moreover, we find that the isoforms, bRPGRIP1 and bRPGRIP1b, undergo limited proteolysis constitutively in vivo in the cytoplasm compartment. This leads to the relocation and accumulation of a small and stable N-terminal domain of approximately 7 kDa to the nucleus, whereas the cytosolic C-terminal domain of RPGRIP1 is degraded and short-lived. The RID(D1114G) and RID(DeltaE1279) mutations exhibit strong cis-acting and antagonistic biological effects on the nuclear relocation, subcellular distribution and proteolytic cleavage of RPGRIP1 and/or domains thereof. These data support distinct and spatiotemporal subcellular-specific roles to RPGRIP1. A novel RPGRIP1-mediated nucleocytoplasmic crosstalk and transport pathway regulated by RID, and hence by RPGR, emerges with implications in the molecular pathogenesis of retinopathies, and a model to other diseases.

Reactivation of silenced genes and transcriptional therapy

The purpose of this review is to discuss the potential role of "transcriptional therapy" to modulate the expression of target genes in order to treat monogenic as well as multifactorial disorders. In vitro and in vivo experiments with DNA demethylating and histone hyperacetylating drugs are currently performed in several laboratories on a variety of genes. In attempting to place these results into perspective, we divided the target genes into four major categories: (1) single genes with a hypermethylated CpG island; (2) single genes without a CpG island; (3) groups of genes silenced by aberrant DNA methylation; and (4) groups of genes silenced by lack of histone acetylation. We discuss the latest advances in the field of chromatin regulation and, in particular, the role of histone methylation and that of RNA interference in gene silencing. We can expect that in the future regulation of transcription will become an effective treatment for several genetic conditions.