Gene-environment interactions in Parkinson's disease

Huntington disease: pathogenesis, biomarkers, and approaches to experimental therapeutics

Huntington disease (HD) is characterized by motor, cognitive and behavioral abnormalities that typically emerge in adulthood in persons who have inherited the mutant gene. HD has a single genetic cause, a well-defined neuropathology, and informative pre-manifest predictive genetic testing. Thus, it has been possible to develop imaging biomarkers of HD progression, not just in the period of manifest illness, but also in the prodromal or "premanifest" period. Striatal atrophy is the most studied, and shows steady progression beginning in the prodromal period beginning up to 15 years before predicted onset, and continuing through the period of manifest illness. Therapeutic targets for HD include the huntingtin protein itself, either by reducing its levels with antisense oligonucleotides or siRNA, or potentially by intervening via posttranslational modifications such as phosphorylation, acetylation, SUMOylation, or proteolytic cleavage. Other strategies involve bolstering the cell's ability to deal with abnormal proteins, either via chaperones or protein degradation machinery. It may be possible to counteract the abnormal transcription caused by mutant huntingtin, with histone deacetylase inhibitors, or to enhance relevant gene products such as Brain Derived Neurotrophic Factor (BDNF). Another tactic is to enhance cellular metabolic defenses, such as with creatine or Coenzyme Q10. Strategies are being devised to use biomarkers, and administer therapeutic agents which can be given safely for long periods of time during the proodromal period, with a goal not just to slow progression, but to delay, or conceivably even prevent, the onset of clinical HD.

Synphilin-1 attenuates neuronal degeneration in the A53T alpha-synuclein transgenic mouse model

Genetic alterations in alpha-synuclein cause autosomal dominant familial Parkinsonism and may contribute to sporadic Parkinson's disease (PD). Synphilin-1 is an alpha-synuclein-interacting protein, with implications in PD pathogenesis related to protein aggregation. Currently, the in vivo role of synphilin-1 in alpha-synuclein-linked pathogenesis is not fully understood. Using the mouse prion protein promoter, we generated synphilin-1 transgenic mice, which did not display PD-like phenotypes. However, synphilin-1/A53T alpha-synuclein double-transgenic mice survived longer than A53T alpha-synuclein single-transgenic mice. There were attenuated A53T alpha-synuclein-induced motor abnormalities and decreased astroglial reaction and neuronal degeneration in brains in double-transgenic mice. Overexpression of synphilin-1 decreased caspase-3 activation, increased beclin-1 and LC3 II expression and promoted formation of aggresome-like structures, suggesting that synphilin-1 alters multiple cellular pathways to protect against neuronal degeneration. These studies demonstrate that synphilin-1 can diminish the severity of alpha-synucleinopathy and play a neuroprotective role against A53T alpha-synuclein toxicity in vivo.

Synphilin-1 exhibits trophic and protective effects against Rotenone toxicity

Synphilin-1 is a cytoplasmic protein with unclear function. Synphilin-1 has been identified as an interaction partner of alpha-synuclein. The interaction between synphilin-1 and alpha-synuclein has implications in Parkinson's disease. In this study, we stably overexpressed human synphilin-1 in mouse N1E-115 neuroblastoma cells. We found that overexpression of synphilin-1 shortened cell growth doubling time and increased neurite outgrowth. Knockdown of endogenous synphilin-1 caused neuronal toxicity and shortened neurite outgrowth. We further found that synphilin-1 increased activation of the extracellular signal-regulated kinases (ERK1/2) and mediated neurite outgrowth. Rotenone, mitochondrial complex I inhibitor, has been shown previously to induce dopaminergic neurodegeneration and Parkinsonism in rats and Drosophila. We found that Rotenone induced apoptotic cell death in N1E-115 cells via caspase-3 activation and poly (ADP-ribose) polymerase (PARP) cleavage. Overexpression of synphilin-1 significantly reduced Rotenone-induced cell death, caspase-3 activation and PARP cleavage. The results indicate that synphilin-1 displays trophic and protective effects in vitro, suggesting that synphilin-1 may play a protective role in Parkinson's disease (PD) pathogenesis and may lead to a potential therapeutic target for PD intervention.

Animal models of gene-environment interactions in schizophrenia

The pathogenesis of schizophrenia and related mental illnesses likely involves multiple interactions between susceptibility genes of small effects and environmental factors. Gene-environment interactions occur across different stages of neurodevelopment to produce heterogeneous clinical and pathological manifestations of the disease. The main obstacle for mechanistic studies of gene-environment interplay has been the paucity of appropriate experimental systems for elucidating the molecular pathways that mediate gene-environment interactions relevant to schizophrenia. Recent advances in psychiatric genetics and a plethora of experimental data from animal studies allow us to suggest a new approach to gene-environment interactions in schizophrenia. We propose that animal models based on identified genetic mutations and measurable environment factors will help advance studies of the molecular mechanisms of gene-environment interplay.