Tõnis Timmusk

Bio: Tõnis Timmusk is an academic researcher from Tallinn University of Technology. The author has contributed to research in topics: Neurotrophic factors & Brain-derived neurotrophic factor. The author has an hindex of 41, co-authored 105 publications receiving 11056 citations. Previous affiliations of Tõnis Timmusk include Karolinska Institutet & Uppsala University.

Loss of Huntingtin-Mediated BDNF Gene Transcription in Huntington's Disease

Abstract: Huntingtin is a 350-kilodalton protein of unknown function that is mutated in Huntington's disease (HD), a neurodegenerative disorder. The mutant protein is presumed to acquire a toxic gain of function that is detrimental to striatal neurons in the brain. However, loss of a beneficial activity of wild-type huntingtin may also cause the death of striatal neurons. Here we demonstrate that wild-type huntingtin up-regulates transcription of brain-derived neurotrophic factor (BDNF), a pro-survival factor produced by cortical neurons that is necessary for survival of striatal neurons in the brain. We show that this beneficial activity of huntingtin is lost when the protein becomes mutated, resulting in decreased production of cortical BDNF. This leads to insufficient neurotrophic support for striatal neurons, which then die. Restoring wild-type huntingtin activity and increasing BDNF production may be therapeutic approaches for treating HD.

Mouse and rat BDNF gene structure and expression revisited

Abstract: Brain-derived neurotrophic factor (BDNF) has important functions in the development of the nervous system and in brain plasticity-related processes such as memory, learning, and drug addiction. Despite the fact that the function and regulation of rodent BDNF gene expression have received close attention during the last decade, knowledge of the structural organization of mouse and rat BDNF gene has remained incomplete. We have identified and characterized several mouse and rat BDNF transcripts containing novel 5′ untranslated exons and introduced a new numbering system for mouse and rat BDNF exons. According to our results both mouse and rat BDNF gene consist of eight 5′ untranslated exons and one protein coding 3′ exon. Transcription of the gene results in BDNF transcripts containing one of the eight 5′ exons spliced to the protein coding exon and in a transcript containing only 5′ extended protein coding exon. We also report the distinct tissue-specific expression profiles of each of the mouse and rat 5′ exon-specific transcripts in different brain regions and nonneural tissues. In addition, we show that kainic acid-induced seizures that lead to changes in cellular Ca2+ levels as well as inhibition of DNA methylation and histone deacetylation contribute to the differential regulation of the expression of BDNF transcripts. Finally, we confirm that mouse and rat BDNF gene loci do not encode antisense mRNA transcripts, suggesting that mechanisms of regulation for rodent and human BDNF genes differ substantially. © 2006 Wiley-Liss, Inc.

Huntingtin interacts with REST/NRSF to modulate the transcription of NRSE-controlled neuronal genes.

Abstract: Huntingtin protein is mutated in Huntington disease. We previously reported that wild-type but not mutant huntingtin stimulates transcription of the gene encoding brain-derived neurotrophic factor (BDNF; ref. 2). Here we show that the neuron restrictive silencer element (NRSE) is the target of wild-type huntingtin activity on BDNF promoter II. Wild-type huntingtin inhibits the silencing activity of NRSE, increasing transcription of BDNF. We show that this effect occurs through cytoplasmic sequestering of repressor element-1 transcription factor/neuron restrictive silencer factor (REST/NRSF), the transcription factor that binds to NRSE. In contrast, aberrant accumulation of REST/NRSF in the nucleus is present in Huntington disease. We show that wild-type huntingtin coimmunoprecipitates with REST/NRSF and that less immunoprecipitated material is found in brain tissue with Huntington disease. We also report that wild-type huntingtin acts as a positive transcriptional regulator for other NRSE-containing genes involved in the maintenance of the neuronal phenotype. Consistently, loss of expression of NRSE-controlled neuronal genes is shown in cells, mice and human brain with Huntington disease. We conclude that wild-type huntingtin acts in the cytoplasm of neurons to regulate the availability of REST/NRSF to its nuclear NRSE-binding site and that this control is lost in the pathology of Huntington disease. These data identify a new mechanism by which mutation of huntingtin causes loss of transcription of neuronal genes.

Differential expression of mRNAs for neurotrophins and their receptors after axotomy of the sciatic nerve

Abstract: The neurotrophin family includes NGF, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4). Previous studies have demonstrated that expression of NGF and its low-affinity receptor is induced in nonneuronal cells of the distal segment of the transected sciatic nerve suggesting a role for NGF during axonal regeneration (Johnson, E. M., M. Taniuchi, and P. S. DeStefano. 1988. Trends Neurosci. 11:299-304). To assess the role of the other neurotrophins and the members of the family of Trk signaling neurotrophin receptors, we have here quantified the levels of mRNAs for BDNF, NT-3, and NT-4 as well as mRNAs for trkA, trkB, and trkC at different times after transection of the sciatic nerve in adult rats. A marked increase of BDNF and NT-4 mRNAs in the distal segment of the sciatic nerve was seen 2 wk after the lesion. The increase in BDNF mRNA was mediated by a selective activation of the BDNF exon IV promoter and adrenalectomy attenuated this increase by 50%. NT-3 mRNA, on the other hand, decreased shortly after the transection but returned to control levels 2 wk later. In Schwann cells ensheathing the sciatic nerve, only trkB mRNA encoding truncated TrkB receptors was detected with reduced levels in the distal part of the lesioned nerve. Similar results were seen using a probe that detects all forms of trkC mRNA. In the denervated gastrocnemius muscle, the level of BDNF mRNA increased, NT-3 mRNA did not change, while NT-4 mRNA decreased. In the spinal cord, only small changes were seen in the levels of neutrophin and trk mRNAs. These results show that expression of mRNAs for neurotrophins and their Trk receptors is differentially regulated after a peripheral nerve injury. Based on these results a model is presented for how the different neurotrophins could cooperate to promote regeneration of injured peripheral nerves.

Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study

Abstract: Summary Background Since December, 2019, Wuhan, China, has experienced an outbreak of coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Epidemiological and clinical characteristics of patients with COVID-19 have been reported but risk factors for mortality and a detailed clinical course of illness, including viral shedding, have not been well described. Methods In this retrospective, multicentre cohort study, we included all adult inpatients (≥18 years old) with laboratory-confirmed COVID-19 from Jinyintan Hospital and Wuhan Pulmonary Hospital (Wuhan, China) who had been discharged or had died by Jan 31, 2020. Demographic, clinical, treatment, and laboratory data, including serial samples for viral RNA detection, were extracted from electronic medical records and compared between survivors and non-survivors. We used univariable and multivariable logistic regression methods to explore the risk factors associated with in-hospital death. Findings 191 patients (135 from Jinyintan Hospital and 56 from Wuhan Pulmonary Hospital) were included in this study, of whom 137 were discharged and 54 died in hospital. 91 (48%) patients had a comorbidity, with hypertension being the most common (58 [30%] patients), followed by diabetes (36 [19%] patients) and coronary heart disease (15 [8%] patients). Multivariable regression showed increasing odds of in-hospital death associated with older age (odds ratio 1·10, 95% CI 1·03–1·17, per year increase; p=0·0043), higher Sequential Organ Failure Assessment (SOFA) score (5·65, 2·61–12·23; p Interpretation The potential risk factors of older age, high SOFA score, and d-dimer greater than 1 μg/mL could help clinicians to identify patients with poor prognosis at an early stage. Prolonged viral shedding provides the rationale for a strategy of isolation of infected patients and optimal antiviral interventions in the future. Funding Chinese Academy of Medical Sciences Innovation Fund for Medical Sciences; National Science Grant for Distinguished Young Scholars; National Key Research and Development Program of China; The Beijing Science and Technology Project; and Major Projects of National Science and Technology on New Drug Creation and Development.

Association analyses of 249,796 individuals reveal 18 new loci associated with body mass index

Abstract: Obesity is globally prevalent and highly heritable, but its underlying genetic factors remain largely elusive. To identify genetic loci for obesity susceptibility, we examined associations between body mass index and similar to 2.8 million SNPs in up to 123,865 individuals with targeted follow up of 42 SNPs in up to 125,931 additional individuals. We confirmed 14 known obesity susceptibility loci and identified 18 new loci associated with body mass index (P < 5 x 10(-8)), one of which includes a copy number variant near GPRC5B. Some loci (at MC4R, POMC, SH2B1 and BDNF) map near key hypothalamic regulators of energy balance, and one of these loci is near GIPR, an incretin receptor. Furthermore, genes in other newly associated loci may provide new insights into human body weight regulation.

Integrative Genomics Viewer

Abstract: Rapid improvements in sequencing and array-based platforms are resulting in a flood of diverse genome-wide data, including data from exome and whole-genome sequencing, epigenetic surveys, expression profiling of coding and noncoding RNAs, single nucleotide polymorphism (SNP) and copy number profiling, and functional assays. Analysis of these large, diverse data sets holds the promise of a more comprehensive understanding of the genome and its relation to human disease. Experienced and knowledgeable human review is an essential component of this process, complementing computational approaches. This calls for efficient and intuitive visualization tools able to scale to very large data sets and to flexibly integrate multiple data types, including clinical data. However, the sheer volume and scope of data pose a significant challenge to the development of such tools.

Regulation of BDNF and trkB mRNA in Rat Brain by Chronic Electroconvulsive Seizure and Antidepressant Drug Treatments

Abstract: The influence of chronic electroconvulsive seizure (ECS) or antidepressant drug treatments on expression of brain-derived neurotrophic factor (BDNF) and its receptor, trkB, was examined by in situ hybridization and Northern blot. In frontal cortex, acute ECS increased BDNF mRNA approximately twofold, an effect significantly augmented by a prior course of chronic ECS treatment (10 d). In the hippocampus, the influence of chronic ECS varied between the major subfields. In the dentate gyrus granule cell layer, chronic ECS decreased the acute induction of BDNF and trkB mRNA by approximately 50%, but prolonged their expression: levels remained elevated two- to threefold 18 hr later after the last chronic ECS treatment, but returned to control 18 hr after acute ECS. In CA3 and CA1 pyramidal cell layers, chronic ECS significantly elevated the acute induction of BDNF, and tended to prolong the expression of BDNF and trkB mRNA. A similar effect was observed in layer 2 of the piriform cortex, where chronic ECS significantly increased the acute induction and prolonged the expression of BDNF and trkB mRNA. Chronic (21 d), but not acute (1 d), administration of several different antidepressant drugs, including tranylcypromine, sertraline, desipramine, or mianserin, significantly increased BDNF mRNA and all but mianserin increased trkB mRNA in hippocampus. In contrast, chronic administration of nonantidepressant psychotropic drugs, including morphine, cocaine, or haloperidol, did not increase levels of BDNF mRNA. Furthermore, chronic administration of ECS or antidepressant drugs completely blocked the down-regulation of BDNF mRNA in the hippocampus in response to restraint stress. The enhanced induction and prolonged expression of BDNF in response to chronic ECS and antidepressant drug treatments could promote neuronal survival, and protect neurons from the damaging effects of stress.

A molecular and cellular theory of depression

Abstract: Recent studies have begun to characterize the actions of stress and antidepressant treatments beyond the neurotransmitter and receptor level. This work has demonstrated that long-term antidepressant treatments result in the sustained activation of the cyclic adenosine 3',5'-monophosphate system in specific brain regions, including the increased function and expression of the transcription factor cyclic adenosine monophosphate response element-binding protein. The activated cyclic adenosine 3',5'-monophosphate system leads to the regulation of specific target genes, including the increased expression of brain-derived neurotrophic factor in certain populations of neurons in the hippocampus and cerebral cortex. The importance of these changes is highlighted by the discovery that stress can decrease the expression of brain-derived neurotrophic factor and lead to atrophy of these same populations of stress-vulnerable hippocampal neurons. The possibility that the decreased size and impaired function of these neurons may be involved in depression is supported by recent clinical imaging studies, which demonstrate a decreased volume of certain brain structures. These findings constitute the framework for an updated molecular and cellular hypothesis of depression, which posits that stress-induced vulnerability and the therapeutic action of antidepressant treatments occur via intracellular mechanisms that decrease or increase, respectively, neurotrophic factors necessary for the survival and function of particular neurons. This hypothesis also explains how stress and other types of neuronal insult can lead to depression in vulnerable individuals and it outlines novel targets for the rational design of fundamentally new therapeutic agents.