Molecular Neurodegeneration //
Science

Scope of the research

We aim to identify and characterize molecular mechanisms underlying the pathogenesis of neurodegenerative disorders. Our aim is also to identify common mechanisms between different neurodegenerative diseases. We especially focus is on Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD).

Neurodegenerative disorders, such as AD and FTLD, are common in the aging population. However, particularly FTLD can also afflict people who still actively participate in working life. Currently, there are no available therapies to slow down or stop the pathogenesis of these diseases. In addition, biomarkers, which could be used to identify individuals at risk for developing AD or FTLD, or to predict disease progression are lacking.

The ultimate goal of our investigations is to identify new molecular targets, which partake in neurodegeneration in AD and FTLD and underlie the clinical manifestations of these diseases. We aim at understanding the specific mechanisms how and why these targets affect the pathogenic events taking place in AD or FTLD at the molecular and cellular level. This knowledge may eventually aid in the development of new predictive disease biomarkers or therapeutic strategies for AD or FTLD.

Main achievements

We have identified several new genes that modulate the risk of AD in humans. We have widely characterized their molecular mechanisms in neurodegeneration and how they influence the already known molecular players in AD pathogenesis, such as amyloid precursor protein (APP), β-amyloid (Aβ), tau, β-secretase BACE1, or presenilin-1 (PS1), a key component of the γ-secretase complex, in our cell-based and animal models and in human brain and cerebrospinal fluid (CSF) samples. Examples of these genes include seladin-1/DHCR24 and UBQLN1 (ubiquilin-1). These studies have generated novel information on the molecular pathogenic events taking place during AD.

  • We observed that down-regulation of seladin-1 increases BACE1 levels and activity through enhanced depletion of the BACE1 regulatory protein GGA3 during apoptosis (Sarajärvi et al., 2009, J Biol Chem).
  • We found that ubiquilin-1 regulates the levels and targeting of AD-associated PS1 to proteasomal degradation and intracellular inclusions called aggresomes, and thus likely affects PS1 function (Viswanathan et al., 2011, Traffic).
  • Our recent studies identified ubiquilin-1 as a novel protein regulating BACE1 levels and activity by influencing BACE1 subcellular localization (Natunen et al., 2016, Neurobiol Dis).
  • We have performed global transcriptomics analysis of human brain samples and assessed expressional changes of several AD-associated risk genes according to progression of neurofibrillary pathology (Braak staging) in human brain. The effects of these genes on the key molecular players underlying AD molecular pathogenesis, such as APP, BACE1 and tau, were also characterized in a cell-based model system (Martiskainen et al., 2015, Neurobiol Aging). These investigations have provided novel insights into the mechanisms of the AD risk genes at the molecular level.

We have performed global transcriptomics analysis of human brain samples and assessed expressional changes of several AD-associated risk genes according to progression of neurofibrillary pathology (Braak staging) in human brain. The effects of these genes on the key molecular players underlying AD molecular pathogenesis, such as APP, BACE1 and tau, were also characterized in a cell-based model system (Martiskainen et al., 2015, Neurobiol Aging). These investigations have provided novel insights into the mechanisms of the AD risk genes at the molecular level.

Research strategy and methods

We use a translational approach in our research, proceeding from different cell-based models to animal models and to patient-derived samples of AD or FTLD in our studies. We also simulate the prevailing pathological conditions in the brains of patients with AD or FTLD in our model systems.

Model systems and materials:

  • Cultures of non-neuronal and neuronal cell lines
  • Cultures of mouse primary neurons, astrocytes or microglial cells
  • Co-cultures of mouse neurons with microglial cells
  • Animal models (as research collaboration)
  • Human brain samples
  • Human cerebrospinal fluid samples

Modeling neurodegeneration-associated pathological conditions in model systems:

  • Neuroinflammation
  • Excitotoxicity
  • Oxidative stress
  • ER stress
  • Proteostatic stress

Methods:

  • Overexpression or downregulation (RNAi) of targets of interest in primary and secondary neuronal and non-neuronal cells by transfection or lentivirus-mediated transduction
  • Overexpression or downregulation (RNAi) of targets of interest in mouse hippocampus by lentivirus-mediated transduction
  • Modeling neurodegenerative-disease associated stress conditions (neuroinflammation, excitotoxicity, oxidative stress, ER stress, proteostatic stress, autophagy induction)
  • Analyses of mRNA and protein expression, half-life, and protein-protein interactions (Quantitative PCR, Western blotting, cycloheximide time course, co-immunoprecipitation, cell surface biotinylation, ELISA)
  • Enzyme activity measurements (e.g. α-, β- and γ-secretase)
  • Subcellular fractionation of cells
  • Intracellular inclusion (aggresome) analyses
  • Neuronal viability assays
  • Immunofluorescence and immunohistochemical staining of cells and tissue samples
  • Fluorescence and confocal microscopical analyses of cell morphology and subcellular localization of proteins

Current projects

  • Role of ubiquilin family proteins in molecular mechanisms of neurodegeneration. We are continuing to investigate the role of ubiquilin-1 variants in the regulation of protein trafficking to the proteasome and autophagosomes. We also assess interactions and biology of ubiquilin protein family members in the regulation of proteasomal or autophagosomal degradation of proteins.
  • Effects of ubiquilin-like proteins on neurodegeneration. We analyze the expression of ubiquilin-like proteins in human brain in relation to progressing neurodegeneneration and assess the effects of those in mechanisms of neurodegeneration during AD and FTLD pathogenesis.
  • Role of C9ORF72 gene in FTLD molecular mechanisms. We investigate the biological and pathophysiological effects of the novel FTLD-associated C9ORF72 gene on mechanisms of neurodegeneration during FTLD pathogenesis.

Selected publications

  • Kurkinen KM*, Marttinen M*, Turner L, Natunen T, Mäkinen P, Haapalinna F, Sarajärvi T, Gabbouj S, Kurki M, Paananen J, Koivisto AM, Rauramaa T, Leinonen V, Tanila H, Soininen H, Lucas FR, Haapasalo A*, Hiltunen M*. SEPT8 modulates β-amyloidogenic processing of APP by affecting the sorting and accumulation of BACE1. *Equal contribution. Journal of Cell Science. 2016 Jun 1;129(11):2224-38. doi: 10.1242/jcs.185215.

  • Natunen T*, Takalo M*, Kemppainen S, Leskelä S, Marttinen M, Kurkinen KMA, Pursiheimo JP, Sarajärvi T, Viswanathan J, Gabbouj S, Solje E, Tahvanainen E, Pirttimäki T, Kurki M, Paananen J, Rauramaa T, Miettinen P, Mäkinen P, Leinonen V, Soininen H, Airenne K, Tanzi RE, Tanila H, Haapasalo A*, Hiltunen M*. Relationship between Ubiquilin-1 and BACE1 in Human Alzheimer’s disease and APdE9 Transgenic Mouse Brain and Cell-Based Models. *Equal contribution. Neurobiology of Disease. 2016 Jan;85:187-205.

  • Haapasalo A, Remes AM. Genetic and molecular aspects of frontotemporal lobar degeneration. Review. Current Genetic Medical Reports. 2015. 3:8–182014. doi: 10.1007/s40142-014-0063-5.
  • Sarajärvi T, Marttinen M, Natunen T, Kauppinen T, Mäkinen P, Helisalmi S, Laitinen M, Rauramaa T, Leinonen V, Petäjä-Repo U, Soininen H, Haapasalo A, Hiltunen M. Genetic variation in δ-opioid receptor associates with increased β- and γ-secretase activity in the late stages of Alzheimer’s disease. Journal of Alzheimer’s Disease. 2015, 48(2):507–516.
  • Martiskainen H, Viswanathan J, Nykänen NP, Kurki M, Helisalmi S, Natunen T, Sarajärvi T, Kurkinen KM, Pursiheimo JP, Rauramaa T, Alafuzoff I, Jääskeläinen JE, Leinonen V, Soininen H, Haapasalo A, Huttunen HJ, Hiltunen M. Transcriptomics and mechanistic elucidation of Alzheimer's disease risk genes in the brain and in vitro models. Neurobiology of Aging. 2015 Feb;36(2):1221.
  • Takalo M, Haapasalo A, Martiskainen H, Kurkinen KM, Koivisto H, Miettinen P, Khandelwal VK, Kemppainen S, Kaminska D, Mäkinen P, Leinonen V, Pihlajamäki J, Soininen H, Laakso M, Tanila H, Hiltunen M. High-fat diet increases tau expression in the brain of T2DM and AD mice independently of peripheral metabolic status. Journal of Nutritional Biochemistry. 2014 Jun;25(6):634-41.
  • Viswanathan J*, Haapasalo A*, Böttcher C, Miettinen R, Kurkinen KMA, Lu A, Thomas A, Maynard CJ, Romano D, Hyman BT, Berezovska O, Bertram L, Soininen H, Dantuma NP, Tanzi RE, Hiltunen M. Alzheimer's disease-associated ubiquilin-1 regulates presenilin-1 accumulation and aggresome formation. Traffic. 2011, Mar;12(3):330-348. *Equal contribution
  • Sarajärvi T, Haapasalo A, Viswanathan J, Mäkinen P, Laitinen M, Soininen H, Hiltunen M. Down-regulation of seladin-1 increases BACE1 levels and activity through enhanced GGA3 depletion during apoptosis. The Journal of Biological Chemistry, 2009, 284(49):34433-34443.