Summary
The research goals of our laboratory are to investigate the cellular and molecular mechanisms underlying neurodegeneration in disorders such as Amyotrophic Lateral Sclerosis (ALS) along with other neurodegenerative and neuromuscular diseases. We hope to use these basic discoveries for future translation into potential drug discovery efforts aimed at providing novel treatments for ALS patients. In parallel with our studies of neurological disease pathophysiology, we explore the basic neurobiology of CNS glia. Our glial studies include 1) astroglia as they are regulated by neurons and as they in turn regulate synaptic transmission; and 2) oligodendroglia as they act to trophically support neurons and their long axons.
Our current research efforts include studies on the role of the nuclear pore complex, astroglia, and oligodendroglia in ALS disease pathogenesis. We have first described the defect in neuronal nuclear pore complex composition and function and astroglia in ALS and more recently have defined an expected role for oligodendroglia in neurodegeneration. We are also interested in understanding how the newly discovered C9orf72 mutation leads to ALS disease as well as frontotemporal dementia (FTD). To study these pathogenic processes, we generated the nations first large library of ALS induced pluripotent stem cells (iPSCs) that are differentiated into neurons and glial cells. We also use rodent animal models of disease as well as various in vitro organotypic systems. Overall, these innovative genetic, cellular, molecular and imaging tools (in vitro and in vivo) are employed to answer these scientific questions.
Ongoing translational efforts in the laboratory include the development of diagnostic and pharmacodynamics biomarker assays that allow us to provide better diagnosis for ALS patients and to monitor future clinical trials, respectively. These assays include the development and validation of PET imaging tracers as well as protein biomarker assays (proteomics/ELISA/SILAC). In addition, we are validating the use of iPSC derived neuron cultures as a pre-clinical screening platform for novel ALS therapeutics.
C9orf72 mutation in ALS
Varying projects in the lab are focused on the elucidation of the molecular mechanisms of the newly discovered gene mutation in C9orf72. This mutation is characterized by an expanded GGGGCC (G4C2) hexanucleotide repeat in the non-coding region of the C9orf72 gene on chromosome 9p21 and represents the most common genetic abnormality in frontotemporal dementia (FTD; 10-30%) and ALS (20-50%).
- Do astrocytes and/or oligodendrocytes exhibit RNA toxicity similarly to neurons and thereby contribute to C9orf72 pathogenesis in a non-cell autonomous fashion? (Jackie Pham and Sean Miller)
- Does synaptic dysfunction explain cognitive impairment seen in C9orf72 patients and does it explain increased susceptibility of iPS neurons to cellular stressors, such as glutamate and ER stressors? (Ileana Lorenzini and Thomas O’Donnell)
- Does the sequestration of RNA binding protein RanGAP1 lead to nuclear transport deficits of nuclear proteins, such as TDP43? (Jonathan Grima and Christopher Donnelly)
- Does the sequestration of RNA binding protein ADARB2 lead to aberrant RNA editing of neuronal signaling proteins, such as GluA2 receptors? (Emily Mendez)
Role of MCT1 as metabolic supporter in the CNS and PNS
In recent years, it has become clear that oligodendrocytes and Schwann cells support axons and are critical for their function and survival. We found that this support is at least partially by providing the energy metabolite lactate to axons via monocarboxylate transporter 1 (MCT1), a specialized transporter for lactate, pyruvate, and ketone bodies. In ALS, oligodendrocytes are injured and MCT1 expression is reduced. Attenuation of MCT1 in oligodendrocytes produces axonal degeneration and likely contributes to axon and neuron degeneration in ALS. Additionally, MCT1 in the peripheral nerves, both in Schwann cells and perineurial cells, is important for regeneration following injury, as attenuation of MCT1 leads to delayed regeneration from sciatic nerve crush. Our laboratory continues to evaluate the mechanisms of oligodendrocyte injury in ALS as well as Multiple Sclerosis (Sean Miller, Ying Li and Thomas Philips), transfer of metabolic energy from oligodendrocytes to axons (Thomas Philips and Brett Morrison), and role of MCT1 and other metabolic transporters in nerve regeneration (Brett Morrison) as well as aging (Thomas Philips), with the ultimate goal of developing novel therapeutics for both ALS and peripheral neuropathies.
Role of oligodendrocytes in ALS disease pathogenesis
Recent data from our laboratory provide evidence that oligodendrocytes and oligodendrocyte precursor cells play a significant role in ALS pathogenesis. Using rodent ALS animal models, ALS patient-specific induced pluripotent stem (iPS) cells differentiated into oligodendrocytes and chimeric brains, we are trying to understand the molecular mechanisms of this oligodendrocyte involvement in ALS disease onset and progression and determine how oligodendrocytes cause motor neuron degeneration. (Ying Li)
Astrocytes are no longer considered the supporting cells of the brain, but are recognized to be actively participating in numerous important brain functions. Similarly to the presence of multiple sub types of neurons, it has recently become recognized that different subtypes of astrocytes exist to fulfill the multitude of these different tasks. Our laboratory has identified heterogenous populations of astrocytes in both the cortex and the spinal cord of mice, which differ in their genetic signature as determined by RNA seq analyses as well as in their protein composition obtained via Mass Spectrometry proteomics analyses. Studies are ongoing to determine whether these subtypes of astrocytes have different susceptibilities to neuronal injury in both acute and chronic neurodegenerative diseases (Sean Miller).
Astrocyte-Blood brain barrier connection: Role in disease pathogenesis
Astrocytes are known to be critical components of the blood brain barrier. They enwrap the vasculature through end-feet processes providing metabolic support to neurons. During the course of amyotrophic lateral sclerosis (ALS), astrocytes and blood vessels display changes in morphology and function. Our laboratory examines in detail, the astrocyte structure during normal and chronic motor neuron degeneration using highly specific inducible transgenic astroglial reporter mice. Confocal imaging analysis and three-dimensional (3D) reconstruction are methods used to show how protoplasmic astrocytes undergo vascular and synaptic rearrangements during the course of ALS.
Biomarker development for ALS diagnosis and therapeutic monitoring
In addition to our interests in translating basic discoveries into therapeutic development, we also have several projects ongoing aimed at the development of biomarkers to diagnose disease but also to pharmacodynamically monitor therapeutic efficacy during clinical trials. These biomarkers include PET ligands for the metabotropic glutamate receptor mGluR5 (Lyle Ostrow), PET ligands for excitatory amino acid transporter EAAT2 (Rita Sattler) and protein biomarkers to monitor drug efficacy for C9orf72 therapeutics (measurements of RAN translation peptides and CNS secreted proteins in patient CSF; Lindsey Hayes, Jeff Rothstein and Rita Sattler).