Pembe H. Ozdinler, Ph.D. - US grants

There are thousands of different neuron populations in our cerebral cortex, but in neurodegenerative diseases only a select neuron population show primary vulnerability and undergo progressive degeneration. Corticospinal motor neurons (CSMN) are large pyramidal neurons that are located in layer V of the motor cortex. Their cellular structure is very unique and they function as the spokes personof the cerebral cortex for the initiation and modulation of movement. Voluntary movement is the act of a clever and well-informed mind. Therefore CSMN receive information from numerous neurons, including long-distance projection and local circuitry neurons. CSMN's unique ability to integrate and translate this information into one signal towards spinal cord targets sets it apart from other cortical neurons. Therefore its degeneration has severe consequences that lead to various movement disorders. There is a developing need to understand the basis of CSMN degeneration in diseases. However, identification and visualization of CSMN is not easy as they are embedded among thousands of other neuron populations within the cerebral cortex. We recently generated a novel reporter line, the UCHL1-eGFP mice, in which CSMN are genetically labeled in the motor cortex. eGFP expression under the control of UCHL1 promoter is stable, persistent up to P800 in vivo, and is restricted to CSMN in the motor cortex. CSMN identity of eGFP+ neurons in the motor cortex are identified by anatomy, retrograde labeling, molecular marker expression profile and electrophysiological analysis. This reporter line offers many unique advantages; a) we can for the first time visualize CSMN without any need for a retrograde labeling surgery; b) CSMN can be purified by FACS- mediated approaches at different stages in life; c) the cellular and molecular mechanisms that are responsible for CSMN vulnerability and degeneration can be studied in detail and with precision; d) most importantly this novel reporter line can be crossed to various mouse models of movement disorders to investigate the biology of CSMN with respect to disease. In this proposal, our goal is to bring visual clarity to CSMN in various mouse models of motor neuron diseases. We will be crossing UCHL1-eGFP mice with the recently identified mouse models that show potential involvement of upper motor neuron degeneration in disease pathology. Due to time limitations of R21 grant, we will characterize the timing and extent of CSMN degeneration in a limited number of mouse models, such as the Tdp43A315T and Alsin KO mice. The tools we generate and the approach we develop will help generation and characterization of other reporter mouse models, and will improve our efforts of understanding the cellular and molecular mechanisms behind CSMN vulnerability and degeneration.

Since neurons do not divide, and dilute the cytoplasm with every division, they need to have better controls over their protein content and protein turnover mechanisms. It is not surprising that almost all neurodegenerative diseases display protein accumulations, deposits, and aggregates. Even though the proteins that form aggregates show variation among diseases, there may be some common underlying causes. One of the mechanisms neurons use to control protein turnover is the ubiquitin proteosome system (UPS), which depends on the availability of free ubiquitin. Failure in UPS function results in protein clearance defects, ER-stress, increased autophagy and cellular degeneration. Ubiquitin carboxy-terminal hydrolase L1 (UCHL1) is a unique DUB with both ligase and hydrolase activities and it is gaining much attention after identification of its unique role in maintaining the free ubiquitin levels inside the neurons. Mutations in the UCHL1 gene is linked both to movement disorders in patients with Parkinson's disease, and more recently in early neurodegeneration which involves the upper motor neurons in the cerebral cortex. Building evidence also show reduced levels of UCHL1 protein in the brains of patients with neurodegenerative diseases. In this proposal, we will focus on upper motor neurons, and investigate the role of UCHL1 on the health and stability of this neuron population. We consider upper motor neurons as the spokespersonof the cerebral cortex for the motor neuron circuitry, and their degeneration leads to various neurodegenerative diseases such as hereditary spastic paraplegia, primary lateral sclerosis and they degenerate together with spinal motor neurons in amyotrophic lateral sclerosis. This proposal will bring a mechanistic insight into upper motor neuron degeneration and will reveal the role of UCHL1, and more broadly the function of improper UPS on the health and stability of upper motor neurons.

Abstract: Recent developments in chemistry, genetics, and biology revealed that many of the age-related neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS), Alzheimer's disease, and ALS/FTD share protein accumulation as the common cause of neuropathology. In addition, the number and kinds of compounds generated within the last years have exponentially increased. However, these developments in science have not yet successfully translated into effective drug discoveries for patients. This proposal is a collaborative project between the Silverman and Ozdinler Labs, blending expertise in medicinal chemistry and selective neuronal vulnerability, respectively. In an effort to expedite drug discovery and to identify novel compounds that can move into clinical trials for ALS and age-related disorders, which develop in part because of protein aggregation, such as Alzheimer's disease, we have developed a novel strategy and a strong team effort. This strategy also could, more broadly, ameliorate other neurodegenerative diseases in which voluntary movement is affected and in which protein aggregation is a major underlying cause. Dr. Silverman discovered several compounds that inhibit protein aggregation in cells and that have favorable pharmacokinetic properties, and Dr. Ozdinler developed a novel in vitro and in vivo preclinical drug screening/verification platform using the improved health of upper motor neurons (UMNs) that become diseased from different underlying factors, as the read-out. Recent discoveries from the Ozdinler group reveal the importance of improving UMN health early in the disease and that maintaining UMN health is crucial for effective drug discovery efforts. It is unfortunate that this important neuron population has never before been considered in preclinical studies, even for diseases that are identified by their selective and progressive degeneration. This proposal will develop the first preclinical platform that utilizes diseased UMNs for the assessment of novel compounds generated in the Silverman lab that inhibit protein aggregation and improve the health of diseased UMNs both in vitro and in vivo. Upon completion of this proposal, we will move the field forward along two different avenues by developing a new preclinical assay that incorporates UMN health as the read-out, and by identifying novel drugs for age-related neurodegenerative diseases that develop from problems with protein aggregation .

ABSTRACT Our collaborative efforts between the Ozdinler and Silverman Laboratories began to reveal the presence of small molecules that can reduce protein aggregation and improve the health of upper motor neurons that are diseased due to misfolded SOD1 toxicity and TDP-43 pathology. We are setting the stage for a cell-based and mechanism-focused drug discovery effort that utilizes upper motor neuron health as a readout. Recently, we also revealed the importance of ion channel homeostasis for upper motor neuron stability and how cortical connectivity is an important aspect of their health and function. Here, we apply to acquire a new equipment, which will allow us to assay and investigate potential improvements in cortical connectivity upon compound administration. Current studies investigate the stability and the cellular integrity of upper motor neurons by studying at cell/neuron structure. However, it is most desirable to reveal whether compound treatments also lead to improved cortical connectivity and function. Novel equipment, which measure field potentials, propagation of connectivity within different regions of the brain at a layer and even at a cellular level resolution has the potential to add tremendous impact to the RO1 grant we currently have. As we continue our investigations on small molecule controls over upper motor neuron health and stability, ?via reduced protein aggregation?, we believe that investigation of their neuronal activity at a cellular level, and more broadly within the cortical network, will have an immense impact on our proposal.