Molecular mechanisms of neuronal autophagy
Abnormal intracellular protein deposits and damaged organelles characterize many neurodegenerative disorders. Neurons are less able to degrade abnormal proteins and damaged organelles as they become older, linking the build-up of protein deposits and organelles and the appearance of adult-onset neurodegenerative disorders.
Cells turn over cellular content by two primary mechanisms. The ubiquitin-proteasome system degrades normal monomeric proteins and polypeptides, and autophagy directs proteins and organelles to lysosomes. There are three different types of autophagy: chaperone-mediated autophagy (CMA), macroautophagy, microautophagy. CMA mediates only degradation of soluble proteins. Single protein molecules are recognized by a specific cytosolic chaperone and a receptor on the lysosomal membrane, which then facilitate translocation of the protein into the lysosomal lumen. On induction of macroautophagy, cytoplasmic content or an organelle is sequestered inside double-membrane vesicles called autophagosomes. The autophagosomes subsequently fuse to the lysosomes for degradation and recycling. In microautophagy, cytosolic content can be sequestered directly by direct invagination of the lysosomal membrane.
We focus on the physiological and pathophysiological functions of macroautophagy and microautophagy in age-associated neuronal dysfunction and neurodegeneration. Our studies strongly suggest that at least some autophagic pathways can be modified with autophagy enhancers to boost degradation of abnormal protein, resulting in improved neuronal health. The ability of autophagy enhancers to increase removal of toxic material suggests that age-associated neurodegeneration can be halted or even reversed.
Transcriptional dysregulation in unsuccessful brain aging
Cognitive impairment is a key feature of aging. It includes disturbances in memory, attention, and processing speed. Memory formation and storage proceed from synaptic activation and involve intracellular signaling cascades, gene transcription, and protein synthesis. Epigenetic mechanisms, such as chemical modifications of DNA or associated proteins, are important in modulating gene transcription and, as a result, in regulating mechanisms of memory in both normative and pathogenic aging. The precise pathways that regulate epigenetic mechanisms of memory in aging are unknown.
Phospholipids are abundant within the interior of the nucleus, but their function is not clear. Our data suggest that phospholipids target many proteins in the neuronal nucleus that epigenetically control transcription and DNA homeostasis. The goals of this project are to uncover fundamental molecular mechanisms by which phospholipids transcriptionally regulate memory and cognition in general in successful and unsuccessful aging.
Chemotherapy- and virus-induced brain damage and aging
The degenerative processes induced by some chemicals or neurotropic viruses are remarkably similar to processes in aging. Thus, the mechanisms by which neurons cope with a chemical or viral insult may be a useful model of natural aging. Understanding the common mechanisms in chemically or virally associated neurological disturbances and aging can produce insights into our understanding of aging in general. The goals of this project are to understand molecular mechanisms by which chemotherapy drugs and neurotropic viruses induce neuronal dysfunction and accelerated aging.
Development of new microscopy techniques to study neurodegeneration
Traditional analyses of fixed tissues and biochemical extracts of cells have provided useful information about neurodegenerative pathways, but they cannot determine whether observed changes are pathogenic, incidental or coping responses. We need a method to collect data longitudinally, over extended periods of time, to study neurodegeneration as it unfolds. Our automated microscope system repeatedly collects images of the same group of cultured primary neurons over extended periods. Changes within those neurons, such as protein levels and aggregation, protein and organelle clearance, induction of autophagic markers, and neuronal morphology are recorded and related to their ultimate fate (i.e., to death, survival, longevity). This information then asks an important question. Does the particular change in neurons predict changes in neuronal survival and, therefore, predict longevity or neurodegeneration? The goals of this project are to develop new imaging and analysis algorithms to dynamically study neurodegeneration.