Our lab is investigating the pathogenic mechanisms of ALS-associated proteins SOD1, FUS/TLS, profilin-1 and TDP-43. ALS (amyotrophic lateral sclerosis), also known as Lou Gehrig’s disease, is a fatal neurodegenerative disorder that targets motor neurons. Motor neuron death culminates in paralysis and eventual death, usually 2-3 years after symptom onset. To date, there is no cure or effective therapy for ALS. Our ultimate goal is to translate our basic-research findings into therapies for this devastating disease. We use a multidisciplinary approach involving biochemistry, cell biology (including iPS cell technology), biophysics and in vivo model systems for our investigations.
Many neurodegenerative disease-associated proteins become misfolded as a consequence of genetic mutations and/or altered post-translational modifications. Misfolded proteins generally exert toxic functions by impairing the quality control systems within the cell and by engaging in aberrant protein interactions. Moreover, misfolded proteins self-associate and form pathological aggregates observed in post-mortem CNS tissues from individuals with various neurodegenerative diseases. Our lab is interested in defining the misfolded conformation(s) associated with pathogenic forms of SOD1 (Rotunno, JBC, 2014), profilin-1 and FUS/TLS. We then use this information to develop small-molecule screens to identify compounds that can restore the protein’s normal conformation.
Approximately 10% of ALS cases are caused by genetic defects that are inherited. These include genetic mutations in the genes encoding SOD1, FUS/TLS, profilin-1 and TDP-43. However, a majority (~90%) of ALS cases are sporadic in nature, and the causes of sporadic ALS are unknown. We are investigating the hypothesis that SOD1 plays a role in sporadic ALS (Rotunno and Bosco, Front Cell Neurosci, 2013). This hypothesis is based on findings from our lab (Bosco, Nat Neurosci, 2010) and others showing that altered post-translational modifications within wild-type SOD1 cause this protein to misfold. We are currently investigating whether misfolded SOD1 is present in biological samples from individuals with ALS.
TDP-43 is also implicated in sporadic ALS. Pathological aggregates containing TDP-43 are present in a majority (>95%) of ALS cases (including both sporadic and familial). Moreover, TDP-43 pathology is also present in the related disease frontotemporal lobar degeneration (FTLD) as well as in other neurological disorders. We are investigating the hypothesis that a loss of TDP-43 function plays a role in ALS, and are developing a small molecule screen to ameliorate the toxic consequences of a loss of TDP-43 function.
Our lab was one of the first to demonstrate that ALS-linked FUS incorporates into stress granules under various conditions of cellular stress (Bosco, Hum Mol Genet, 2010). Stress granules are dynamic (click to watch video) stalled translational complexes that assemble in the cytoplasm in response to acute stress. Our data indicate that the incorporation of ALS-FUS into stress granules alters the functional properties of these structures (Baron, Mol Neurodegener, 2013), supporting the notion that mutant-FUS exerts a gain of toxic function with respect to stress granule assembly and dynamics. Currently, we are investigating the factors (both protein and RNA) that are incorporated into stress granules in a mutant-FUS dependent manner. We are also exploring novel responses of endogenous FUS to different stressors (e.g., hyperosmolar stress described below).
We recently discovered that FUS/TLS exhibits a robust response to hyperosmolar stress (Sama, J Cell Physiol, 2013) in that this protein translocates from the nucleus, where it normally resides, to the cytoplasm (click for video). We found that reduced expression of FUS rendered cells more susceptible to hyperosmolar stress, suggesting that endogenous FUS plays a pro-survival role under these conditions. Based on this finding and reports linking TDP-43 and C9ORF72 to osmotic stress, we are testing the hypothesis that hyperosmotic stress is novel and relevant factor in ALS pathogenesis.
FUS/TLS is a complex, multi-functional protein (Sama, Ward and Bosco, ASN Neuro, 2014). Through our investigations of FUS/TLS in ALS, we have uncovered novel findings about the normal functions of FUS/TLS. In addition to the role of FUS/TLS in hyperosmolar stress (described above; Sama, J Cell Physiol, 2013), we found that a reduction in FUS/TLS expression causes a severe defect in cellular proliferation (Ward, Cell Death & Disease, 2014). Because FUS is an important protein for cellular homeostasis, and is linked to several diseases other than ALS, we are interested in investigating the normal, vital functions of FUS/TLS in the cell.
Having discovered that mutant-FUS incorporates into stress granules, our lab has become interested in the fundamental biology associated with these assemblies. Data from our lab and others show that the constituents and properties of stress granules are largely dependent upon the stress that induces their formation. We are interested in understanding i) the factors that modulate stress granule assembly and disassembly, ii) the factors that dictate the constituents of stress granules, and iii) how the constituents of stress granules help the cell re-establish homeostasis.
Our ultimate goal is to translate our basic-research findings into therapies for ALS and related disorders. Several projects within the lab involve high-throughput small molecule screening. These screening projects are at various stages from development through publication (Ward, under revision). Most of our work is in collaboration with Dr. Marcie Glicksman at the LDDN in Cambridge, and we also use the chemical libraries available at UMMS.