Frontotemporal Lobar Degeneration (FTLD) is the second most common cause of presenile onset dementia after Alzheimer’s disease. Recent groundbreaking work supports a major role for the RNA-binding protein (RBP) TDP-43 in FTLD and other major age-related neurological diseases, including Amyotrophic Lateral Sclerosis (ALS) and Alzheimer’s disease. TDP-43 is a ubiquitously expressed, largely nuclear protein in healthy cells. In disease, aberrant localization and aggregation of TDP-43 protein are found in affected neurons 1 and disease-causing mutations in TDP-43 have been identified in both FTLD and ALS patients (reviewed in 2). Nevertheless, how TDP-43 contributes to disease remains unclear.
TDP-43’s relocalization from the nucleus to the cytoplasm in disease affected neurons raises a fundamental, unanswered question: is disease due to a loss of nuclear function, gain of cytoplasmic function, or a combination of the two? Since TDP-43 exhibits nuclear/cytoplasmic shuttling ability, it is likely that TDP-43 has important cytoplasmic functions, as has been described for other nuclear RBPs, such as Sex-lethal 3. Indeed, recent genome-wide studies 4,5 revealed that TDP-43 binding sites are also found in mRNA 3’ UTRs, a key region for cytoplasmic regulation of translation by RBPs. Taken together, available data support the idea that TDP-43 may regulate translation of a subset of mRNAs and suggest that aberrant translational regulation by TDP-43 could play an important role in promoting neurodegeneration and disease.
Here I propose to investigate potential cytoplasmic functions of TDP-43 in mRNA-specific translational control in neurons. In my thesis project I aim specifically to:
- Identify mRNAs whose translation is regulated by TDP-43 in neuronal cells
- Determine which mRNAs are bona fide in vivo translational targets of TDP-43 in mice
- Analyze the translational control mechanism used by TDP-43 on its neuronal targets
To achieve these aims I will use a combination of genome-wide and molecular approaches, many of which I have already previously established during my diploma thesis. By first searching for candidates in neuronal cell culture using polysome profiling, I will be able to easily screen for neuronal mRNA targets and rule out false positives. Subsequent focused studies in mouse will allow validation of specific targets in vivo and exploration of the relevance of targets to disease. Through a combination of cell-based assays and cell-free in vitro translation methods, insight into the underlying molecular mechanism will be obtained.
Through this study, I hope to elucidate TDP-43’s effects on translation of specific neuronal mRNAs. I expect my findings to greatly enhance our understanding of TDP-43’s neuronal functions, both in health and disease. Moreover, this approach has the potential to identify new targets for therapeutic development to treat these devastating diseases.