Dual transcriptional programs coordinate lipogenic and membrane stress responsive programs in C. elegans

Metabolism can affect the aging process through many mechanisms. The effects of calorie levels and the sensation of nutrient sources are powerful regulators. Other metabolic pathways may affect aging by acting as signaling or transcriptional regulators. The 1 carbon cycle has multiple links to aging, particularly through the production of the methyl donor S-adenosylmethionine (SAM). SAM is critical for epigenetic modification, which can affect many cellular processes, including aging. SAM is also important for the production of a phospholipid, phosphatidylcholine (PC), which is a major membrane component. We propose to study how one 1CC metabolite, PC, impacts aging though it’s role in a membrane stress pathway. Using a long-lived C. elegans model (sams-1) and human cell-based assays, we found that lowering PC induces a stress response in the Golgi, limiting the GTPase ARF-1.2/ARF1, which is a critical regulator of Golgi function. One effect of this stress response is the maturation of a membrane-intrinsic transcription factor, SBP-1/SREBP-1, to restore lipid homeostasis. We also found that a compensatory program is upregulated that produces an alternative ARF, arf- 1.1. to support Golgi function. We have identified at least one transcription factor, LET-607, which is also intrinsic to the membrane, as a regulator of this process. Thus, the Golgi stress response has multiple transcriptional outputs that play specific roles in correcting organelle misfunction. Finally, Golgi stress may be important in multiple neurodegenerative diseases, suggesting our studies could have a broad impact outside the aging field. Our proposal is based on data from multiple genetic screens, metabolomic studies, and other unbiased approaches. Next, our plan is to use a combination of cell biology, genetics and biochemistry several key questions. First, we will explore the basic cell biology of the Golgi stress response, which is not well understood. Second, we will determine how the LET-607 transcription factor is regulated during the stress response. These experiments will be complemented by our investigation on the molecular and biochemical basis explaining how ARF-1.1 can function when membrane conditions limit ARF-1.2. Finally, we have found that ARF-1.2 selectively disappears from the intestine in aging C. elegans. Because regulation of yolk secretion has important connections to aging, it is important to understand what regulates this loss of ARF-1.2 and how it might impact aging in sams-1 animals. Metabolites such as SAM and PC may have distinct roles in aging and stress in a variety of contexts, as these molecules can contribute to a variety of different processes. By delineating molecular mechanisms downstream of SAM and PC that affect membrane properties, we will uncover how specific aspects of 1 carbon and lipid metabolism drive changes in aging and stress.