From transport to transcription- the nuclear pore complex as a conduit for metabolic longevity signaling

Abstract

The Nuclear Pore Complex (NPC) is the sole gatekeeper between the nucleus and cytoplasm; therefore, its function is critical throughout life. One conserved biomarker of aging is the loss of nuclear membrane integrity, which can be seen in the increased leakiness and instability of the NPC. An unbiased genetic screen performed by our lab in Caenorhabditis elegans (C. elegans) found that NPC proteins (nucleoporins/Nups) are required for the pro-longevity biguanide drug, metformin, to inhibit the mTOR growth pathway. Connecting NPC function to this genetic pathway, treatment with biguanides also leads to restricted passive transport through the NPC in human cells– reverting it to a more youthful state. How the physiological modification of Nups affects longevity, and the upstream or downstream effect of the NPC on pro-longevity mechanisms, is a new and exciting area of research. In our first study, we leverage a passive transport model in living cells to further clarify the mechanism of biguanide passive transport restriction of the NPC. We find not only biguanides, but multiple mitochondrial electron transport chain (ETC) inhibitors restrict passive nucleocytoplasmic transport. Expression of O-GlcNac transferase (OGT) is significantly decreased in biguanide treated cells, leading to a decrease in global O-GlcNAcylation levels, and importantly locally reducing O-GlcNAcylation of Nup98. Further, inhibition OGT is sufficient to restrict NPC passive transport and upregulation of O-GlcNAcylation alone reverses biguanide mediated effects on nuclear permeability. These findings reveal that O-GlcNAc serves as a mitochondrial–nuclear signal, and that altered mitochondrial energetics, driven by ETC inhibition, lead to rapid changes in nucleocytoplasmic transport in human cancer cells through post-translational modification of the NPC. In our second study, we discover that CeNup153 is one of the select nucleoporins (Nups) required for biguanide mediated lifespan extension in C. elegans. CeNup153 has several roles within the nucleus, including passive transport, active transport, and chromatin organization. CeNup153 is also necessary for starvation and daf-2 mutant pro-longevity pathways, but how CeNup153 activity is altered, as well as the specific mechanisms by which CeNup153 is required to promote longevity, were not previously investigated. Here, we demonstrate that biguanide treatment increases CeNup153 expression during aging, and that CeNup153 overexpression alone is sufficient to extend lifespan. We identify CeNup153 dependent biguanide-activated or repressed genes- and find many are within pro-longevity pathways. Interestingly, one of the top differentially expressed genes (DEGs) elo-2 was previously found in our lab to be part of a biguanide longevity pathway involving ether lipogenesis. Linking these pathways, we find that CeNup153 mediated lifespan extension requires expression of these lipid biosynthesis genes. Furthermore, we show that CeNup153 binds directly to the promoter of lipid metabolism genes fard-1, elo-2, and lbp-8, supporting a model in which CeNup153 promotes longevity through epigenetic regulation of lipid metabolism.