Chanhee Kang highlights two papers by Baker et al. and Acosta et al. that established a role for senescent cells in age-related pathologies and revealed how the senescence-associated secretory phenotype (SASP) can influence neighbouring cells.

Ribosome-associated quality control (RQC) is a pivotal biological process that governs the fidelity of messenger RNA (mRNA) homeostasis and protein synthesis. Defects in RQC are implicated in cellular dysfunction and proteotoxicity, but their impact on aging remains elusive. Here, we show that Pelota, the ribosome rescue factor, promotes longevity and protects against age-related pathological phenotypes in multiple metazoan species. By performing a targeted genetic screen, we find that Pelota is indispensable for longevity in the nematode Caenorhabditis elegans. We show that Pelota mitigates premature senescence in cultured human cells, muscle aging in mice, and neuropathology in cellular and organoid models of Alzheimer's disease. Mechanistically, we demonstrate that Pelota maintains autophagy-mediated proteostasis, by preventing the hyperactivation of mechanistic target of rapamycin signaling. Overall, our work highlights the conserved functional significance of RQC, regulated by Pelota, in extending lifespan and protecting diverse species against age-associated disease phenotypes.

Dynamic changes in cell size are associated with development and pathological conditions, including aging. Although cell enlargement is a prominent morphological feature of cellular senescence, its functional implications are unknown; moreover, how senescent cells maintain their enlargement state is less understood. Here we show that an extensive remodeling of actin cytoskeleton is necessary for establishing senescence-associated cell enlargement and pro-inflammatory senescence-associated secretory phenotype (SASP). This remodeling is attributed to a balancing act between the SASP regulator GATA4 and the mechanosensor YAP on the expression of the Rho family of GTPase RHOU. Genetic or pharmacological interventions that reduce cell enlargement attenuate SASP with minimal effect on senescence growth arrest. Mechanistically, actin cytoskeleton remodeling couples cell enlargement to the nuclear localization of GATA4 and NF-κB via the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex. RhoU protein accumulates in mouse adipose tissue under senescence-inducing conditions. Furthermore, RHOU expression correlates with SASP expression in adipose tissue during human aging. Thus, our study highlights an unexpected instructive role of cell enlargement in modulating the SASP and reveals a mechanical branch in the senescence regulatory network. Senescent cells accumulate during aging and exhibit cell enlargement, the function of which has been unclear for decades. Here, the authors identify an antagonistic genetic circuit for hypertrophy and reveal its instructive role in modulating the SASP.

The cellular proteome determines the functional state of cells and is often skewed to direct pathological conditions. Autophagy shapes cellular proteomes primarily through lysosomal degradation of either damaged or unnecessary proteins. Here, we show that autophagy directs the senescence-specific translatome to fuel inflammation by coupling selective protein degradation with alternative splicing. RNA splicing is significantly altered during senescence, some of which surprisingly depend on autophagy, including exon 5 skipping of the translation regulator EIF4H. Systematic translatome profiling indicates that this event is key to the translational bias toward inflammation in senescence. Autophagy promotes these changes by selectively degrading the splicing regulator splicing factor proline and glutamine rich (SFPQ) via the autophagy receptor NBR1. These autophagy-centric inflammatory controls appear to be conserved during human tissue aging and cancer. Our work highlights the role of autophagy in the on-demand functional remodeling of cellular proteomes as well as the crosstalk between autophagy, alternative splicing, and inflammatory translation.

UDP-GlcNAc serves as a building block for glycosaminoglycan (GAG) chains in cartilage proteoglycans and simultaneously acts as a substrate for O-GlcNAcylation. Here, we show that transporters for UDP-GlcNAc to the endoplasmic reticulum (ER) and Golgi are significantly downregulated in osteoarthritic cartilage, leading to increased cytosolic UDP-GlcNAc and O-GlcNAcylation in chondrocytes. Mechanistically, upregulated O-GlcNAcylation governs the senescence-associated secretory phenotype (SASP) by stabilizing GATA4 via O-GlcNAcylation at S406, which compromises its degradation by p62-mediated selective autophagy. Elevated O-GlcNAcylation in the superficial layer of osteoarthritic cartilage coincides with increased GATA4 levels. The topical deletion of Gata4 in this cartilage layer ameliorates post-traumatic osteoarthritis (OA) in mice while inhibiting O-GlcNAc transferase mitigates OA by decreasing GATA4 levels. Excessive glucosamine-induced O-GlcNAcylation stabilizes GATA4 in chondrocytes and exacerbates post-traumatic OA in mice. Our findings elucidate the role of UDP-GlcNAc compartmentalization in regulating secretory pathways associated with chronic joint inflammation, providing a senostatic strategy for the treatment of OA. Here, the authors show that reduced transport of UDP-GlcNAc to the endoplasmic reticulum and Golgi leads to increased cytosolic UDP-GlcNAc and O-GlcNAcylation in chondrocytes. This, in turn, stabilizes the transcription factor GATA4, promoting the senescence-associated secretory phenotype and exacerbating osteoarthritis.

Cellular metabolism is a flexible and plastic network that often dictates physiological and pathological states of the cell, including differentiation, cancer, and aging. Recent advances in cancer metabolism represent a tremendous opportunity to treat cancer by targeting its altered metabolism. Interestingly, despite their stable growth arrest, senescent cells – a critical component of the aging process – undergo metabolic changes similar to cancer metabolism. A deeper understanding of the similarities and differences between these disparate pathological conditions will help identify which metabolic reprogramming is most relevant to the therapeutic liabilities of senescence. Here, we compare and contrast cancer and senescence metabolism and discuss how metabolic therapies can be established as a new modality of senotherapy for healthy aging.

Abstract Anabolic activity, driven by growth factor signaling, is essential for cellular activities, including cell growth, proliferation, and protein synthesis. Dysregulation of growth factor signaling has been implicated in numerous human pathological conditions, including cancer and aging. Interestingly, cancer cells and senescent cells - two completely different cell fates - are reported to have an increased anabolic activity. Here, we show endosomal condensation of a growth factor receptor as a molecular switch for such anabolic enhancement. Endosomal condensates of a growth factor receptor (ecGFR) exhibit liquid-liquid phase separation (LLPS), acting as a signaling hub locked in the ‘ON’ state by preventing their lysosomal degradation. Furthermore, we identify a regulatory circuit that operates in both cancer and senescence to facilitate the formation of ecGFR and its physicochemical properties. Pharmacological and genetic resolution of ecGFR corrects aberrant anabolism in cancer and senescence, thereby suppressing cancer growth and senescence-associated hyperinflammation in vitro as well as in vivo. Thus, our study provides a convergent anabolic core between cancer and senescence that could be exploited as a therapeutic vulnerability for human pathological conditions associated with aberrant anabolism. Citation Format: Taegyun Kim, Haebeen Choi, Taeyoung Yoon, Chanhee Kang. A cytosolic growth factor receptor serves as a convergent core of condensates for anabolic activity in cancer and senescence [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2971.

Cellular immortalization is a complex process that requires multiple genetic alterations to overcome restricting barriers, including senescence. Not surprisingly, many of these alterations are associated with cancer; two tumor suppressor pathways, the cellular tumor antigen p53 and p16‐Retinoblastoma (RB) pathways, are the best‐characterized examples, but their mutations alone are known to be insufficient to drive full immortalization. En et al. identified a role for the lamin B receptor (LBR) in promoting cellular proliferation and immortalization in p53‐ and RB‐deficient cells by maintaining their genome integrity and suppressing senescence. Thus, modulation of LBR could be exploited to treat cancer and potentially also to promote cell rejuvenation.

Cellular senescence is a crucial biological process associated with organismal aging and many chronic diseases. Here, we present a brief guide to mammalian senescence assays, including the measurement of cell cycle arrest, change in cellular morphology, senescence-associated β-galactosidase (SA-β-gal) staining, and the expression of senescence-associated secretory phenotype (SASP). This work will be useful for biologists with minimum expertise in cellular senescence assays.

Whereas cholesterol is vital for cell growth, proliferation, and remodeling, dysregulation of cholesterol metabolism is associated with multiple age-related pathologies. Here we show that senescent cells accumulate cholesterol in lysosomes to maintain the senescence-associated secretory phenotype (SASP). We find that induction of cellular senescence by diverse triggers enhances cellular cholesterol metabolism. Senescence is associated with the upregulation of the cholesterol exporter ABCA1, which is rerouted to the lysosome, where it moonlights as a cholesterol importer. Lysosomal cholesterol accumulation results in the formation of cholesterol-rich microdomains on the lysosomal limiting membrane enriched with the mammalian target of rapamycin complex 1 (mTORC1) scaffolding complex, thereby sustaining mTORC1 activity to support the SASP. We further show that pharmacological modulation of lysosomal cholesterol partitioning alters senescence-associated inflammation and in vivo senescence during osteoarthritis progression in male mice. Our study reveals a potential unifying theme for the role of cholesterol in the aging process through the regulation of senescence-associated inflammation.

The Wnt signaling pathway plays a critical role in the developmental and physiological processes of metazoans. We previously reported that the Frizzled4 (FZD4) linker domain plays an important role in Norrin binding and signaling. However, the question remains whether the FZD linker contributes to Wnt signaling in general. Here, we show that the FZD linker is involved in Wnt binding and affects downstream Wnt signaling. A FZD4 chimera, in which the linker was swapped with that of the non-canonical receptor FZD6, impairs the binding with WNT3A and suppresses the recruitment of LRP6 and Disheveled, resulting in reduced canonical signaling. A similar effect was observed for non-canonical signaling. A FZD6 chimera containing the FZD1 linker showed reduced WNT5A binding and impaired signaling in ERK, JNK, and AKT mediated pathways. Altogether, our results suggest that the FZD linker plays an important role in specific Wnt binding and intracellular Wnt signaling.

Low-density lipoprotein receptor-related protein 6 (LRP6) is a coreceptor of the β-catenin-dependent Wnt signaling pathway. The LRP6 ectodomain binds Wnt proteins, as well as Wnt inhibitors such as sclerostin (SOST), which negatively regulates Wnt signaling in osteocytes. Although LRP6 ectodomain 1 (E1) is known to interact with SOST, several unresolved questions remain, such as the reason why SOST binds to LRP6 E1E2 with higher affinity than to the E1 domain alone. Here, we present the crystal structure of the LRP6 E1E2–SOST complex with two interaction sites in tandem. The unexpected additional binding site was identified between the C-terminus of SOST and the LRP6 E2 domain. This interaction was confirmed by in vitro binding and cell-based signaling assays. Its functional significance was further demonstrated in vivo using Xenopus laevis embryos. Our results provide insights into the inhibitory mechanism of SOST on Wnt signaling.

Natural products and their derivatives historically represent alternatives to conventional synthetic molecules for pharmacotherapy, ranging from cancer chemotherapeutics to cosmetic ingredients that exert anti-aging activities. Cellular senescence is considered a main driver of skin aging, yet natural products that target skin senescence in a specific manner are not thoroughly explored. Here, we performed a focused compound screen to identify natural products that exert anti-senescence effects. We found that Isatis tinctoria, woad extracts, displayed a senolytic effect on senescent human skin fibroblasts. Furthermore, treatment with woad extracts attenuated the expression of pro-inflammatory senescence-associated secretory phenotype (SASP), showing a senostatic activity. Intriguingly, woad extracts displayed only a marginal cytotoxic effect toward senescent human lung fibroblasts. Thus, our results reveal the potential activities of woad extracts for targeting skin senescence and suggest that woad extracts could be an attractive ingredient for cosmetics to prevent skin aging.

Cellular senescence is a complex stress response implicated in aging. Autophagy can suppress senescence but is counterintuitively necessary for full senescence. Although its anti-senescence role is well described, to what extent autophagy contributes to senescence establishment and the underlying mechanisms is poorly understood. Here, we show that selective autophagy of multiple regulatory components coordinates the homeostatic state of senescence. We combined a proteomic analysis of autophagy components with protein stability profiling, identifying autophagy substrate proteins involved in several senescence-related processes. Selective autophagy of KEAP1 promoted redox homeostasis during senescence. Furthermore, selective autophagy limited translational machinery components to ameliorate senescence-associated proteotoxic stress. Lastly, selective autophagy of TNIP1 enhanced senescence-associated inflammation. These selective autophagy networks appear to operate in vivo senescence during human osteoarthritis. Our data highlight a caretaker role of autophagy in the stress support network of senescence through regulated protein stability and unravel the intertwined relationship between two important age-related processes.

Autophagy and cellular senescence are two potent tumor suppressive mechanisms activated by various cellular stresses, including the expression of activated oncogenes. However, emerging evidence has also indicated their pro-tumorigenic activities, strengthening the case for the complexity of tumorigenesis. More specifically, tumorigenesis is a systemic process emanating from the combined accumulation of changes in the tumor support pathways, many of which cannot cause cancer on their own but might still provide excellent therapeutic targets for cancer treatment. In this review, we discuss the dual roles of autophagy and senescence during tumorigenesis, with a specific focus on the stress support networks in cancer cells modulated by these processes. A deeper understanding of such context-dependent roles may help to enhance the effectiveness of cancer therapies targeting autophagy and senescence, while limiting their potential side effects. This will steer and accelerate the pace of research and drug development for cancer treatment.

Most animals face frequent periods of starvation throughout their entire life and thus need to appropriately adjust their behavior and metabolism during starvation for their survival. Such adaptive responses are regulated by a complex set of systemic signals, including hormones and neuropeptides. While much progress has been made in identifying pathways that regulate nutrient-excessive states, it is still incompletely understood how animals systemically signal their nutrient-deficient states. Here, we showed that the FMRFamide neuropeptide FLP-20 modulates a systemic starvation response in Caenorhabditis elegans. We found that mutation of flp-20 rescued the starvation hypersensitivity of the G protein β-subunit gpb-2 mutants by suppressing excessive autophagy. FLP-20 acted in AIB neurons, where the metabotropic glutamate receptor MGL-2 also functions to modulate a systemic starvation response. Furthermore, FLP-20 modulated starvation-induced fat degradation in a manner dependent on the receptor-type guanylate cyclase GCY-28. Collectively, our results reveal a circuit that senses and signals nutrient-deficient states to modulate a systemic starvation response in multicellular organisms.

Macroautophagy/autophagy is a sophisticated quality control program that limits cellular damage and maintains homeostasis, being an essential part of several lifespan-promoting interventions. However, autophagy is also necessary for full establishment of cellular senescence, a causal factor for many age-related diseases and aging. What lies ahead of us to unravel such a paradoxical role of autophagy in senescence is to identify specific targets degraded by autophagy during senescence and determine their importance in the senescence regulatory network. Recently, we developed the "Selective autophagy substrates Identification Platform (SIP)" to advance these goals, providing a rich set of autophagy substrate proteins involved in senescence. Our study demonstrated that selective autophagy coordinates the stress support networks in senescent cells by degrading multiple regulatory components, echoing its homeostatic roles in normal cells. Targeting this type of selective autophagy might provide a unique opportunity to develop non-senescence addiction-based therapeutic strategies for senotherapy by disturbing the homeostatic state of senescent cells.