Uncoupling the Trade-Off between Somatic Proteostasis and Reproduction in Caenorhabditis elegans Models of Polyglutamine Diseases

Mammary gland, skin and soft tissue tumors in pet cats: findings of the feline tumors collected from 2002 to 2022

Introduction

Cancer is a leading cause of death in cats, and the rate of such disease has been increasing recently. Nonetheless, feline oncology represents an important area of study not only for the health and wellbeing of cats but also for human health since various types of cancer in cats share similarities to those found in humans. Therefore, epidemiological studies on feline oncology may suggest environmental and genetic factors contributing to cancer in cats, which can eventually be translated to improve human cancer care.

Method

To provide an initial understanding of the epidemiology of feline neoplasms, a descriptive study was undertaken using a dataset documenting cases of feline cancer gathered from the Liguria region (northwest Italy) spanning from 2002 to 2022. The database includes tumor location, morphological codes of the International Classification of Diseases for Oncology, 3rd Edition (ICD-O-3), feline's breed, sex, neuter status, date of birth, date of diagnosis, national territorial unit code of the town of the owner's residence, and an alphanumeric string uniquely identifying the owner's surname.

Results and discussion

The dataset involves a population of 4,399 cats, including 3,195 females (1,425 neutered) and 1,204 males (750 neutered). Our results indicate that mammary gland tumors are the most represented tumors in the female population, while soft tissue and skin cancers appear to have a higher abundance in the male population during the periods investigated (2002-2022). Moreover, Poisson regression analysis showed that not neutered female cats have a significantly increased risk of developing mammary gland tumors compared to the neutered female population [proportional morbidity ratio (PMR) neutered vs. not neutered = 0.58, 95% CI: 0.47-0.72]; meanwhile, for both sexes, for soft tissue and skin tumors, being neutered appears to be a risk factor (PMR neutered vs. not neutered = 2.26, 95% CI: 1.86-2.73; PMR neutered vs. not neutered = 1.16, 95% CI: 0.89-1.51). Finally, the evaluation of the Ligurian municipalities pollution, based on wild boars data (i.e., biomonitors), which coexisted with cats, was correlated to cancer development for all the tumors investigated (in polluted areas, estimated PMRs ranged from 42.61 to 80.13, 95% CI: 29.94-105.11). Overall, the data presented here suggest the use of the feline population as a possible animal model for human health, i.e., sentinel.

A unified framework for evolutionary genetic and physiological theories of aging

Why and how we age are 2 intertwined questions that have fascinated scientists for many decades. However, attempts to answer these questions remain compartmentalized, preventing a comprehensive understanding of the aging process. We argue that the current lack of knowledge about the evolution of aging mechanisms is due to a lack of clarity regarding evolutionary theories of aging that explicitly involve physiological processes: the disposable soma theory (DST) and the developmental theory of aging (DTA). In this Essay, we propose a new hierarchical model linking genes to vital rates, enabling us to critically reevaluate the DST and DTA in terms of their relationship to evolutionary genetic theories of aging (mutation accumulation (MA) and antagonistic pleiotropy (AP)). We also demonstrate how these 2 theories can be incorporated in a unified hierarchical framework. The new framework will help to generate testable hypotheses of how the hallmarks of aging are shaped by natural selection.

Mortality and heavy metals environmental exposure: a study in dogs

Introduction

Dogs are human companions and share environmental conditions with their owners. Epidemiological studies have shown that dogs seem to be good sentinel animals for the association of diseases and/or mortality provoked by chronic exposure to heavy metals (Cd, Pb).

Methods

In the present work, we analyze the registered death cases and population from the National Canine Registry from 2020 to 2022, involving a dog population of 582,564 and 17,507 deaths. The mortality rate in male and not-purebred dogs is higher than in female and purebred dogs, respectively. The mortality cases were cross-referenced with the environmental pollution data relating to the concentration of Cd and Pb detected, between 2012 and 2022, in the various municipalities of the Liguria region. We then calculated SMR (Standardized Mortality Rate) throughout the region and found that mortality increases from the eastern to the western Ligurian coast.

Results and discussion

We observed that the most polluted areas present the highest SMRs (IRR = 1.36, 95%CI: from 1.31 to 1.41). Considering dog ages, we found that mortality in young dogs is not affected by pollution, while mortality in old dogs (10-20 years old) is heavily affected by it (IRR = 8.97, 95%CI from 8.09 to 9.93). In conclusion, the data suggest the importance of canine health and biomonitor studies and provide a basis for future research involving both animal and human health.

Gonadotropin-releasing hormone-like receptor 2 inversely regulates somatic proteostasis and reproduction in Caenorhabditis elegans

The quality control machinery regulates the cellular proteome to ensure proper protein homeostasis (proteostasis). In Caenorhabditis elegans, quality control networks are downregulated cell-nonautonomously by the gonadal longevity pathway or metabolic signaling at the onset of reproduction. However, how signals are mediated between the gonad and the somatic tissues is not known. Gonadotropin-releasing hormone (GnRH)-like signaling functions in the interplay between development and reproduction and have conserved roles in regulating reproduction, metabolism, and stress. We, therefore, asked whether GnRH-like signaling is involved in proteostasis collapse at the onset of reproduction. Here, we examine whether C. elegans orthologues of GnRH receptors modulate heat shock survival. We find that gnrr-2 is required for proteostasis remodeling in different somatic tissues during the transition to adulthood. We show that gnrr-2 likely functions in neurons downstream of the gonad in the gonadal-longevity pathway and modulate the somatic regulation of transcription factors HSF-1, DAF-16, and PQM-1. In parallel, gnrr-2 modulates egg-laying rates, vitellogenin production, and thus reproductive capacity. Taken together, our data suggest that gnrr-2 plays a GnRH-associated role, mediating the cross-talk between the reproduction system and the soma in the decision to commit to reproduction.

The aging proteostasis decline: From nematode to human

The aging proteostasis decline manifests in a failure of aging cells and organisms to properly respond to proteotoxic challenges. This proteostasis collapse has long been considered a hallmark of aging in nematodes, and has recently been shown to occur also in human cells upon entry to senescence, opening the way to exploring the phenomenon in the broader context of human aging. Cellular senescence is part of the normal human physiology of aging, with senescent cell accumulation as a prominent feature of aged tissues. Being highly resistant to cell death, senescent cells, as they accumulate, become pro-inflammatory and promote disease. Here we discuss the causes of human senescence proteostasis decline, in view of the current literature on nematodes, on the one hand, and senescence, on the other hand. We review two major aspects of the phenomenon: (1) the decline in transcriptional activation of stress-response pathways, and (2) impairments in proteasome function. We further outline potential underlying mechanisms of transcriptional proteostasis decline, focusing on reduced chromatin dynamics and compromised nuclear integrity. Finally, we discuss potential strategies for reinforcing proteostasis as a means to improve organismal health and address the relationship to senolytics.

Cell-Nonautonomous Regulation of Proteostasis in Aging and Disease

The functional health of the proteome is determined by properties of the proteostasis network (PN) that regulates protein synthesis, folding, macromolecular assembly, translocation, and degradation. In eukaryotes, the PN also integrates protein biogenesis across compartments within the cell and between tissues of metazoans for organismal health and longevity. Additionally, in metazoans, proteome stability and the functional health of proteins is optimized for development and yet declines throughout aging, accelerating the risk for misfolding, aggregation, and cellular dysfunction. Here, I describe the cell-nonautonomous regulation of organismal PN by tissue communication and cell stress-response pathways. These systems are robust from development through reproductive maturity and are genetically programmed to decline abruptly in early adulthood by repression of the heat shock response and other cell-protective stress responses, thus compromising the ability of cells and tissues to properly buffer against the cumulative stress of protein damage during aging. While the failure of multiple protein quality control processes during aging challenges cellular function and tissue health, genetic studies, and the identification of small-molecule proteostasis regulators suggests strategies that can be employed to reset the PN with potential benefit on cellular health and organismal longevity.

XBP-1 Remodels Lipid Metabolism to Extend Longevity

The endoplasmic reticulum unfolded protein response (UPRER) is a cellular stress response that maintains homeostasis within the secretory pathway, regulates glucose and lipid metabolism, and influences longevity. To ask whether this role in lifespan determination depends upon metabolic intermediaries, we metabotyped C. elegans expressing the active form of the UPRER transcription factor XBP-1, XBP-1s, and found many metabolic changes. These included reduced levels of triglycerides and increased levels of oleic acid (OA), a monounsaturated fatty acid associated with lifespan extension in C. elegans. Here, we show that constitutive XBP-1s expression increases the activity of lysosomal lipases and upregulates transcription of the Δ9 desaturase FAT-6, which is required for the full lifespan extension induced by XBP-1s. Dietary OA supplementation increases the lifespan of wild-type, but not xbp-1s-expressing animals and enhances proteostasis. These results suggest that modulation of lipid metabolism by XBP-1s contributes to its downstream effects on protein homeostasis and longevity.

Methods to Study Changes in Inherent Protein Aggregation with Age in Caenorhabditis elegans

In the last decades, the prevalence of neurodegenerative disorders, such as Alzheimer's disease (AD) and Parkinson's disease (PD), has grown. These age-associated disorders are characterized by the appearance of protein aggregates with fibrillary structure in the brains of these patients. Exactly why normally soluble proteins undergo an aggregation process remains poorly understood. The discovery that protein aggregation is not limited to disease processes and instead part of the normal aging process enables the study of the molecular and cellular mechanisms that regulate protein aggregation, without using ectopically expressed human disease-associated proteins. Here we describe methodologies to examine inherent protein aggregation in Caenorhabditis elegans through complementary approaches. First, we examine how to grow large numbers of age-synchronized C. elegans to obtain aged animals and we present the biochemical procedures to isolate highly-insoluble-large aggregates. In combination with a targeted genetic knockdown, it is possible to dissect the role of a gene of interest in promoting or preventing age-dependent protein aggregation by using either a comprehensive analysis with quantitative mass spectrometry or a candidate-based analysis with antibodies. These findings are then confirmed by in vivo analysis with transgenic animals expressing fluorescent-tagged aggregation-prone proteins. These methods should help clarify why certain proteins are prone to aggregate with age and ultimately how to keep these proteins fully functional.

Misfolding and aggregation of nascent proteins: a novel mode of toxic cadmium action in vivo

Cadmium is a highly poisonous metal and a human carcinogen, but the molecular mechanisms underlying its cellular toxicity are not fully understood. Recent findings in yeast cells indicate that cadmium exerts its deleterious effects by inducing widespread misfolding and aggregation of nascent proteins. Here, we discuss this novel mode of toxic heavy metal action and propose a mechanism by which molecular chaperones may reduce the damaging effects of heavy metal ions on protein structures.

Dietary-Induced Signals That Activate the Gonadal Longevity Pathway during Development Regulate a Proteostasis Switch in Caenorhabditis elegans Adulthood

Cell-non-autonomous signals dictate the functional state of cellular quality control systems, remodeling the ability of cells to cope with stress and maintain protein homeostasis (proteostasis). One highly regulated cell-non-autonomous switch controls proteostatic capacity in Caenorhabditis elegans adulthood. Signals from the reproductive system down-regulate cyto-protective pathways, unless countered by signals reporting on germline proliferation disruption. Here, we utilized dihomo-γ-linolenic acid (DGLA) that depletes the C. elegans germline to ask when cell-non-autonomous signals from the reproductive system determine somatic proteostasis and whether such regulation is reversible. We found that diet supplementation of DGLA resulted in the maintenance of somatic proteostasis after the onset of reproduction. DGLA-dependent proteostasis remodeling was only effective if animals were exposed to DGLA during larval development. A short exposure of 16 h during the second to fourth larval stages was sufficient and required to maintain somatic proteostasis in adulthood but not to extend lifespan. The reproductive system was required for DGLA-dependent remodeling of proteostasis in adulthood, likely via DGLA-dependent disruption of germline stem cells. However, arachidonic acid (AA), a somatic regulator of this pathway that does not require the reproductive system, presented similar regulatory timing. Finally, we showed that DGLA- and AA-supplementation led to activation of the gonadal longevity pathway but presented differential regulatory timing. Proteostasis and stress response regulators, including hsf-1 and daf-16, were only activated if exposed to DGLA and AA during development, while other gonadal longevity factors did not show this regulatory timing. We propose that C. elegans determines its proteostatic fate during development and is committed to either reproduction, and thus present restricted proteostasis, or survival, and thus present robust proteostasis. Given the critical role of proteostatic networks in the onset and progression of many aging-related diseases, such a choice could impact susceptibility to protein misfolding diseases later in life.