Novel treatment strategies for chronic kidney disease: insights from the animal kingdom

Many of the >2 million animal species that inhabit Earth have developed survival mechanisms that aid in the prevention of obesity, kidney disease, starvation, dehydration and vascular ageing; however, some animals remain susceptible to these complications. Domestic and captive wild felids, for example, show susceptibility to chronic kidney disease (CKD), potentially linked to the high protein intake of these animals. By contrast, naked mole rats are a model of longevity and are protected from extreme environmental conditions through mechanisms that provide resistance to oxidative stress. Biomimetic studies suggest that the transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) offers protection in extreme environmental conditions and promotes longevity in the animal kingdom. Similarly, during months of fasting, immobilization and anuria, hibernating bears are protected from muscle wasting, azotaemia, thrombotic complications, organ damage and osteoporosis - features that are often associated with CKD. Improved understanding of the susceptibility and protective mechanisms of these animals and others could provide insights into novel strategies to prevent and treat several human diseases, such as CKD and ageing-associated complications. An integrated collaboration between nephrologists and experts from other fields, such as veterinarians, zoologists, biologists, anthropologists and ecologists, could introduce a novel approach for improving human health and help nephrologists to find novel treatment strategies for CKD

Hypothesis of the basic biological sense of cancer revisited: a putative explanation of Peto's paradox

The conventional interpretation of cancer, summarized in the unified genetic theory of carcinogenesis, assumes that the malignant cell is the anatomical and physiological unit of cancer. This assumption means that any evolutionary increase in the number of cells (and thus body size) should lead to a higher tumor incidence since the population at risk is higher. However, the available data fail to support this prediction: most animals, in particular most mammals, exhibiting wide differences in body size and lifespan, from the mouse to the blue whale, display a roughly similar tumor incidence. This unexpected lack of correlation between body size, lifespan and cancer is usually called Peto?s paradox and it has intrigued theoretical oncologists for decades.In this essay, we attempt to offer a putative explanation of this paradox based on the notion that the unit at risk of carcinogenesis is actually the tissue or organ rather than the individual cell. In turn, this notion is based on a different interpretation of neoplastic diseases that we proposed some years ago and that has been called the hypothesis of the biological sense of cancer. This hypothesis was based on the observation that throughout the animal kingdom, cancer seems to arise only in organs and tissues (or parts of them) that have experienced a significant decrease in the regenerative ability, and this would occur when a critical proportion of their cells have partially or wholly lost that capacity. In such a case, if an organism or an organ were x times larger than another one, the probability that its regenerative capacity is critically diminished would be x times lower, because an x times greater number of cells would have to be affected to depress that capacity. This lower probability would balance the proportionally higher number of their cells that could be transformed and this would explain why the blue whale displays no greater risk of developing cancer than the mouse by unit of time. However, since big animals tend to live y times longer than small ones, it remains to explain why both animals may display a similar tumor incidence by lifespan. The concept of mass-specific basal metabolic rate (msBMR) can account for this problem since msBMR diminishes with body weight as much as lifespan increases meaning that the time for individual cells to get both the natural decline in regenerative ability and potential neoplastic mutations should be, in the big animal, y times slower than in the small one. This could explain why the tumor incidence in blue whales along their long lifespan may be not higher than that observed in mice along their short life.Fil: Bustuoabad, Oscar David. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Ruggiero, Raul Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentin

A PRELIMINARY INVESTIGATION INTO THE EXTENDED LIFESPAN OF BAT SPECIES: THE RELATIONSHIP BETWEEN THE EXTRACELLULAR MATRIX PROTEIN HAS2 AND LONGEVITY

Investigation into physiological and molecular factors influencing the extended lifespan of long-lived species significantly contributes to clinical research aimed at improving the lives of humans. Bats have a significantly longer lifespan than other mammals of similar size and have not been recorded to develop cancer. The longevity and anti-cancer properties displayed by bats are features shared by another well-studied mammal, the naked mole rat. The naked mole rat is currently the longest living rodent with a maximum lifespan of over 30 years, and the species exhibits a novel anti-cancer mechanism involving the rapid production of hyaluronan. The naked mole rat has a unique sequence of hyaluronan synthase 2 (HAS2) which rapidly produces high molecular mass hyaluronan and contributes to reduced activity of hyaluronan degrading enzymes. Known genomic sequences of several species of bats were analyzed to determine differences in amino acid sequence for the HAS2 gene. Furthermore, RNA extracted from captured bats was subjected to real-time polymerase chain reaction to measure the expression level of HAS2 in various tissues. Genomic sequence analysis revealed that the bat species examined did not have the same amino acid substitutions in HAS2 as the naked mole rat. Real-time PCR trials using multiple primers designed to be specific for the HAS2 region resulted in inconclusive data. Therefore, gene expression analysis conclusions cannot be made until successful HAS2 primers are generated to amplify the HAS2 region. Further research needs to be directed towards determining alternative methods to study the longevity and anti-cancer mechanisms bats possess

Independent evolution of pain insensitivity in African mole-rats: origins and mechanisms

The naked mole-rat (Heterocephalus glaber) is famous for its longevity and unusual physiology. This eusocial species that lives in highly ordered and hierarchical colonies with a single breeding queen, also discovered secrets enabling somewhat pain-free living around 20 million years ago. Unlike most mammals, naked mole-rats do not feel the burn of chili pepper's active ingredient, capsaicin, nor the sting of acid. Indeed, by accumulating mutations in genes encoding proteins that are only now being exploited as targets for new pain therapies (the nerve growth factor receptor TrkA and voltage-gated sodium channel, Na(V)1.7), this species mastered the art of analgesia before humans evolved. Recently, we have identified pain insensitivity as a trait shared by several closely related African mole-rat species. One of these African mole-rats, the Highveld mole-rat (Cryptomys hottentotus pretoriae), is uniquely completely impervious and pain free when confronted with electrophilic compounds that activate the TRPA1 ion channel. The Highveld mole-rat has evolved a biophysical mechanism to shut down the activation of sensory neurons that drive pain. In this review, we will show how mole-rats have evolved pain insensitivity as well as discussing what the proximate factors may have been that led to the evolution of pain-free traits

‘Extreme’ Organisms and the Problem of Generalization: Interpreting the Krogh Principle

Many biologists appeal to the so-called Krogh principle when justifying their choice of experimental organisms. The principle states that “for a large number of problems there will be some animal of choice, or a few such animals, on which it can be most conveniently studied”. Despite its popularity, the principle is often critiqued for implying unwarranted generalizations from optimal models. We argue that the Krogh principle should be interpreted in relation to the historical and scientific contexts in which it has been developed and used. We interpret the Krogh Principle as a heuristic, i.e., as a recommendation to approach biological problems through organisms where a specific trait or physiological mechanism is expected to be most distinctively displayed or most experimentally accessible. We designate these organisms “Krogh organisms.” We clarify the differences between uses of model organisms and non-standard Krogh organisms. Among these is the use of Krogh organisms as “negative models” in biomedical research, where organisms are chosen for their dissimilarity to human physiology. Importantly, the representational scope of Krogh organisms and the generalizability of their characteristics are not fixed or assumed but explored through experimental studies. Research on Krogh organisms is steeped in the comparative method characteristic of zoology and comparative physiology, in which studies of biological variation produce insights into general physiological constraints. Accordingly, we conclude that the Krogh principle exemplifies the advantages of studying biological variation as a strategy to produce generalizable insights

Animals living in polluted environments are a potential source of anti-tumour 2 molecule(s)

Despite advances in in therapeutic interventions and supportive care, the morbidity and mortality associated with cancer has remained significant. Thus there is a need for newer and more powerful anti-tumour agents. The search for new anti-tumour compounds originating from natural resources is a promising research area. Animals living in polluted environments are a potent source of anti-tumour agents. Under polluted milieus, species such as crocodiles, feed on rotten meat, are exposed to heavy metals, endure high levels of radiation, are among the very few species to survive the catastrophic Cretaceous-Tertiary extinction event with a prolonged lifespan. Thus it is reasonable to speculate that animals such as crocodiles have developed mechanisms to defend themselves against cancer. The discovery of antitumor activity in animals such as crocodiles, whales, sharks, etc will stimulate research in finding therapeutic molecules from unusual sources, and has potential for the development of novel antitumor compound(s) that may also overcome current drug resistance. Nevertheless, intensive research in the next few years will be required to realize these expectations

miRNAs Copy Number Variations Repertoire as Hallmark Indicator of Cancer Species Predisposition

Aging is one of the hallmarks of multiple human diseases, including cancer. We hypothesized that variations in the number of copies (CNVs) of specific genes may protect some long-living organisms theoretically more susceptible to tumorigenesis from the onset of cancer. Based on the statistical comparison of gene copy numbers within the genomes of both cancer-prone and -resistant species, we identified novel gene targets linked to tumor predisposition, such as CD52, SAT1 and SUMO. Moreover, considering their genome-wide copy number landscape, we discovered that microRNAs (miRNAs) are among the most significant gene families enriched for cancer progression and predisposition. Through bioinformatics analyses, we identified several alterations in miRNAs copy number patterns, involving miR-221, miR-222, miR-21, miR-372, miR-30b, miR-30d and miR-31, among others. Therefore, our analyses provide the first evidence that an altered miRNAs copy number signature can statistically discriminate species more susceptible to cancer from those that are tumor resistant, paving the way for further investigations.Aging is one of the hallmarks of multiple human diseases, including cancer. We hypothesized that variations in the number of copies (CNVs) of specific genes may protect some long-living organisms theoretically more susceptible to tumorigenesis from the onset of cancer. Based on the statistical comparison of gene copy numbers within the genomes of both cancer-prone and-resistant species, we identified novel gene targets linked to tumor predisposition, such as CD52, SAT1 and SUMO. Moreover, considering their genome-wide copy number landscape, we discovered that microRNAs (miRNAs) are among the most significant gene families enriched for cancer progression and predisposition. Through bioinformatics analyses, we identified several alterations in miRNAs copy number patterns, involving miR-221, miR-222, miR-21, miR-372, miR-30b, miR-30d and miR-31, among others. Therefore, our analyses provide the first evidence that an altered miRNAs copy number signature can statistically discriminate species more susceptible to cancer from those that are tumor resistant, paving the way for further investigations

Probing the protein homeostasis mechanisms in long-lived naked mole-rats

The naked mole-rat (NMR) is a fascinating animal which has unique biological features including eusociality, strict subterranean inhabitation and poikilothermy. It is the longest-living rodent, showing negligible senescence over the majority of its lifespan and high resistance to diseases such as cancer and neurodegeneration. This animal is therefore a compelling system for understanding ageing and age-related diseases. Recent evidence suggests that protein homeostasis (proteostasis) mechanisms may play a vital role in mediating the resistance to multiple forms of stress and diseases and, subsequently, contribute to the exceptional longevity of the NMR. However, this view has been predominately based on protein-level and/or cell viability analyses, and our knowledge is still limited about the modulation of proteotoxic stress responses at the transcriptional level due to a lack of reliable and validated molecular tools. This thesis sets out to develop, optimise and apply new methods to investigate two important and complex proteostatic mechanisms, namely the unfolded protein response (UPR) in the endoplasmic reticulum (ER) and macroautophagy (autophagy), in the NMR. Using these methodologies, the effects of pharmacologically induced in vitro stress and the effects of disease-related neurotoxic protein species on the UPR and autophagy in NMR fibroblasts were investigated. In Chapter 3, RNA-based methods, including an Xbp1 splicing assay and quantitative PCR (RT-qPCR) assays were successfully established to probe the activation and outputs of the UPR in a NMR kidney fibroblast cell line in response to tunicamycin (TU) and thapsigargin (TG)-induced ER stress. In Chapter 4, differences between the UPR of NMR kidney fibroblasts and mouse homologues were identified, where a notably higher threshold of pharmacologically induced UPR activation was observed in the NMR under conditions of mild ER stress. In Chapter 5, LC3B turnover and transcriptional changes of autophagy markers under rapamycin (RA) and chloroquine (CQ)-treated conditions were monitored in an NMR skin fibroblast cell line, where the sensitivity of the NMR skin fibroblasts to CQ, when compared to NMR kidney fibroblasts and mouse NIH3T3 embryonic cells, seemed to be partly attributed to the downregulation of TFEB, a master transcription factor of autophagy. In Chapter 6, the effects of amyloid-beta (Aβ) and α-synuclein oligomers, which are believed to be the major pathogenic species of Alzheimer’s and Parkinson’s diseases, respectively, on the UPR and/or autophagy were investigated in NMR and mouse cells using a combination of molecular and cellular tools. Although no significant changes of UPR markers were observed under Aβ oligomer-treated conditions, the chronic toxicity of wild-type α-synuclein oligomers seemed to be associated with downregulation of genes encoding ER chaperones and autophagy proteins. In Chapter 7, we demonstrate the utility of rational design to create a protein-specific binding probe for the NMR LC3B protein by introducing a peptide derived from a LC3-interacting region (LIR) motif into the inter-repeat loop of a consensus-designed tetratricopeptide repeat protein (CTPR). The results provide proof-of-concept validation of using CTPR-based probes to detect proteins in emerging animal models. Having established a set of reliable methods to investigate the molecular details of the UPR and autophagy in the NMR, we have demonstrated unique features of the NMR, at the transcriptional level, when different forms of in vitro stress are employed. Exploiting these assays to measure the UPR and autophagy, as well as other proteostastic mechanisms, in the NMR under more disease-relevant conditions, may ultimately shed light on therapeutic developments to combat age-related neurodegenerative diseases

The naked mole-rat as an animal model in biomedical research: current perspectives

The naked mole-rat (NMR) is a subterranean rodent that has gained significant attention from the biomedical research community in recent years as molecular mechanisms underlying its unusual biology start to be unraveled. With very low external mortality, NMRs have an unusually long lifespan while showing no signs of aging, such as neurodegeneration or cancer. Furthermore, living underground in large colonies (100 to 300 animals), results in comparatively high carbon dioxide and low oxygen levels, from which NMRs have evolved extreme resistance to both hypoxia and hypercapnia. In this paper we have summarized the latest developments in NMR research and its impact on biomedical research, with the aim of providing a sound background that will inform and inspire further investigations