Aging and proliferative homeostasis: modulation by food restriction in rodents.

In rats fed ad libitum, the fat cell number increases with advancing age; the temporal pattern of this increase differs in the perirenal depot compared with the epididymal depot. Restriction of energy intake reduces the number of fat cells in fat depots whether the restriction is started soon after weaning or in adult life. The capacity for diet to modulate fat cell number is maintained through most, if not all, of the life span. Restriction of energy intake delayed death due to neoplasms; restriction of dietary fat or protein without restriction of energy did not have this action. In the case of leukemia/lymphoma, the data indicated that it was the age of occurrence that was delayed by the restriction of energy intake. Because restriction of dietary energy maintains most physiologic systems in a youthful state and retards a broad spectrum of disease processes, the importance of its effects on cellularity and cell proliferation in its anti-aging action remains to be established.     

Anti-lipoperoxidation action of food restriction

Chronic food restriction inhibited the age-related increase of malondialdehyde production and lipid hydroperoxides in liver mitochondrial and microsomal membranes of ad libitum fed Fischer 344 rats. The anti-lipoperoxidation action of food restriction could not be attributable to the changes in membrane lipid content nor vitamin E status. Restricting calories modified membrane fatty acid composition by increasing linoleic acid and decreasing docosapentaenoic acid content in both membranes. The significance of the fatty acid modification was discussed in terms of anti-lipoperoxidation and membrane fluidity.     

Mechanistic perspectives of calorie restriction on vascular homeostasis

Calorie restriction(CR)is a dietary regime based on low calorie intake.CR without malnutrition extends lifespan in a wide range of organisms from yeast to rodents,and CR can prevent and delay the onset of age-related functional decline and diseases in human and non-human primates.CR is a safe and effective intervention to reduce vascular risk factors in humans.In recent years,studies in rodents have provided mechanistic insights into the beneficial effects of CR on vascular homeostasis,including reduced oxidative stress,enhanced nitric oxide(NO)bioactivity,and decreased inflammation.A number of important molecules,including sirtuins,AMP-activated protein kinase,mammalian targets of rapamycin,endothelial nitric oxidase and their regulatory pathways are involved in the maintenance of vascular homeostasis.Evidence has shown that these pathways are responsible for many aspects of CR’s effects,and that they may also mediate the effects of CR on vasculature.     

Protein oxidation and cellular homeostasis: Emphasis on metabolism

Reactive oxygen species (ROS) are generated as the result of a number of physiological and pathological processes. Once formed ROS can promote multiple forms of oxidative damage, including protein oxidation, and thereby influence the function of a diverse array of cellular processes. This review summarizes the mechanisms by which ROS are generated in a variety of cell types, outlines the mechanisms which control the levels of ROS, and describes specific proteins which are common targets of ROS. Additionally, this review outlines cellular processes which can degrade or repair oxidized proteins, and ultimately describes the potential outcomes of protein oxidation on cellular homeostasis. In particular, this review focuses on the relationship between elevations in protein oxidation and multiple aspects of cellular metabolism. Together, this review describes a potential role for elevated levels of protein oxidation contributing to cellular dysfunction and oxidative stress via impacts on cellular metabolism.     

Autophagy: A critical regulator of cellular metabolism and homeostasis

Plants possess a variety of extracellular leucine-rich repeats receptor-like kinases (LRR-RLKs) to coordinate developmental programs with responses to environmental changes. Out of sixteen families of LRR-RLKs in Arabidopsis, the LRR-RLKII family consists of fourteen individual members, including five Arabidopsis thaliana somatic embryogenesis receptor kinases (AtSERKs). BAK1/AtSERK3 was first identified as a dual co-receptor of BRI1 and FLS2, mediating BR signaling and pathogen-associated molecular pattern (PAMP) triggered immunity (PTI), respectively. Since its identification, many researchers have attempted to elucidate the phosphorylation mechanisms between receptor complexes and identify additional components that interact with receptor complexes to transduce the signaling downstream. Relatively detailed early events in complex formation, phosphorylation sites on the BRI1/BAK1 complex and BAK1-interacting proteins, such as BIK1 and PUB13, have been identified. Small receptor complexes consisting of BAK1 and BIR1 or BAK1 and AtSERK4 regulate cell death during steady state conditions. Moreover, the redundant and distinct functions of AtSERK proteins and other members of the LRR-RLKII family have been revealed. This review focuses on the integration of the information from the most recent studies concerning BAK1 and its homologs.     

Effects of AZT on cellular iron homeostasis

3'-azido-3'-deoxythymidine (AZT), the first chemotherapeutic drug approved by FDA for treatment of HIV-infected patients and still used in combination therapy, has been shown to induce, upon prolonged exposure, severe bone marrow toxicity manifested as anemia, neutropenia and siderosis. These toxic effects are caused by inhibition of heme synthesis and, as a consequence, transferrin receptor (TfR) number appears increased and so iron taken up by cells. Since iron overload can promote the frequency and severity of many infections, siderosis is viewed as a further burden for AIDS patients. We have previously demonstrated that AZT-treated K562 cells showed an increase of the number of TfRs located on the surface of the plasma membrane without affecting their biosynthesis, but slowing down their endocytotic pathway. In spite of the higher number of receptors on the plasma-membrane of AZT-treated cells, intracellular accumulation of iron showed a similar level in control and in drug-exposed cells. The chelating ability of AZT and of its phosphorylated derivatives, both in an acellular system and in K562 cells, was also checked. The results demonstrated that AZT and AZTMP were uneffective as iron chelators, while AZTTP displayed a significant capacity to remove iron from transferrin (Tf). Our results suggest that AZT may be not directly involved in the iron overloading observed upon its prolonged use in AIDS therapy. The iron accumulation found in these patients is instead caused by other unknown mechanisms that need further studies to be clarified.     

The impact of aneuploidy on cellular homeostasis

Genomic instability is a common feature of tumours that has a wide range of disruptive effects on cellular homeostasis. In this review we briefly discuss how instability comes about, then focus on the impact of gain or loss of DNA (aneuploidy) on oxidative stress. We discuss several mechanisms that lead from aneuploidy to the production of reactive oxygen species, including the effects on protein complex stoichiometry, endoplasmic reticulum stress and metabolic disruption. Each of these are involved in positive feedback loops that amplify relatively minor genetic changes into major cellular disruption or cell death, depending on the capacity of the cell to induce antioxidants or processes such as mitophagy that can moderate the disruption. Finally we examine the direct effects of reactive oxygen species on mitosis and how oxidative stress can compromise centrosome number, cytoskeletal integrity and signalling processes that are vital for mitotic fidelity.     

The cellular mechanisms of body iron homeostasis

Cells tightly regulate iron levels through the activity of iron regulatory proteins (IRPs) that bind to RNA motifs called iron responsive elements (IREs). When cells become iron-depleted, IRPs bind to IREs present in the mRNAs of ferritin and the transferrin receptor, resulting in diminished translation of the ferritin mRNA and increased translation of the transferrin receptor mRNA. Similarly, body iron homeostasis is maintained through the control of intestinal iron absorption. Intestinal epithelia cells sense body iron through the basolateral endocytosis of plasma transferrin. Transferrin endocytosis results in enterocytes whose iron content will depend on the iron saturation of plasma transferrin. Cell iron levels, in turn, inversely correlate with intestinal iron absorption. In this study, we examined the relationship between the regulation of intestinal iron absorption and the regulation of intracellular iron levels by Caco-2 cells. We asserted that IRP activity closely correlates with apical iron uptake and transepithelial iron transport. Moreover, overexpression of IRE resulted in a very low labile or reactive iron pool and increased apical to basolateral iron flux. These results show that iron absorption is primarily regulated by the size of the labile iron pool, which in turn is regulated by the IRE/IRP system.     

Selective protection of restriction endonuclease sites

A difficulty that is encountered when attempting to insert a PCR-amplified product or DNA fragment of interest into a particular vector is the presence within the insert of one or more internal restriction endonuclease (RE) sites identical to those selected for the flanks of the insert. Our method circumvents this problem by partially protecting internal RE sites while flanking sites for the same RE are cleaved. The amplified product is first heat denatured in the presence of excess amounts of perfectly complementary oligonucleotides that can anneal to the flanks of the insert. The mixture is allowed to anneal and is subsequently digested with the appropriate endonucleases. This results in the cleavage of the flanking RE sites while digestion at the internal RE site is not efficient. The mixture is subsequently heat denatured and column purified to remove the oligonucleotides. The product is then allowed to anneal and can be used directly in a ligation reaction with the plasmid vector. This method facilitates the construction of recombinant molecules by creating desired flanks while preserving internal RE sites.     

Caloric restriction in mTORC1 control of intestinal homeostasis

Reducing caloric intake, while maintaining adequate nutrition, promotes longevity in diverse organisms, possibly by preserving stem and progenitor cell function. Yilmaz and colleagues (2012) now show that caloric restriction alters intestinal stem cell proliferation and differentiation, and elucidate a mechanism for how the mammalian stem cell niche responds to environmental inputs.     

Functional landscape of SARS-CoV-2 cellular restriction

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Soluble nickel interferes with cellular iron homeostasis

Soluble nickel compounds are likely human carcinogens. The mechanism by which soluble nickel may contribute to carcinogenesis is unclear, though several hypotheses have been proposed. Here we verify the ability of nickel to enter the cell via the divalent metal ion transporter 1 (DMT1) and disturb cellular iron homeostasis. Nickel may interfere with iron at both an extracellular level, by preventing iron from being transported into the cell, and at an intracellular level, by competing for iron sites on enzymes like the prolyl hydroxylases that modify hypoxia inducible factor-1α (HIF-1α). Nickel was able to decrease the binding of the Von Hippel–Lindau (VHL) protein to HIF-1α, indicating a decrease in prolyl hydroxylase activity. The ability of nickel to affect various iron dependent processes may be an important step in nickel dependent carcinogenesis. In addition, understanding the mechanisms by which nickel activates the HIF-1α pathway may lead to new molecular targets in fighting cancer.     

Caveolin-1 and regulation of cellular cholesterol homeostasis

Caveolae are 50- to 100-nm cell surface plasma membrane invaginations present in terminally differentiated cells. They are characterized by the presence of caveolin-1, sphingolipids, and cholesterol. Caveolin-1 is thought to play an important role in the regulation of cellular cholesterol homeostasis, a process that needs to be properly controlled to limit and prevent cholesterol accumulation and eventually atherosclerosis. We have recently generated caveolin-1-deficient [Cav-1(-/-)] mice in which caveolae organelles are completely eliminated from all cell types, except cardiac and skeletal muscle. In the present study, we examined the metabolism of cholesterol in wild-type (WT) and Cav-1(-/-) mouse embryonic fibroblasts (MEFs) and mouse peritoneal macrophages (MPMs). We observed that Cav-1(-/-) MEFs are enriched in esterified cholesterol but depleted of free cholesterol compared with their wild-type counterparts. Similarly, Cav-1(-/-) MPMs also contained less free cholesterol and were enriched in esterified cholesterol on cholesterol loading. In agreement with this finding, caveolin-1 deficiency was associated with reduced free cholesterol synthesis but increased acyl-CoA:cholesterol acyl-transferase (ACAT) activity. In wild-type MPMs, we observed that caveolin-1 was markedly upregulated on cholesterol loading. Despite these differences, cellular cholesterol efflux from MEFs and MPMs to HDL was not affected in the Cav-1-deficient cells. Neither ATP-binding cassette transporter G1 (ABCG1)- nor scavenger receptor class B type I (SR-BI)-mediated cholesterol efflux was affected. Cellular cholesterol efflux to apolipoprotein A-I was not significantly reduced in Cav-1(-/-) MPMs compared with wild-type MPMs. However, ABCA1-mediated cholesterol efflux was clearly more sensitive to the inhibitory effects of glyburide in Cav-1(-/-) MPMs versus WT MPMs. Taken together, these findings suggest that caveolin-1 plays an important role in the regulation of intracellular cholesterol homeostasis and can modulate the activity of other proteins that are involved in the regulation of intracellular cholesterol homeostasis.     

In the beginning, there was the cell: cellular homeostasis

In the past 5 years, the biomedical, scientific community has sequenced the genomes of several organisms (including Homo sapiens), has cloned entire organisms and has determine the molecular structures for several membrane proteins. These advances combined with the advances in technology enabling high-throughput drug screening, gene expression readout using DNA chips and evolving proteomic techniques, make it imperative that physiologist and biomedical professionals understand the basis of cellular function and homeostasis. The Cellular Homeostasis Refresher Course at Experimental Biology 2004 in Washington, DC, was designed to fulfill this need. The specific topics covered were 1) generation of membrane potential, 2) an update on cellular mechanisms of ion homeostasis, channels and transporters, and 3) cellular volume homeostasis, and regulation of intracellular pH.