Organismal Aging and Oxidants beyond Macromolecules Damage

The relationship between oxidants and organismal aging was first articulated through the free radical theory of aging. One of the major predictions of the free radical theory of aging is that oxidative stress shortens organisms’ lifespan because of an increased level of oxidants, which are damaging to macromolecules. However, challenging the role of oxidants in age‐related diseases, there is now sufficient evidence that antioxidant supplements do not provide significant health benefits. Interestingly, in addition to an increase in oxidant‐mediated macromolecules damage, there is convincing experimental data to support the role of senescent cells in the process of aging. Here, the current knowledge regarding the role of oxidants and cellular senescence in organismal aging is reviewed and it is proposed that, in addition to the role of oxidants as inducers of macromolecular damage, oxidants may also function as regulators of signaling pathways involved in the establishment of cellular senescence. If this role for oxidants is established, it may be necessary to modify the free radical theory of aging from “Organisms age because cells accumulate reactive oxygen species‐dependent damage over time” to: “Organisms age because cells accumulate oxidants’‐dependent damage and oxidants’‐dependent senescent characteristics over time.”     

Effects of an artificial hay aroma and compound feed formulation on feed intake pattern,rumen function and milk production in lactating dairy cows

The Kempen system is a dairy feeding system in which diet is provided in the form of a compound feed (CF) and hay offered ad libitum. Ad libitum access to CF and hay allows cows in this system to achieve a high DM intake (DMI). Out of physiological concerns, the voluntary hay intake could be increased and the consumption pattern of CF could be manipulated to maintain proper rumen functioning and health. This study investigated the effects of an artificial hay aroma and CF formulation on feed intake pattern, rumen function and milk production in mid- to late-lactating dairy cows. Twenty Holstein–Friesian cows were assigned to four treatments in a 4 × 4 Latin square design. Diet consisted of CF and grass hay (GH), fed separately, and both offered ad libitum, although CF supply was restricted in maximum meal size and speed of supply by an electronic system. Treatments were the combination of two CF formulations – high in starch (CHS) and fibre (CHF); and two GH – untreated (UGH) and the same hay treated with an artificial aroma (TGH). Meal criteria were determined using three-population Gaussian–Gaussian–Weibull density functions. No GH × CF interaction effects on feed intake pattern characteristics were found. Total DMI and CF intake, but not GH intake, were greater (P < 0.01) in TGH treatment, and feed intake was not affected by type of CF. Total visits to feeders per day, visits to the GH feeder, visits to the CF feeder and CF eating time (all P < 0.01) were significantly greater in cows fed with TGH. Meal frequency, meal size and meal duration were unaffected by treatments. Cows fed CHF had a greater milk fat (P = 0.02), milk urea content (P < 0.01) and a greater milk fat yield (P < 0.01). Cows fed TGH had a greater milk lactose content and lactose yield (P < 0.05), and milk urea content (P < 0.01). Cows fed TGH had smaller molar proportions of acetic acid and greater molar proportions of propionic acid compared with UGH. In conclusion, treatment of GH with an artificial aroma increased CF intake and total DMI, but did not affect hay intake. Additionally, GH treatment increased the frequency of visits to both feeders, and affected rumen volatile fatty acid profile. Type of CF did not affect meal patterns, ruminal pH, nor fermentation profiles.     

Hepatoprotective effect of pyrroloquinoline quinone against alcoholic liver injury through activating Nrf2-mediated antioxidant and inhibiting TLR4-mediated inflammation responses

The present study was aimed at investigating the hepatoprotective effect of pyrroloquinoline quinone (PQQ) against acute alcoholic liver injury in mice. Acute alcoholic liver injury model was established in mice, and they were administrated with PQQ to investigate its hepatoprotective effect. Our results shows that PQQ can significantly ameliorate acute alcoholic liver injury by decreasing the hepatic marker enzymes, including serum alanine transaminase (ALT) and aspartate transaminase (AST), and increasing the levels of alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) in the liver. And PQQ can also significantly reduce the content of hepatic triglyceride (TG) and malondialdehyde (MDA). Moreover, PQQ attenuated alcohol-induced oxidative damage by activating NF-E2-related factor 2 (Nrf2)-mediated signaling pathway, and inhibiting Toll-like receptor 4 (TLR4)-mediated nuclear factor-kappa B (NF-κB) signaling pathway. Our findings have elucidated the liver protection mechanism of PQQ, which would encourage the further exploitation of PQQ as a hepatoprotective functional food.     

Dissecting the roles of Cse1 and Nup2 in classical NLS‐cargo release in vivo

The importin α/β transport machinery mediates the nuclear import of cargo proteins that bear a classical nuclear localization sequence (cNLS). These cargo proteins are linked to the major nuclear protein import factor, importin‐β, by the importin‐α adapter, after which cargo/carrier complexes enter the nucleus through nuclear pores. In the nucleus, cargo is released by the action of RanGTP and the nuclear pore protein Nup2, after which the importins are recycled to the cytoplasm for further transport cycles. The nuclear export of importin‐α is mediated by Cse1/CAS. Here, we exploit structures of functionally important complexes to identify residues that are critical for these interactions and provide insight into how cycles of protein import and recycling of importin‐α occur in vivo using a Saccharomyces cerevisiae model. We examine how these molecular interactions impact protein localization, cargo import, function and complex formation. We show that reversing the charge of key residues in importin‐α (Arg44) or Cse1 (Asp220) results in loss of function of the respective proteins and impairs complex formation both in vitro and in vivo. To extend these results, we show that basic residues in the Nup2 N‐terminus are required for both Nup2 interaction with importin‐α and Nup2 function. These results provide a more comprehensive mechanistic model of how Cse1, RanGTP and Nup2 function in concert to mediate cNLS‐cargo release in the nucleus.     

PagR mediates the precise regulation of Salmonella pathogenicity island 2 gene expression in response to magnesium and phosphate signals in Salmonella Typhimurium

To establish systemic infections, Salmonella enterica serovar Typhimurium (S. Typhimurium) requires Salmonella pathogenicity island 2 (SPI‐2) to survive and replicate within macrophages. High expression of many SPI‐2 genes during the entire intracellular growth period within macrophages is essential, as it contributes to the formation of Salmonella‐containing vacuole and bacterial replication. However, the regulatory mechanisms underlying the sustained induction of SPI‐2 within macrophages are not fully understood. Here, we revealed a time‐dependent regulation of SPI‐2 expression mediated by a novel regulator PagR (STM2345) in response to the low Mg²⁺ and low phosphate (P_i) signals, which ensured the high induction of SPI‐2 during the entire intramacrophage growth period. Deletion of pagR results in reduced bacterial replication in macrophages and attenuation of systemic virulence in mice. The effects of pagR on virulence are dependent on upregulating the expression of slyA, a regulator of SPI‐2. At the early (0–4 hr) and later (after 4 hr) stage post‐infection of macrophages, pagR is induced by the low P_i via PhoB/R two‐component systems and low Mg²⁺ via PhoP/Q systems, respectively. Collectively, our findings revealed that the PagR‐mediated regulatory mechanism contributes to the precise and sustained activation of SPI‐2 genes within macrophages, which is essential for S. Typhimurium systemic virulence.     

Are offspring begging levels exaggerated beyond the parental optimum? Evidence from a bidirectional selection experiment

Parental care involves elaborate behavioural interactions between parents and their offspring, with offspring stimulating their parents via begging to provision resources. Thus, begging has direct fitness benefits as it enhances offspring growth and survival. It is nevertheless subject to a complex evolutionary trajectory, because begging may serve as a means for the offspring to manipulate parents in the context of evolutionary conflicts of interest. Furthermore, it has been hypothesized that begging is coadapted and potentially genetically correlated with parental care traits as a result of social selection. Further experiments on the causal processes that shape the evolution of begging are therefore essential. We applied bidirectional artificial selection on begging behaviour, using canaries (Serinus canaria) as a model species. We measured the response to selection, the consequences for offspring development, changes in parental care traits, here the rate of parental provisioning, as well as the effects on reproductive success. After three generations of selection, offspring differed in begging behaviour according to our artificial selection regime: nestlings of the high begging line begged significantly more than nestlings of the low begging line. Intriguingly, begging less benefitted the nestlings, as reflected by on average significantly higher growth rates, and increased reproductive success in terms of a higher number of fledglings in the low selected line. Begging could thus represent an exaggerated trait, possibly because parent–offspring conflict enhanced the selection on begging. We did not find evidence that we co‐selected on parental provisioning, which may be due to the lack of power, but may also suggest that the evolution of begging is probably not constrained by a genetic correlation between parental provisioning and offspring begging.     

Oligomerization of RIG‐I and MDA5 2CARD domains

The innate immune system is the first line of defense against invading pathogens. The retinoic acid‐inducible gene I (RIG‐I) like receptors (RLRs), RIG‐I and melanoma differentiation‐associated protein 5 (MDA5), are critical for host recognition of viral RNAs. These receptors contain a pair of N‐terminal tandem caspase activation and recruitment domains (2CARD), an SF2 helicase core domain, and a C‐terminal regulatory domain. Upon RLR activation, 2CARD associates with the CARD domain of MAVS, leading to the oligomerization of MAVS, downstream signaling and interferon induction. Unanchored K63‐linked polyubiquitin chains (polyUb) interacts with the 2CARD domain, and in the case of RIG‐I, induce tetramer formation. However, the nature of the MDA5 2CARD signaling complex is not known. We have used sedimentation velocity analytical ultracentrifugation to compare MDA5 2CARD and RIG‐I 2CARD binding to polyUb and to characterize the assembly of MDA5 2CARD oligomers in the absence of polyUb. Multi‐signal sedimentation velocity analysis indicates that Ub₄ binds to RIG‐I 2CARD with a 3:4 stoichiometry and cooperatively induces formation of an RIG‐I 2CARD tetramer. In contrast, Ub₄ and Ub₇ interact with MDA5 2CARD weakly and form complexes with 1:1 and 2:1 stoichiometries but do not induce 2CARD oligomerization. In the absence of polyUb, MDA5 2CARD self‐associates to forms large oligomers in a concentration‐dependent manner. Thus, RIG‐I and MDA5 2CARD assembly processes are distinct. MDA5 2CARD concentration‐dependent self‐association, rather than polyUb binding, drives oligomerization and MDA5 2CARD forms oligomers larger than tetramer. We propose a mechanism where MDA5 2CARD oligomers, rather than a stable tetramer, function to nucleate MAVS polymerization.     

Protein kinases phosphorylate long disordered regions in intrinsically disordered proteins

Phosphorylation is a major post‐translational modification that plays a central role in signaling pathways. Protein kinases phosphorylate substrates (phosphoproteins) by adding phosphate at Ser/Thr or Tyr residues (phosphosites). A large amount of data identifying and describing phosphosites in phosphoproteins has been reported but the specificity of phosphorylation is not fully resolved. In this report, data of kinase‐substrate pairs identified by the Kinase‐Interacting Substrate Screening (KISS) method were used to analyze phosphosites in intrinsically disordered regions (IDRs) of intrinsically disordered proteins. We compared phosphorylated and nonphosphorylated IDRs and found that the phosphorylated IDRs were significantly longer than nonphosphorylated IDRs. The phosphorylated IDR is often the longest IDR (71%) in a phosphoprotein when only a single phosphosite exists in the IDR, and when the phosphoprotein has multiple phosphosites in an IDR(s), the phosphosites are primarily localized in a single IDR (78%) and this IDR is usually the longest one (81%). We constructed a stochastic model of phosphorylation to estimate the effect of IDR length. The model that accounted for IDR length produced more realistic results when compared with a model that excluded the IDR length. We propose that the IDR length is a significant determinant for locating kinase phosphorylation sites in phosphoproteins.