Peak Waste: When Is It Likely to Occur?

Population and per capita gross domestic product (GDP) projections are used to estimate total global municipal solid waste (MSW) generation over the twenty‐first century. Some projections for global population suggest that it will peak this century. Waste generation rates per capita generally increase with affluence, although in the most affluent countries there is also a trend toward dematerialization. The confluence of these factors means that at some point in the future total global waste generation could possibly peak. To determine when peak waste might occur, we used the shared‐socioeconomic pathway scenarios (used in Intergovernmental Panel on Climate Change [IPCC] studies) combined with estimates of municipal solid waste (MSW) generation rates, extrapolated from our work for the World Bank. Despite the expectation that total MSW generation in Organisation for Economic Co‐operation and Development (OECD) and high‐income countries will peak mid‐century, with current trajectories global peak waste is not expected before 2100. The peak could be moved forward to around 2075 and reduced in intensity by some 30% if a more aggressive sustainability growth scenario were followed, rather than the current business‐as‐usual scenario. Further, the magnitude of peak waste is sensitive to the intensity of waste generation; it could vary from 7.3 to 10.9 megatonnes per day under the sustainability scenario. The timing of peak waste will substantially depend on the development of cities in Sub‐Saharan Africa, where population growth rates are more than double the rest of the world.     

IL-2-engineered nano-APC effectively activates viral antigen-mediated T cell responses from chronic hepatitis B virus-infected patients

Impaired function of virus-specific T cells resulting from virus persistence is one of the major mechanisms underlying the development of chronic hepatitis B viral infection. Previously, we found that IL-2 can restore the effector function of T cells rendered tolerant by Ag persistence. However, systemic administration of IL-2 induces organ pathology and expansion of T regulatory cells. In this study, we show that nano-APC with engineered HLA alleles and IL-2 deliver peptide-MHC complexes, costimulatory molecules, and IL-2 to Ag-responding T cells, resulting in enhanced expression of CD25 and activation of TCR signaling pathways, while suppressing PD-1 expression on viral-responding CD8 T cells from chronic hepatitis B virus patients. The enhanced activation of CD4 and CD8 T cells induced by IL-2-nano-APC was Ag dependent and IL-2-nano-APC did not affect T regulatory cells. At a size of 500 nm, the nano-APC effectively induce immune synapse formation on Ag-specific T cells and accumulate as free particles in the lymphoid organs. These attributes of IL-2-nano-APC or other bioadjuvant-engineered nano-APC have profound implications for their use as a therapeutic strategy in the treatment of chronic hepatitis B virus infection or other chronic viral diseases.     

Intestine-specific expression of Apobec-1 rescues apolipoprotein B RNA editing and alters chylomicron production in Apobec1−/− mice

Intestinal apolipoprotein B (apoB) mRNA undergoes C-to-U editing, mediated by the catalytic deaminase apobec-1, which results in translation of apoB48. Apobec1^−/− mice produce only apoB100 and secrete larger chylomicron particles than those observed in wild-type (WT) mice. Here we show that transgenic rescue of intestinal apobec-1 expression (Apobec1^Int/O) restores C-to-U RNA editing of apoB mRNA in vivo, including the canonical site at position 6666 and also at approximately 20 other newly identified downstream sites present in WT mice. The small intestine of Apobec1^Int/O mice produces only apoB48, and the liver produces only apoB100. Serum chylomicron particles were smaller in Apobec1^Int/O mice compared with those from Apobec1^−/− mice, and the predominant fraction of serum apoB48 in Apobec1^Int/O mice migrated in lipoproteins smaller than chylomicrons, even when these mice were fed a high-fat diet. Because apoB48 arises exclusively from the intestine in Apobec1^Int/O mice and intestinal apoB48 synthesis and secretion rates were comparable to WT mice, we were able to infer the major sites of origin of serum apoB48 in WT mice. Our findings imply that less than 25% of serum apoB48 in WT mice arises from the intestine, with the majority originating from the liver.     

Discovery of XL888: A novel tropane-derived small molecule inhibitor of HSP90

With structural guidance, tropane-derived HTS hits were modified to optimize for HSP90 inhibition and a desirable in vivo profile. Through an iterative SAR development process 12i (XL888) was discovered and shown to reduce HSP90 client protein content in PD studies. Furthermore, efficacy experiments performed in a NCI-N87 mouse xenograft model demonstrated tumor regression in some dosing regimens.     

Structure based design of iminohydantoin BACE1 inhibitors: identification of an orally available, centrally active BACE1 inhibitor

From an initial lead 1, a structure-based design approach led to identification of a novel, high-affinity iminohydantoin BACE1 inhibitor that lowers CNS-derived Aβ following oral administration to rats. Herein we report SAR development in the S3 and F' subsites of BACE1 for this series, the synthetic approaches employed in this effort, and in vivo data for the optimized compound.     

Will the real aging Sirtuin please stand up?

Initial studies linking Sirtuins to longevity in yeast initiated what is now a rich vein of aging research that is full of promise and fraught with controversy. Missing was a demonstration that enhanced Sirtuin expression extends lifespan in mammals. Now Kanfi et al. provide the evidence but with an interesting plot twist – the lesser known SIRT6 is the longevity factor.While Sirtuins, a highly conserved class of protein deacetylases, have been linked to longevity in a variety of model organisms and are among the most studied proteins in the context of aging, their role remains controversial. Increased expression of the founding member of the class, yeast SIR2, was reported to extend replicative lifespan over a decade ago and this was followed by reports that overexpression of SIR2 orthologs leads to enhanced longevity in worms and flies ^{1, 2}. More recent reports have called the worm and fly data into question ^{3, 4} and while increased Sir2 activity may enhance longevity under certain conditions in all three organisms, mechanistic studies have not converged on a specific activity coupled to aging.Seven mammalian Sir2 homologs (SIRT1-SIRT7) have been identified. A myriad of activities in a range of mammalian tissues have been attributed to SIRT1, a protein most structurally related to yeast Sir2, often linked to protection from the onset of chronic disease states. Yet transgenic mice with increased SIRT1 expression are not long-lived ⁵, further adding to what is becoming a great science mystery. Until recently, while SIRT1 was being intensely studied, the other Sirtuins were mostly waiting in the wings. In the last few years, however, many of them have been linked to interesting biological functions and, with the recent report by Kanfi et al. ⁶, SIRT6 assumes a central role in aging.The primary finding of Kanfi et al. is that transgenic mice overexpressing SIRT6 have enhanced longevity, but only in males ⁶. While the longevity enhancement is modest (15% increase in median lifespan), the data is rigorous. Similar effects were seen in two different founder transgenic lines, large numbers of mice were included in the study and a mixed genetic background was selected for the study with equal contribution of two long-lived inbred backgrounds. The authors also attempted to address whether the longevity benefit results from retarded aging, as opposed to protection from cancer, a common cause of mortality in mice. While a challenging issue to resolve in a single study, tantalizing evidence is provided that SIRT6 is indeed a modulator of aging. For instance, if longevity is enhanced simply by eliminating the most common type of cancer, lung in these mice, then a post-mortem analysis would yield a skewing of the tumor spectrum. Yet no significant differences were seen in the incidence of different tumors. Moreover, other age-related pathologies were evident in equal proportion. These findings are consistent with a model whereby the aging process is delayed, with animals developing and succumbing to the same diseases later in life (Figure 1). Coupled with earlier findings that SIRT6 overexpression in mice (1) leads to protection from diet-induced obesity and (2) suppresses expression of NF-κB-dependent inflammatory markers, and moreover that SIRT6 expression is induced by caloric restriction in rats, it is fair to say that the deacetylase has certainly entered the realm of top-tier candidate modulatory factors of aging.Open in a separate windowFigure 1SIRT6 expression and longevity. Decreased SIRT6 expression leads to genome instability, as well as progeroid phenotypes that resemble accelerated aging. In contrast, increased SIRT6 expression alters cell and physiological phenotypes in a manner that promotes enhanced longevity.Long debated is whether mouse or human models of progeria, diseases with a rapid onset of a subset of aging pathologies, are truly accelerated aging syndromes ⁷. One argument against this hypothesis was that the genetic interventions giving rise to progeroid syndromes are non-overlapping with those linked to enhanced longevity. This disconnect is starting to dissolve as genes that go both ways are being identified. p53 is arguably the first example; constitutive p53 activation induces progeria phenotypes ⁸, whereas enhanced p53 activity under normal regulatory control leads to lifespan extension ⁹. With the study by Kanfi et al. ⁶, SIRT6 emerges as a new member of this short list of genes since it was previously shown that SIRT6^−/− mice have metabolic defects and rapidly present with abnormalities often associated with aging, such as kyphosis and loss of subcutaneous fat ¹⁰. Thus, reduced SIRT6 expression may accelerate aspects of aging whereas enhanced SIRT6 expression may delay them.A primary question is why increased SIRT6 expression enhances longevity, and several models are possible in addition to regulation of NF-κB. First are the metabolic consequences of enhanced SIRT6 activity, which are further elaborated in Kanfi et al. by examination of metabolic changes during aging of mice on a normal ad lib diet ⁶. First, Sirt6-transgenic mice are able to maintain healthy glucose metabolism later in life than controls, a feature often associated with longevity. However, both males and females maintain better metabolic function, therefore, this finding, while it may be linked, is separable from the dimorphic effects on lifespan. A further clue comes from the finding that IGF-1 levels are reduced in serum of male but not female overexpressing SIRT6 and that this is coupled to a corresponding increase in IGFBP-1 levels. Interestingly, these changes place the males in line with the females with regard to both factors. The downstream consequences of reduced IGF-1 levels are most apparent in white adipose tissue, which show significant reductions in AKT phosphorylation again only in males. Metabolic changes in fat tissue are increasingly linked to lifespan. These findings raise the intriguing possibility that the enhanced longevity in male Sirt6-transgenic mice occur because they have metabolic profiles more like that of females.Whole-genome microarray analysis of liver tissue from mice overexpressing SIRT6 raises another intriguing possible mechanism linked to metabolism. First, the biggest gene expression changes were apparent in male transgenic livers and, importantly, many of the observed differences overlap with those of calorie-restricted mice. Since those mice also have reduced serum IGF-1 and increased IGFBP-1 levels ¹¹, gene expression changes could be cause or consequence of changes to the endocrine axis. Moreover, these findings support the hypothesis that SIRT6 overexpression phenocopies aspects of calorie restriction in males. Another possibility that Sirt6-transgenic mice eat less, mimicking calorie restriction in a more direct fashion, can be largely discounted since an early study reported equal food consumption ¹².While SIRT1 is relatively promiscuous in its choice of substrate for deacetylation, finding targets for SIRT6 proved a more challenging endeavor. Recently, however, the identification of histone H3K9 and K56 may explain roles identified for SIRT6 in the DNA damage response and in telomere maintenance ^{13, 14}. Cells from SIRT6^−/− mice experience a dramatic elevation in genome instability indicative of defective double strand break (DSB) repair ¹⁰ and by contrast, enhanced SIRT6 activity stimulates DSB repair, particularly in response to oxidative stress ¹⁵. Deacetylation of H3K56 is linked to enhanced DNA repair, as is mono-ADP ribosylation of PARP, an alternate NAD⁺-dependent enzymatic activity of SIRT6. SIRT6 also associates with telomere heterochromatin, where it deacetylates both H3K9 and H3K56 ^{13, 16}. Reduced SIRT6 expression in primary fibroblasts leads to a range of replication-dependent defects in telomere maintenance, promoting premature senescence. Functions of SIRT6 either at sites of DSBs or at telomeres could underlie both progeroid and/or enhanced longevity phenotypes.While SIRT1 resembles yeast Sir2 from a structural perspective, it may be SIRT6 that is a closer functional ortholog. In their respective organisms, expression levels of each correlate with longevity. Moreover, both are most closely linked with histone deacetylation and have roles in genome maintenance both at telomeres and in response to DNA damage. Both also may link genome maintenance to nutrient and stress conditions in the cell. A challenge moving ahead will be to link SIRT6 enzymatic functions and cellular properties to the metabolic and longevity phenotypes apparent in the transgenic and knockout mice.The studies of Kanfi et al. place SIRT6 in a group of genes that when genetically modified can lead to enhanced mammalian longevity. However, they do not rule out roles for other Sirtuins in aging. For instance, while whole body overexpression of SIRT1 appears not to enhance lifespan, given the range of its functions in different tissues, more informative may be the lifespan phenotypes of mice overexpressing SIRT1 in specific tissues. In addition, little is known about other Sirtuins and given interesting metabolic roles especially for those localized to the mitochondria, it would not be surprising if they affect aging as well ². The role of Sirtuins in aging remains controversial and undoubtedly twists and turns are yet to come, but the report by Kanfi et al. makes the case for Sirtuins and aging far more compelling, at least in the case of SIRT6.     

Scaling up: examining the macroecology of ectomycorrhizal fungi

Ectomycorrhizal (ECM) fungi play major ecological roles in temperate and tropical ecosystems. Although the richness of ECM fungal communities and the factors controlling their structure have been documented at local spatial scales, how they vary at larger spatial scales remains unclear. In this issue of Molecular Ecology, Tedersoo et al. (2012) present the results of a meta‐analysis of ECM fungal community structure that sheds important new light on global‐scale patterns. Using data from 69 study systems and 6021 fungal species, the researchers found that ECM fungal richness does not fit the classic latitudinal diversity gradient in which species richness peaks at lower latitudes. Instead, richness of ECM fungal communities has a unimodal relationship with latitude that peaks in temperate zones. Intriguingly, this conclusion suggests the mechanisms driving ECM fungal community richness may differ from those of many other organisms, including their plant hosts. Future research will be key to determine the robustness of this pattern and to examine the processes that generate and maintain global‐scale gradients of ECM fungal richness.     

Residues distant from the active site influence protein-tyrosine phosphatase 1B inhibitor binding

Regions of protein-tyrosine phosphatase (PTP) 1B that are distant from the active site yet affect inhibitor binding were identified by a novel library screen. This screen was based on the observation that expression of v-Src in yeast leads to lethality, which can be rescued by the coexpression of PTP1B. However, this rescue is lost when yeast are grown in the presence of PTP1B inhibitors. To identify regions of PTP1B (amino acids 1-400, catalytic domain plus 80-amino acid C-terminal tail) that can affect the binding of the difluoromethyl phosphonate (DFMP) inhibitor 7-bromo-6-difluoromethylphosphonate 3-naphthalenenitrile, a library coexpressing PTP1B mutants and v-Src was generated, and the ability of yeast to grow in the presence of the inhibitor was evaluated. PTP1B inhibitor-resistant mutations were found to concentrate on helix alpha7 and its surrounding region, but not in the active site. No resistant amino acid substitutions were found to occur in the C-terminal tail, suggesting that this region has little effect on active-site inhibitor binding. An in-depth characterization of a resistant substitution localizing to region alpha7 (S295F) revealed that this change minimally affected enzyme catalytic activity, but significantly reduced the potency of a panel of structurally diverse DFMP PTP1B inhibitors. This loss of inhibitor potency was found to be due to the difluoro moiety of these inhibitors because only the difluoro inhibitors were shifted. For example, the inhibitor potency of a monofluorinated or non-fluorinated analog of one of these DFMP inhibitors was only minimally affected. Using this type of library screen, which can scan the nearly full-length PTP1B sequence (catalytic domain and C-terminal tail) for effects on inhibitor binding, we have been able to identify novel regions of PTP1B that specifically affect the binding of DFMP inhibitors.     

Cytoplasmic targeting motifs control localization of toll-like receptor 9

Toll-like receptors (TLRs) are essential for host defense. Although several TLRs reside on the cell surface, nucleic acid recognition of TLRs occurs intracellularly. For example, the receptor for CpG containing bacterial and viral DNA, TLR9, is retained in the endoplasmic reticulum. Recent evidence suggests that the localization of TLR9 is critical for appropriate ligand recognition. Here we have defined which structural features of the TLR9 molecule control its intracellular localization. Both the cytoplasmic and ectodomains of TLR9 contain sufficient information, whereas the transmembrane domain plays no role in intracellular localization. We identify a 14-amino acid stretch that directs TLR9 intracellularly and confers intracellular localization to the normally cell surface-expressed TLR4. Truncation or mutation of the cytoplasmic tail of TLR9 reveals a vesicle localization motif that targets early endosomes. We propose a model whereby modification of the cytoplasmic tail of TLR9 results in trafficking to early endosomes where it encounters CpG DNA.