Biology subjects

Singh, B. K.

Publications and source records attributed to Singh, B. K..

25 records · Page 2Linked to original sources

bioRxiv2020

Development of an in vitro senescent hepatic cell model for metabolic studies in aging

Although aging in the liver contributes to the development of chronic liver diseases such as NAFLD and insulin resistance, little known about the molecular and metabolic details of aging in hepatic cells. To examine these issues, we used sequential oxidative stress with hydrogen peroxide to induce premature senescence in AML12 hepatic cells. The senescent cells exhibited molecular and metabolic signatures, increased SA-{beta}Gal and {gamma}H2A.X staining, and elevated senescence and pro-inflammatory gene expression that resembled livers from aged mice. Metabolic phenotyping showed fuel switching towards glycolysis and mitochondrial glutamine oxidation as well as impaired energy production. The senescent AML12 cells also had increased mTOR signaling and decreased autophagy which likely contributed to the fuel switching from {beta}-oxidation that occurred in normal AML12 cells. Additionally, senescence activated secretory proteins from conditioned media of senescent cells sensitized normal AML12 cells to palmitate-induced toxicity, a known pathological effect of hepatic aging. In summary, we have generated senescent AML12 cells which displayed the molecular hallmarks of aging, and also exhibited the aberrant metabolic phenotype, mitochondrial function, and cell signaling that occur in the aged liver.

cell biology↗

bioRxiv2020

Autocrine IL11 cis-signaling in hepatocytes is an initiating nexus between lipotoxicity and non-alcoholic steatohepatitis

Background and aimsIL11 signaling is important in non-alcoholic steatohepatitis (NASH) but how it contributes to NASH pathologies beyond fibrosis is not known. Here we investigate the role of IL11 signaling in hepatocyte lipotoxicity. MethodsHepatocytes were stimulated with IL6, IL11, HyperIL6, or HyperIL11 alone or in the presence of soluble gp130 (sgp130) or soluble IL11RA (sIL11RA), or loaded with palmitate in the presence of IgG or anti-IL11RA (X209) antibodies or sgp130. Effects were assessed using colorimetric ALT, GSH, or ELISA assays, immunoblots, and flow cytometry. The relative contributions of IL11 cis-versus -trans signaling in vivo was assessed in two preclinical NASH models using a high fat methionine/choline deficient diet or a Western diet with liquid fructose in C57BL6/Ntac mice injected with AAV8-Alb-Cre, AAV8-Alb-sgp130, in mice with hepatocyte-specific deletion of Il11ra (CKO), and in mice with global deletion of Il11ra injected with AAV8-Alb-mIl11ra or AAV8-Alb-sIl11ra. Livers and serum were collected; serum samples were analyzed using biochemistry and liver tissues were analyzed by histology, qPCR, immunobloting, hydroxyproline, and GSH assays. ResultsWe show that lipid-laden hepatocytes secrete IL11, which acts via autocrine cis-signaling to cause lipoapoptosis. IL11 causes lipotoxic hepatocyte death through activation of non-canonical signaling pathways and increased NOX4-derived reactive oxygen species. In two preclinical models, hepatocyte-specific deletion of Il11ra1 protects mice from all aspects of NASH with beneficial effects on body weight. In accordance, restoration of IL11 cis-signaling in hepatocytes only in mice globally deleted for Il11ra1 reconstitutes steatosis and inflammation. Throughout, we found no evidence to support the existence of IL6 or IL11 trans-signaling in the liver. ConclusionWe conclude that autocrine IL11-mediated cell death underlies hepatocyte lipotoxicity and that liver fibrosis and inflammation occur subsequently. These data highlight a new disease mechanism for the transition from compensated fatty liver disease to NASH.

molecular biology↗

bioRxiv2019

Redefining Interleukin 11 as a regeneration-limiting hepatotoxin

Acetaminophen (APAP) overdose is a leading cause of untreatable liver failure. In the mouse model of APAP-induced liver injury (AILI), the administration of recombinant human interleukin 11 (rhIL11) is protective. Here we show that the beneficial effect of rhIL11 in the mouse is due to its unexpected and paradoxical inhibition of endogenous mouse IL11 activity. Contrary to the accepted paradigm IL11 is a potent hepatotoxin across species, which is secreted from damaged hepatocytes to drive an autocrine loop of NOX4 and JNK-dependent apoptosis. Mice with hepatocyte-specific Il11 expression spontaneously develop liver failure whereas those with Il11ra1 deletion are remarkably protected from AILI. Neutralizing anti-IL11R antibodies administered to moribund mice 10 hours following a lethal APAP overdose results in 90% survival that is associated with very large liver regeneration. Our data overturn a misconception, identify a new disease mechanism and suggest IL11 as a therapeutic target for liver regeneration.

physiology↗

bioRxiv2019

Predicting lymphatic filariasis elimination in data-limited settings: a reconstructive computational framework for combining data generation and model discovery

Although there is increasing recognition of the importance of mathematical models in the effective design and management of long-term parasite elimination, it is also becoming clear that to be most useful parasite transmission models must accurately reflect the processes pertaining to local infection dynamics. These models must also be identified even when the data required for characterizing the local transmission process are limited or incomplete, as is often the case for neglected tropical diseases, including the disease system studied in this work, viz. lymphatic filariasis (LF). Here, we draw on progress made in the field of computational knowledge discovery to present a reconstructive simulation framework that addresses these challenges by facilitating the discovery of data and models concurrently in order to deliver reliable location-specific predictions pertaining to LF elimination in areas where we have insufficient observational data. Using available data from eight sites from Nigeria and elsewhere, we demonstrate that our data-model discovery system is able to identify local transmission models using a generalized knowledge of filarial transmission dynamics, monitoring survey data, and details of historical interventions, which in turn can also generate information regarding the pre-control endemic status of LF in each study site. Forecasts of the impacts of interventions made by the models discovered using the reconstructed baseline data not only matched temporal infection observations, but also provided critical information regarding when transmission interruption is likely to have occurred. Assessments of elimination and recrudescence probabilities based on these models also suggested a protective effect of vector control against the reemergence of transmission after stopping drug treatments. The reconstructive computational framework for model and data discovery developed here highlights how coupling models with available data can generate new knowledge about complex, data-limited systems, and ultimately support the effective management of disease programs in the face of critical data gaps.\n\nAuthor summaryAs modelling becomes commonly used in the design and evaluation of parasite elimination programs, the need for well-defined models and datasets describing the nature of transmission processes in endemic settings is becoming pronounced. For many neglected tropical diseases, including the disease investigated in this study, lymphatic filariasis (LF), however, data for model identification are typically sparse or incomplete. In this study, we present a new data-model computational discovery system that couples data-assimilation methods based on existing monitoring survey data with model-generated data about baseline conditions, in order to discover the local LF transmission models required for simulating the impacts of interventions for achieving parasite elimination in typical endemic locations. Using data from eight study sites in Nigeria and elsewhere, we show that our reconstructive computational knowledge discovery system is able to combine information contained within partially-available site-specific monitoring data with knowledge of parasite transmission dynamics embedded in process-based models to generate the missing data required for inducing reliable locally applicable LF models. We also show that the models so discovered are able to generate the intervention forecasts required for supporting management-relevant decisions in parasite elimination.

ecology↗

bioRxiv2019

The fate of carbon in a mature forest under carbon dioxide enrichment

Atmospheric carbon dioxide enrichment (eCO2) can enhance plant carbon uptake and growth1,2,3,4,5, thereby providing an important negative feedback to climate change by slowing the rate of increase of the atmospheric CO2 concentration6. While evidence gathered from young aggrading forests has generally indicated a strong CO2 fertilization effect on biomass growth3,4,5, it is unclear whether mature forests respond to eCO2 in a similar way. In mature trees and forest stands7,8,9,10, photosynthetic uptake has been found to increase under eCO2 without any apparent accompanying growth response, leaving an open question about the fate of additional carbon fixed under eCO24, 5, 7,8,9,10,11. Here, using data from the first ecosystem-scale Free-Air CO2 Enrichment (FACE) experiment in a mature forest, we constructed a comprehensive ecosystem carbon budget to track the fate of carbon as the forest responds to four years of eCO2 exposure. We show that, although the eCO2 treatment of ambient +150 ppm (+38%) induced a 12% (+247 gCm-2yr-1) increase in carbon uptake through gross primary production, this additional carbon uptake did not lead to increased carbon sequestration at the ecosystem level. Instead, the majority of the extra carbon was emitted back into the atmosphere via several respiratory fluxes, with increased soil respiration alone contributing [~]50% of the total uptake surplus. Our results call into question the predominant thinking that the capacity of forests to act as carbon sinks will be generally enhanced under eCO2, and challenge the efficacy of climate mitigation strategies that rely on CO2 fertilization as a driver of increased carbon sinks in standing forests and afforestation projects.

ecology↗

bioRxiv2019

Ecological niche differentiation in soil cyanobacterial communities across the globe

Cyanobacteria are key organisms in the evolution of life on Earth, but their distribution and environmental preferences in terrestrial ecosystems remain poorly understood. This lack of knowledge is particularly evident for two recently discovered non-photosynthetic cyanobacterial classes, Melainabacteria and Sericytochromatia, limiting our capacity to predict how these organisms and the important ecosystem functions they perform will respond to ongoing global change. Here, we conducted a global field survey covering a wide range of vegetation types and climatic conditions to identify the environmental factors associated with the distribution of soil cyanobacterial communities. Network analyses revealed three major clusters of cyanobacterial phylotypes, each one dominated by members of one of the extant classes of Cyanobacteria (Oxyphotobacteria, Melainabacteria and Sericytochromatia), suggesting that species within these taxonomic groups share similar environmental preferences. Melainabacteria appear mostly in acidic and humid ecosystems, especially forests, Oxyphotobacteria are prevalent in arid and semiarid areas, and Sericytochromatia are common in hyperarid oligotrophic environments. We used this information to construct a global atlas of soil cyanobacteria. Our results provide novel insights into the ecology and biogeography of soil cyanobacteria and highlight how their global distribution could change in response to increased aridity, a landmark feature of climate change in terrestrial ecosystems worldwide. Significance statementCyanobacteria have shaped the history of life on Earth and can be important photosynthesizers and nitrogen fixers in terrestrial ecosystems worldwide. The recent discovery of two non-photosynthetic classes has advanced our understanding of their evolution, but their distribution and environmental preferences remain poorly described. Using a global survey conducted across 237 locations on six continents, we identified three main groups of soil cyanobacteria with contrasting environmental preferences: acidic and humid ecosystems, arid and semiarid areas, and hyperarid oligotrophic ecosystems. We then constructed the first global atlas of soil cyanobacteria, an important advance in our understanding of the ecology and biogeography of these functionally important organisms.

ecology↗

bioRxiv2018

IL-11 neutralising therapies target hepatic stellate cell-induced liver inflammation and fibrosis in NASH

The transformation of hepatic stellate cells (HSCs) into myofibroblasts is the defining pathobiology in non-alcoholic steatohepatitis (NASH). Here we show that key NASH factors induce IL-11, which drives an autocrine and ERK-dependent activation loop to initiate and maintain HSC-to-myofibroblast transformation, causing liver fibrosis. IL-11 is upregulated in NASH and Il11ra1-deleted mice are strongly protected from liver fibrosis, inflammation and steatosis in murine NASH. Therapeutic inhibition of IL11RA or IL-11 with novel neutralizing antibodies robustly inhibits NASH pathology in preclinical models and reverses established liver fibrosis by promoting HSC senescence and favourable matrix remodelling. When given early in NASH, IL-11 inhibition prevents liver inflammation and steatosis, reverses severe hepatocyte damage and reduces hepatic immune cells and TGF{beta}1 levels. Our findings show an unappreciated and central role for IL-11 in HSCs and prioritise IL-11 signalling as a new therapeutic target in NASH while revealing an unexpected pro-inflammatory function for IL-11 in stromal immunity.

molecular biology↗