Biogeographical survey of soil microbiomes across sub-Saharan Africa: structure, drivers, and predicted climate-driven changes.

BACKGROUND: Top-soil microbiomes make a vital contribution to the Earth's ecology and harbor an extraordinarily high biodiversity. They are also key players in many ecosystem services, particularly in arid regions of the globe such as the African continent. While several recent studies have documented patterns in global soil microbial ecology, these are largely biased towards widely studied regions and rely on models to interpolate the microbial diversity of other regions where there is low data coverage. This is the case for sub-Saharan Africa, where the number of regional microbial studies is very low in comparison to other continents. RESULTS: The aim of this study was to conduct an extensive biogeographical survey of sub-Saharan Africa's top-soil microbiomes, with a specific focus on investigating the environmental drivers of microbial ecology across the region. In this study, we sampled 810 sample sites across 9 sub-Saharan African countries and used taxonomic barcoding to profile the microbial ecology of these regions. Our results showed that the sub-Saharan nations included in the study harbor qualitatively distinguishable soil microbiomes. In addition, using soil chemistry and climatic data extracted from the same sites, we demonstrated that the top-soil microbiome is shaped by a broad range of environmental factors, most notably pH, precipitation, and temperature. Through the use of structural equation modeling, we also developed a model to predict how soil microbial biodiversity in sub-Saharan Africa might be affected by future climate change scenarios. This model predicted that the soil microbial biodiversity of countries such as Kenya will be negatively affected by increased temperatures and decreased precipitation, while the fungal biodiversity of Benin will benefit from the increase in annual precipitation. CONCLUSION: This study represents the most extensive biogeographical survey of sub-Saharan top-soil microbiomes to date. Importantly, this study has allowed us to identify countries in sub-Saharan Africa that might be particularly vulnerable to losses in soil microbial ecology and productivity due to climate change. Considering the reliance of many economies in the region on rain-fed agriculture, this study provides crucial information to support conservation efforts in the countries that will be most heavily impacted by climate change. Video Abstract.

Glucocorticoid binding during the differentiation of 3T3-F442A fibroblasts into adipocytes. A possible regulatory effect of insulin.

Until recently, few studies had been carried out on receptors for glucocorticoids in adipocytes, although the role of these steroids is considerable. In the present studies, we chose the pre-adipocyte line 3T3-F442A, which constitutes an excellent model for investigating the differentiation and function of adipocytes. Using a whole cell assay system, we showed the existence of a homogenous class of sites with the characteristics of glucocorticoid receptors, that is, high-affinity binding which is reversible, specific and saturable. Whatever the state of cellular differentiation, the affinity of the receptor for dexamethasone did not vary, although we observed an increase in the number of sites during differentiation. When cells were differentiated in the presence of insulin, there was a further increase in the binding capacity; moreover, insulin deprivation of such adipocytes caused a decrease in the number of sites. Our results therefore suggest that factors other than the glucocorticoids themselves influence dexamethasone binding. It is suggested that insulin plays a role in the regulation of the number of glucocorticoid receptors.

Development under the control of insulin of lipogenic enzymes, lipoprotein lipase, isoproterenol and glucagon sensitivity in differentiating rat preadipocytes in primary culture.

In preadipose cellular fractions (I, II and III) isolated by density gradient centrifugation from the inguinal tissue of young rats, we followed the activity of fatty acid synthetase, ATP citrate lyase and lipoprotein lipase during differentiation in culture. 1.5 nM insulin when added at confluence markedly induced the activity of ATP citrate lyase and fatty acid synthetase in the cells derived from the lighter fractions (I and II). The magnitude of this response was 25-50-fold the initial value 15 days after plating. In the cells of the heaviest fraction (III) both enzymes exhibited low activity which was slightly stimulated by the presence of insulin, VLDL and heparin. In contrast, the activity of lipoprotein lipase appeared before confluence in cells from all three fractions and peaked at day 6 after plating. This early emergence was independent of the addition of insulin to the medium. However, insulin slightly enhanced the peak activity in post-confluent cells. The development of cAMP production in response to isoproterenol (100 microM) and to glucagon (0.3 microM) was determined in the cells of fraction II in the same culture conditions. The responsiveness to isoproterenol was present very early in these cells and rose rapidly during the exponential growth phase, reaching a peak value at day 8 after plating. In contrast, the development of glucagon sensitivity occurred only during late differentiation. The stimulatory effect of glucagon was enhanced when VLDL and heparin were added with insulin to the medium.

Adipose angiotensinogen is involved in adipose tissue growth and blood pressure regulation.

White adipose tissue and liver are important angiotensinogen (AGT) production sites. Until now, plasma AGT was considered to be a reflection of hepatic production. Because plasma AGT concentration has been reported to correlate with blood pressure, and to be associated with body mass index, we investigated whether adipose AGT is released locally and into the blood stream. For this purpose, we have generated transgenic mice either in which adipose AGT is overexpressed or in which AGT expression is restricted to adipose tissue. This was achieved by the use of the aP2 adipocyte-specific promoter driving the expression of rat agt cDNA in both wild-type and hypotensive AGT-deficient mice. Our results show that in both genotypes, targeted expression of AGT in adipose tissue increases fat mass. Mice whose AGT expression is restricted to adipose tissue have AGT circulating in the blood stream, are normotensive, and exhibit restored renal function compared with AGT-deficient mice. Moreover, mice that overexpress adipose AGT have increased levels of circulating AGT, compared with wild-type mice, and are hypertensive. These animal models demonstrate that AGT produced by adipose tissue plays a role in both local adipose tissue development and in the endocrine system, which supports a role of adipose AGT in hypertensive obese patients.

Angiotensinogen-deficient mice exhibit impairment of diet-induced weight gain with alteration in adipose tissue development and increased locomotor activity.

White adipose tissue is known to contain the components of the renin-angiotensin system, which gives rise to angiotensin II from angiotensinogen (AGT). Recent evidence obtained in vitro and ex vivo is in favor of angiotensin II acting as a trophic factor of adipose tissue development. To determine whether AGT plays a role in vivo in this process, comparative studies were performed in AGT-deficient (agt(-/-)) mice and control wild-type mice. The results showed that agt(-/-) mice gain less weight than wild-type mice in response to a chow or high fat diet. Adipose tissue mass from weaning to adulthood appeared altered rather specifically, as both the size and the weight of other organs were almost unchanged. Food intake was similar for both genotypes, suggesting a decreased metabolic efficiency in agt(-/-) mice. Consistent with this hypothesis, cellularity measurement indicated hypotrophy of adipocytes in agt(-/-) mice with a parallel decrease in the fatty acid synthase activity. Moreover, AGT-deficient mice exhibited a significantly increased locomotor activity, whereas metabolic rate and mRNA levels of uncoupling proteins remained similar in both genotypes. Thus, AGT appears to be involved in the regulation of fat mass through a combination of decreased lipogenesis and increased locomotor activity that may be centrally mediated.

Sequence of rat lipoprotein lipase-encoding cDNA.

A rat lipoprotein lipase (LPL)-encoding cDNA (LPL) has been entirely sequenced and compared to the sequences of all the LPL cDNAs reported in other species. As expected, high homology was found between the coding exons. The putative catalytic triad, Ser132, Asp156, His241, according to human numbering, is conserved in rat. As is the case in mouse, an Asn444 present in human LPL is also missing. The major divergences between human, mouse and rat LPLs were observed in the untranslated exon 10, where (i) the rat cDNA exhibits a 157-bp insertion and an 81-bp deletion relative to human; (ii) neither the B1 repeat nor the homopurine stretch reported in mouse can be recognized, and (iii) the rat cDNA displays several A+T-rich stretches.

Trypanosoma congolense: tissue distribution of long-term T- and B-cell responses in cattle.

Memory T- and B-cell responses to trypanosome antigens were measured in peripheral blood mononuclear cells, spleen and lymph node cells obtained from four trypanotolerant N'Dama cattle which had been exposed to six experimental infections with Trypanosoma congolense. These cattle were treated with trypanocidal drugs following each infection and had remained aparasitemic for 3 years prior to this study. The antigens used were whole trypanosome lysate, variable surface glycoprotein, a 33-kDa cysteine protease (congopain) and a 70-kDa heat-shock protein. As parameters of T-cell-mediated immunity, we measured T-cell proliferation and IFN-gamma production. Lymph node cells, spleen cells and peripheral blood mononuclear cells all proliferated to a mitogenic stimulus (concanavalin A) but only lymph node cells responded to trypanosome antigens. Similarly, IFN-gamma was produced by both lymph node and spleen cells stimulated with concanavalin A but only by lymph node cells stimulated with variable surface glycoprotein and whole trypanosome lysate. T. congolense-specific antibodies were detected in sera and in supernatants of cultured lymph node and spleen cells after in vitro stimulation with lipopolysaccharide and recombinant bovine interleukin-2. In conclusion, we have demonstrated that memory T- and B-cell responses are detectable in various lymphoid organs in cattle 3 years following infection and treatment with T. congolense.

Immunisation of cattle with cysteine proteinases of Trypanosoma congolense: targetting the disease rather than the parasite.

In order to test the hypothesis that trypanosome cysteine proteinases (CPs) contribute to pathology of trypanosomosis, cattle were immunised with CP1 and/or CP2, the major CPs of Trypanosoma congolense, and subsequently challenged with T. congolense. Immunisation had no effect on the establishment of infection and the development of acute anaemia. However, immunised cattle, unlike control cattle, maintained or gained weight during infection. Their haematocrit and leukocyte counts showed a tendency to recovery after 2-3 months of infection. Cattle immunised with CP2 mounted early and prominent IgG responses to CPs and to the variable surface glycoprotein following challenge. Thus trypanosome CPs may play a role in anaemia and immunosuppression; conversely, anti-CP antibody may modulate the trypanosome-induced pathology.

Functional expression of the catalytic domains of two cysteine proteinases from Trypanosoma congolense.

The catalytic domains of two closely related cysteine proteinases (CP1 and CP2) from Trypanosoma congolense, referred to as C1 and C2, were expressed as proforms in Escherichia coli (C1) and in the baculovirus system (C1 and C2). While the bacterial expression system did not allow recovery of active C1, the baculovirus system led to secretion of inactive zymogens which could be processed at acidic pH into mature enzymes. Active C1 and C2 were purified from serum-free culture supernatants by anion-exchange chromatography and characterised. Their kinetic parameters and pH activity profiles confirmed the relatedness between C2 and native CP2 (congopain). These properties also underline major functional differences between C1 and C2, that appear to relate to discrete but essential sequence differences. It is likely that these two enzymes perform distinct roles in vivo, in the parasite and/or in the host-parasite relationships.

Onset and development of hypertriglyceridemia in the Zucker rat (fa/fa).

Triglyceridemia was studied in genetically obese Zucker rats (fa/fa) and their lean littermates aged 1-8 wk. Hypertriglyceridemia was manifest in the obese from 2 wk onwards. Hepatic triacylglycerol secretion rate (TGSR) measured after administration of Triton WR-1339, was similar in obese and lean pups aged 2 wk. At 4 wk TGSR was twice as high in the obese as in the lean. Lipoprotein lipase (LPL) activity was abnormal in the tissues of obese animals, being either increased in white adipose tissue from 1 wk onwards or decreased in brown adipose tissue and cardiac and skeletal muscle from 2 wk onwards. The simultaneous appearance in the 2-wk-old obese of a decrease in LPL activity of the latter tissues, and hypertriglyceridemia strongly suggests a cause-effect relationship particularly since TGRS is normal. After weaning, LPL capacity of white adipose tissue in the obese, although considerably increased, was apparently not high enough to compensate for both an increased TGSR and a decreased LPL activity in other tissues.

Alterations of lipid metabolism and gene expression in rat adipocytes during chronic olanzapine treatment.

Although antipsychotics are established drugs in schizophrenia treatment, they are admittedly known to induce side effects favoring the onset of obesity and worsening its complications. Despite potential involvement of histamine receptor antagonism, or of other neurotransmitter systems, the mechanism by which antipsychotic drugs increase body weight is not elucidated. The aim of the present study was to investigate whether chronic antipsychotic treatments can directly alter the regulation of two main functions of white adipose tissue: lipolysis and glucose utilization. The influence of a classical antipsychotic (haloperidol) was compared to that of two atypical antipsychotics, one known to favor weight gain (olanzapine), the other not (ziprasidone). Cell size, lipolytic capacity and glucose transport activity were determined in white adipocytes of rats subjected to 5-week oral treatment with these antipsychotics. Gene expression of adipocyte proteins involved in glucose transport or fat storage and mobilization, such as glucose transporters (GLUT1 and GLUT4), leptin, matrix metallo-proteinase-9 (MMP9), hormone-sensitive lipase (HSL) and fatty acid synthase (FAS) was also evaluated. Adipocytes from chronic olanzapine-treated rats exhibited decreased lipolytic activity, lowered HSL expression and increased FAS expression. These changes were concomitant to enlarged fat deposition and adipocyte size. Alterations were observed in adipocytes from olanzapine-treated rats whereas the other antipsychotics did not induce any notable disorder. Our results therefore show evidence of an effect of chronic antipsychotic treatment on rat adipocyte metabolism. Thus, impairment of fat cell lipolysis should be considered as a side effect of certain antipsychotics, leading, along with the already documented hyperphagia, to the excessive weight gain observed in patients under prolonged treatment..

Long-term treatment with interleukin-1beta induces insulin resistance in murine and human adipocytes.

AIMS/HYPOTHESIS: Adipose tissue inflammation has recently been implicated in the pathogenesis of insulin resistance and is probably linked to high local levels of cytokines. IL1B, a proinflammatory cytokine, may participate in this alteration. MATERIALS AND METHODS: We evaluated the chronic effect (1-10 days) of IL1B (0.1-20 ng/ml) on insulin signalling in differentiating 3T3-F442A and differentiated 3T3-L1 murine adipocytes and in human adipocytes. We also assessed expression of the gene encoding IL1B in adipose tissue of wild-type and insulin-resistant mice (diet-induced and genetically obese ob/ob mice). RESULTS: IL1B inhibited insulin-induced phosphorylation of the insulin receptor beta subunit, insulin receptor substrate 1, Akt/protein kinase B and extracellular regulated kinase 1/2 in murine and human adipocytes. Accordingly, IL1B suppressed insulin-induced glucose transport and lipogenesis. Long-term treatment of adipose cells with IL1B decreased cellular lipid content. This could result from enhanced lipolysis and/or decreased expression of genes involved in lipid metabolism (acetyl-CoA carboxylase, fatty acid synthase). Down-regulation of peroxisome proliferating-activated receptor gamma and CCAAT/enhancer-binding protein alpha in response to IL1B may have contributed to the altered phenotype of IL1B-treated adipocytes. Moreover, IL1B altered adipocyte differentiation status in long-term cultures. IL1B also decreased the production of adiponectin, an adipocyte-specific protein that plays a positive role in insulin sensitivity. Expression of the gene encoding IL1B was increased in epididymal adipose tissue of obese insulin-resistant mice. CONCLUSIONS/INTERPRETATION: IL1B is upregulated in adipose tissue of obese and insulin-resistant mouse models and may play an important role in the development of insulin resistance in murine and human adipose cells.

A 69 kDa immunodominant antigen of Trypanosoma (Nannomonas) congolense is homologous to immunoglobulin heavy chain binding protein (BiP).

An immunodominant antigen in Trypanosoma congolense-infected cattle is a 69 kDa protein which is conserved among species and developmental stages of African trypanosomes. Immunoscreening of a cDNA expression library identified a 2.35 kbp clone which contains a complete open reading frame encoding a protein of 653 amino acids with a predicted molecular mass of 71 kDa. Protein sequence analyses revealed 45-65% identity with hsp70s from a broad range of organisms, the highest homology being with the mammalian BiP (immunoglobulin heavy chain binding protein). The 69 kDa trypanosome protein shares with other BiP-related molecules two characteristics that are associated with their localization in the endoplasmic reticulum and their function as chaperonins, i.e., a hydrophobic N-terminal signal sequence and a conserved C-terminal tetrapeptide (X)DEL. Divergence between the 69 kDa antigen and other BiP-homologues occurs in the C-terminal region. This may be responsible for the high immunogenicity of the trypanosome protein. The gene for the 69 kDa antigen appears to be present as a cluster of several copies which are not organized in tandem repeats. It is expressed in all developmental stages of T. congolense, but the specific mRNA levels are higher in metacyclics than in other stages.

Lipoprotein lipase at onset of obesity induced in rats by a high-fat diet.

Obesity is detectable in adult male Wistar rats three weeks after initiation of a high-fat diet. Although there was an immediate increase in muscle lipoprotein lipase (LPL) activity, and a progressive adaptative response in adipose tissue leading to inhibition of de-novo lipogenesis, loss of insulin sensitivity and decreased functional LPL activity, the ensuing reorientation of lipid metabolism failed to prevent obesity. It is concluded that there is no fixed relationship between enlargement of adipose tissue and LPL activity in this tissue, at onset of obesity.

Phenotypic variability in unweaned 3-week-old Zucker rats.

At 3 weeks of age, Zucker rats could not be classified as normal or obese according to body or liver weight. On the other hand, determination of subcutaneous adipose tissue weight per 100 grams of body weight permitted both phenotypes to be distinguished, provided that the growth variations particular to each litter were taken into account. Rats whose future obesity is predictable using this method, have significantly elevated serum levels of triacylglycerols, total cholesterol and phospholipids. However, further analysis of these values indicated that in fact there were two subgroups of both obese and non-obese rats, i.e., those which had elevated serum lipid levels and those which did not.

Onset of genetic obesity in the absence of hyperphagia during the first week of life in the Zucker rat (fa/fa).

The aim of this study was to discover which of three major abnormalities of the genetically obese Zucker rat (fa/fa), namely hyperphagia, excess adiposity, and hyperlipidemia, is the first to appear prior to manifest obesity, i.e., before weaning. Suckling fa/fa rats, bred from heterozygous parents, were detected by sizing fat cells obtained from an inguinal fat pad biopsy. Cell hypertrophy was observed in fa/fa rats, compared to Fa/-littermates of the same sex, as soon as 5-7 days after birth. Prediction of fa/fa genotype at this age by this method was assessed using a series of 80 pups and proved to be totally successful. The identity of the "predicted" obese pups was confirmed morphologically at 6 weeks of age. Food (milk) intake was estimated from water turnover rates determined on 86 pups aged 2-8 days using tritiated water. The results show that 7-day-old fa/fa rats had heavier inguinal fat pads with larger adipocytes and higher lipoprotein lipase activity than their lean controls. There was no genotype effect on water intake adjusted to body weight during the first week of life. Moreover weight of stomach contents and triglyceridemia were similar in all animals at 7 days. These results show that excess adiposity develops in the fa/fa rat during the first week of life, before hypertriglyceridemia and hyperphagia, and raises the question of whether this adiposity results from a defect in energy expenditure or an abnormality of fat cell storage capacity, or both.

Trypanosoma congolense: a comparison of T-cell-mediated responses in lymph nodes of trypanotolerant and trypanosusceptible cattle during primary infection.

A comparison of T-cell-mediated immune responses in trypanotolerant N'Dama and susceptible Boran cattle during primary infection with tsetse-transmitted Trypanosoma congolense was conducted to assess whether different patterns of T-cell activation occurred during trypanosome infection. Proliferation and IFN-gamma synthesis in response to trypanosome antigens and to the mitogen Con A were measured in LNC before infection and 10 and 35 days postinfection. Phenotypic analysis of LNC was also carried out. No significant differences in the in vitro proliferation of LNC to VSG, to hsp70/BiP, or to Con A were detected between the breeds. In contrast, IFN-gamma production in response to Con A was higher in Boran cattle at 35 days p.i. A reduction in the number of CD2+ and CD4+ T-cells and an increase in the percentage of B-cells, CD8+ T-cells, and gamma delta T-cells during infection in both N'Dama and Boran was revealed by cytofluorimetric analysis of lymph node cells.

[Lipid metabolism in the newborn genetically obese (fa/fa) rat]. / Métabolisme lipidique chez le rat nouveau-né génétiquement obèse (fa/fa).

Compared to its lean litter mate (Fa/--) the Zucker rat (fa/fa) develops obesity without hyperphagia in the first week of lite. It is characterized by adipocyte hypertrophy and higher lipid content in adipose tissue. In vitro utilization as well as in vitro oxidation by diaphragm of palmitic acid was decreased in 1 week old Zucker rat.

Genetic approach of family obesity: study of HLA antigens in 10 families and 86 unrelated obese subjects.

HLA A and B typing was performed in 86 unrelated obese subjects and in 10 families including at least one parent and one obese sibling. The results in the series of unrelated subjects show no significant difference in antigen frequencies as compared to the control series. However in the 10 families studied, a group of 5 families is characterized by a high penetrance of obesity. In this group, inheritance of obesity seems to be transmitted through a dominant mode, and antigen B 18 appeared 4 times out of 5. The possible existence of a genetic form of obesity is considered in the discussion.