Spred2 Regulates High Fat Diet-Induced Adipose Tissue Inflammation, and Metabolic Abnormalities in Mice

Chronic low-grade inflammation in visceral adipose tissues triggers the development of obesity-related insulin resistance, leading to the metabolic syndrome, a serious health condition with higher risk of cardiovascular disease, diabetes, and stroke. In the present study, we investigated whether Sprouty-related EVH1-domain-containing protein 2 (Spred2), a negative regulator of the Ras/Raf/ERK/MAPK pathway, plays a role in the development of high fat diet (HFD)-induced obesity, adipose tissue inflammation, metabolic abnormalities, and insulin resistance. Spred2 knockout (KO) mice, fed with HFD, exhibited an augmented body weight gain, which was associated with enhanced adipocyte hypertrophy in mesenteric white adipose tissue (mWAT) and deteriorated dyslipidemia, compared with wild-type (WT) controls. The number of infiltrating macrophages with a M1 phenotype, and the crown-like structures, composed of macrophages surrounding dead or dying adipocytes, were more abundant in Spred2 KO-mWAT compared to in WT-mWAT. Exacerbated adipose tissue inflammation in Spred2 KO mice led to aggravated insulin resistance and fatty liver disease. To analyze the mechanism(s) that caused adipose tissue inflammation, cytokine response in mWAT was investigated. Stromal vascular fraction that contained macrophages from Spred2 KO-mWAT showed elevated levels of tumor necrosis factor α (TNFα) and monocyte chemoattractant protein-1 (MCP-1/CCL2) compared with those from WT-mWAT. Upon stimulation with palmitate acid (PA), bone marrow-derived macrophages (BMDMs) derived from Spred2 KO mice secreted higher levels of TNFα and MCP-1 than those from WT mice with enhanced ERK activation. U0126, a MEK inhibitor, reduced the PA-induced cytokine response. Taken together, these results suggested that Spred2, in macrophages, negatively regulates high fat diet-induced obesity, adipose tissue inflammation, metabolic abnormalities, and insulin resistance by inhibiting the ERK/MAPK pathway. Thus, Spred2 represents a potential therapeutic tool for the prevention of insulin resistance and resultant metabolic syndrome

Effects of Iron Amendments on the Speciation of Arsenic in the Rice Rhizosphere after Drainage

Applications of iron- (Fe-) bearing materials represent an effective countermeasure for decreasing the dissolution of arsenic (As) in soil under anaerobic conditions. In this study, we investigated the effects of Fe amendments (ferrihydrite-based and zero-valent iron- (ZVI-) based materials) on the speciation of As in rice cultivated soils and root-attached materials including Fe plaque when the soil shifts from anaerobic to aerobic conditions. Rice (Oryza sativa L.) was cultivated in pots filled with soil under continuous flooding conditions, and root distribution in the soil was restricted inside a cylinder made by nylon mesh. Soil and root samples were collected after drainage at different growth stages of the rice plants, which are represented by intermittent drainage and drainage at harvest. The speciation of As was determined by As K-edge X-ray absorption near edge structure (XANES) spectroscopy. The proportion of arsenite did not differ between the bulk soil and root-attached materials including Fe plaque, whereas a larger proportion of dimethylarsinic acid was found in the root-attached materials regardless of the application of Fe amendments. Observation of soil thin-sections showed that the application of Fe amendments caused an increase in Fe (hydr)oxide deposition around the roots as well as on the soil particles. In addition to Fe (hydr)oxide, sulfide was found to be associated with As under anaerobic conditions, notably for the ZVI-amended soil at the time of intermittent drainage. The concentration of As in the soil solution and As uptake by rice grains decreased, while As speciation near the roots was not influenced by the application of Fe amendments. In conclusion, Fe amendments mitigated As dissolution in the soil solution by providing a sorption site for As in bulk soil without altering As speciation near the roots

Arsenic Distribution and Speciation near Rice Roots Influenced by Iron Plaques and Redox Conditions of the Soil Matrix

Elevated arsenic (As) concentrations in rice and the soil solution result from changes in soil redox conditions, influenced by the water management practices during rice cultivation. Microscale changes in redox conditions from rhizosphere to soil matrix affect the As speciation and Fe plaque deposition. In order to focus on the rhizosphere environment, we observed microscale distribution and speciation of As around the rhizosphere of paddy rice with X-ray fluorescence mapping and X-ray absorption spectroscopy. When the soil matrix was anaerobic during rice growth, Fe-plaque did not cover the entire root, and As­(III) was the dominant arsenic species in the soil matrix and rhizosphere. Draining before harvest led the conditions to shift to aerobic. Oxidation of As­(III) to As­(V) occurred faster in the Fe-plaque than the soil matrix. Arsenic was scavenged by iron mottles originating from Fe-plaque around the roots. The ratio of As­(V) to As­(III) decreased toward the outer-rim of the subsurface Fe mottles where the soil matrix was not completely aerated. These results provide direct evidence that speciation of As near rice roots depends on spatial and temporal redox variations in the soil matrix

Microscale Heterogeneous Distribution and Speciation of Phosphorus in Soils Amended with Mineral Fertilizer and Cattle Manure Compost

Global concerns for the sustainability of agriculture have emphasized the need to reduce the use of mineral fertilizer. Although phosphorus (P) is accumulated in farmland soils due to the long-term application of fertilizer, most soil P is not readily available to plants. The chemical speciation of P in soils, which comprise heterogeneous microenvironments, cannot be evaluated with a high degree of specificity using only macroscopic analyses. In this study, we investigated the distribution and speciation of P accumulated in soils by using both macro- and microscopic techniques including chemical extraction, solution and solid-state 31P NMR, bulk- and micro- P K-edge X-ray absorption near edge structure (XANES), and electron probe microanalysis (EPMA). Soil samples were collected from a field in which cabbage was cultivated under three amendment treatments: i) mineral fertilizer (NPK), ii) mineral fertilizer and compost (NPK + compost), and iii) mineral fertilizer plus compost but without nitrogen fertilizer (PK + compost). Macro-scale analyses suggested that accumulated P was predominantly inorganic P and associated with Al-bearing minerals. The repeated application of compost to the soils increased the proportion of P associated with Ca which accounted for 17% in the NPK + compost plot and 40% in the PK + compost plot. At the microscale, hot spots of P were heterogeneously distributed, and P was associated with Fe and Ca in hot spots of the NPK + compost (pH 6) and PK + compost (pH 7) treated samples, respectively. Our results indicate that application of compost contributed to creating diverse microenvironments hosting P in these soils