Evaluation of both upregulated and downregulated genes among the experimental groups were in the direction of inflammation resolution. For example, in the Fat-1 genotype the observed differences in the downregulated genes were associated with cytokine production in macrophages, regulation of tight junctions and ECM disassembly, suggesting a move towards resolution of inflammation in tissue . Cytokine production and tight junctions contribute significantly to the maintenance of epithelial cell integrity and mucosal immunity of the lung in response to environmental insults as well as pathogens . Similarly, changes in ECM are important for recruitment of immune cells into and within the lung . Altogether, changes in these processes promoted by elevated levels of ω-3 fatty acids as in Fat-1 transgenic mice might affect how the lung responds to DE exposure. Particularly with TPPU, we identified down regulation of genes involved in IL-33 mediated signaling, as well as IL-5, IL-13, and IL-6 secretion. Overall, these data identified differences in immune clearance between the two genotypes and TPPU appeared to contribute to T-cell differentiation and regulation of PMN activation in part by downregulating the IL-33-mediated signaling pathway. IL-33 has previously been reported as an important regulator of Th- 2 immune response in allergic inflammation . The studies described herein do have numerous limitations. As with all transgenic animal models, the use of the Fat-1 mice to increase total body tissue levels of ω-3 PUFA and achieve an ideal ∼1:1 ratio of ω-6:ω-3 PUFA does not fully recapitulate the human condition. For example, differences in PUFA intakes are seen not only between individuals,nft hydroponic but temporal fluctuations in diet tendencies for each individual also undoubtedly alter daily to monthly PUFA levels, and the impacts of this will vary across different tissues based on PUFA uptake kinetics .
As PUFA substrate utilized during inflammatory events likely comes from both tissue sources as well as circulating blood and associated inflammatory cell infiltration, the impacts of recent dietary intake versus long-term dietary patterns on PUFA substrate availability are difficult to ascertain. Also, there are numerous recognized health benefits of diets high in ω-3 PUFA, due at least partly to their role in the endogenous production of SPM that regulate inflammation resolution and repair activities . SPM are produced temporally during an inflammatory response; their levels increase within hours to days following an inflammatory insult, and their production is critical to inflammation catabasis, including promoting neutrophil clearance, reducing inflammatory cytokine production, activating M2-like pro-resolution macrophages, promoting regulatory T cell recruitment, and activating tissue repair . Deficiencies in SPM generation pathways have been identified in asthma, and SPM are decreased in lavage, sputum, and/or exhaled breath condensates of COPD and asthma patients compared to individuals without lung disease . Therefore, an in-depth analysis of both ω -3 and ω -6 PUFA derived SPMs is necessary, and lipid metabolomics analyses of our data are currently underway in our laboratory. Another limitation is that we have used a model of organic dust exposure that utilizes a sterile-filtered aqueous extract of environmental dusts that is intranasally instilled to mice in a saline solution. This model will not fully recapitulate the inhalantinjury that is experienced by an individual working in a swine confinement facility, as it does not consider certain components, including live pathogens or gaseous components that have recognized respiratory impacts in these workers . It has been reported that airway inflammation in swine confinement workers differ from naïve subjects even after repetitive exposures, one displaying neutrophilic airway inflammation and the other neutrophilic and eosinophilic inflammation, respectively .
We have characterized a number of components that are likely to be involved in neutrophilic inflammation. Proteases are one of the components of agricultural dust that has been shown to be in part responsible for this type of inflammation . Our results are consistent with neutrophilic inflammation observed in people. In addition, since we delivered agricultural dust extract under light isoflurane anesthesia, the previously reported sex-related differences of isoflurane might confound some of the sex-related effects we observed in our study; however, given all the mice in each group underwent this light anesthesia the significant differences between the groups would still stand. Compelling data indicate the importance of having a balanced ω-6:ω-3 PUFA ratio for optimal health , yet the typical Western diet has a ratio of ∼10–20:1 . This imbalance is considered a driving or compounding factor in chronic inflammatory diseases, with many pro-inflammatory lipids formed from the ω-6 PUFA arachidonic acid, such as leukotrienes, thromboxanes and prostaglandins . It was recently reported that Veterans with COPD and an occupational history that include agricultural work had an ω-6:ω-3 PUFA ratio of ∼50:1 , underscoring the potential vulnerability of this population. Supplementation with ω-3 PUFA has demonstrated health benefits in clinical studies of cystic fibrosis, COPD, and other lung diseases . Thus, increasing ω-3 FA intake, possibly in combination with a reduced intake of ω-6 PUFA, could be an accessible and effective means of preventing and ameliorating airway disease in patients with inflammatory lung diseases such as those caused by agricultural dust exposures. Taken together, our investigations utilizing the Fat-1 mouse model in conjunction with sEH inhibition highlight the potentials of targeting repair/ resolution pathways therapeutically to promote lung protection from environmental dust exposures, and also highlight differences based on sex in the protectiveness offered by these interventions.
In the case of agriculture workers who are chronically inhaling inflammatory dusts, these outcomes hold promise for improving lung health outcomes via both limiting lung inflammation but also promoting repair following injury in this vulnerable population.The current projection for the world population to reach 9 billion by 2050 strikes an alarm when considering global food security. This drives a need, even greater than already present, to ensure sustainable and resilient agricultural systems with maximal crop production. For decades, countless studies have exemplified the benefits of using plant growth promoting rhizobacteria as soil inocula to improve agronomic productivity . Various strains of PGPR are able to fix nitrogen, solubilize phosphorus, sequester iron, suppress stress ethylene production by roots, produce plant growth hormones, antibiotics and anti-fungal compounds, and to enhance competitive exclusion of plant pathogens. The first recorded commercialization of PGPR was the use of rhizobia in 1895 . Since then, over a dozen different genera have been introduced to soils or seeds and many are sold commercially . In fact, Popular Science named Bio-Soil™, a cocktail of over 300 species of PGPR developed at Michigan State University, as one of the top 10 solutions for the future of farming . PGPR can be categorized based on their beneficial traits. For example; a nitrogen fixer would be termed a biofertilizer,nft system an organism emitting plant growth hormones is a phytostimulator, and ones secreting antibiotics and antifungal compounds are bio-control agents. While PGPR offer a multitude of benefits for healthy plant growth and development, this body of work focuses on mineral phosphate solubilizing bacteria and phytostimulators. Root colonization by phytostimulators has been shown to enhance root development, resulting in greater total root surface area and enhanced nutrient and water absorption. In turn, phytostimulators play the greatest role in increasing crop yields in stressed agriculture, as plant-hormone interference can induce plant systemic tolerance to drought, flooding, salinity, and heavy metals . Phosphorus is a macronutrient essential for plant growth and development and current agricultural practices have become reliant on the application of P fertilizers, especially phosphate rock. Consequently, current reservoirs of phosphate rock are expected to become depleted in 50– 100 years . Inorganic P accounts for approximately 35– 70% of total soil P . Plants are able to uptake Pi in its soluble forms . In soils with neutral to slightly acidic pH’s an abundant amount of Pi is available in these soluble compounds, but unfortunately this can result in the loss of P from plant root zones via leaching. Also, Pi forms highly insoluble mineral complexes with Ca in alkaline soils and with Al and Fe in strongly acidic soils, such that it has maximum availability to plants only at near neutral pH . These issues present a challenge as approximately 75% of P added to soil via fertilizers becomes non-plant available Rodr g e and raga, 1999. To release mineral-bound Pi some bacteria have MPS capabilities, typically achieved by the release of organic anions and correspondingly free protons . This lowers the pH of the soil solution and can release P from Ca, Al, and Fe complexes Rodr g e and raga, 1999). Hence, MPS bacteria can function as biological fertilizers, releasing mineral-bound Pi currently present in soils and reducing the need for additional P fertilization. Plant growth promoting microorganisms can affect root development by generating growth hormones or depleting hormones that would otherwise cause stunted root development.
Ethylene, a gaseous phytohormone, is critical for many plant developmental stages. While an initial peak in ethylene concentration in plant tissues is essential for root and stem growth and flower and fruit development, its continued accumulation triggers a cascade of responses including inhibition of root elongation, induction of hypertrophies, acceleration of aging, promotion of senescence and abscission, and inhibition of auxin transport . Ethylene can also inhibit stimulation of cell proliferation and elongation by repressing auxin response factor synthesis . The ethylene-mediated stress response can be activated by many environmental factors such as heavy metal contamination, high salinity, flooding, drought, and phytopathogens. The pathway to ethylene biosynthesis in plants involves the conversion of methionine into S-adenosyl-L-methionine by an enzyme SAM synthetase followed by the hydrolysis of SAM to form 1-aminocyclopropane-1-carboxylic acid by ACC synthase. In the next step, plant produced ACC oxidases bind to ACC with high affinity, with Km values range from about 50– 120 µM, and catalyze the conversion of ACC to ethylene, carbon dioxide and hydrogen cyanide . Conversely, if ACC is exuded from root tissues, root colonizing bacteria can uptake the ACC and use it as a nitrogen source for growth. Microorganisms with ACC deaminase cleave the propane ring of ACC to produce ammonia and α-ketobutyrate, both of which are then metabolized by bacteria . However, ACC deaminase enzymes have low binding affinities for ACC, with Km values ranging from 1.5– 17.5 mM . Thus, it has been suggested that ACC deaminase must be available at 100– 1000 fold greater amounts than ACC oxidase to reduce the accumulation of deleterious ethylene levels in plant tissues . The genetic regulation of the ACC deaminase structural gene, acdS, has been well described for Pseudomonas putida UW4, detailing an intricate regulation promoted by an ACC-bound complex and inhibited by a protein transcribed upstream of acdS, termed the ACC deaminase regulatory protein, AcdR. The intergenic space between these genes has been identified as the P. putida UW4 promoter region for AcdS, where binding of both regulatory complexes occurs . In particular, bacterial strains that generate an auxin compound, indole-3-acetic acid , stimulate total root length, root hair formation, and root branching when colonizing plant rhizospheres . When applied as a seed coat, Enterobacter cloacae UW5 promoted increased root branching and total root length in both mung bean and canola in growth pouch assays . This activity was explicitly linked to IAA production by UW5 . The indole-3-pyruvate pathway is considered to be the major pathway for IAA synthesis in plants and is also utilized by many bacteria . The genetic regulation of a key enzyme, indole-3-pyruvate decarboxylase , involved in this pathway has been well described. Strain UW5 has been shown to have a pathway to IAA production in which the genetic regulation of ipdC is induced by tryptophan . The promoter region of the IpdC gene has a tyrosine transcriptional repressor recognition box . The transcription of ipdC is promoted by the binding of the TyrR box by tryptophan, phenylalanine, and tyrosine, all of which are plant root exudates . The development of commercial bio-fertilizers is difficult as a result of poor or inconsistent survival rates of soil inocula, making quality assessment and verification of any given product very difficult . For example, Acea et al.effectively demonstrated that declines in population densities of soil inocula, such as Pseudomonas, Rhizobium, and Bacillus spps. corresponded to increases in populations of bacterial predators and bacterial competitors . Additionally, direct incorporation of liquid inoculum into soils is complicated by bacterial adhesion to soil particles, which greatly reduces their vertical transport and the ability to colonize roots located in the subsurface soil profile .