Burns, K. | Search bioRxiv

bioRxiv2018

A novel method for comparison of arterial remodeling in hypertension: quantification of arterial trees and recognition of remodeling patterns on histological sections

Remodeling of spatially heterogeneous arterial trees is routinely quantified on tissue sections by averaging linear dimensions, with lack of comparison between different organs and models. The impact of experimental models or hypertension treatment modalities on organ-specific vascular remodeling remains undefined. A wide variety of arterial remodeling types has been demonstrated for hypertensive models, which include differences across organs. The purpose of this study was to reassess methods for measurement of arterial remodeling and to establish a morphometric algorithm for standard and comparable quantification of vascular remodeling in hypertension in different vascular beds. We performed a novel and comprehensive morphometric analysis of terminal arteries in the brain, heart, lung, liver, kidney, spleen, stomach, intestine, skin, skeletal muscle, and adrenal glands of control and Goldblatt hypertensive rats on routinely processed tissue sections. Mean dimensions were highly variable but grouping them into sequential 5 m intervals permitted creation of reliable linear regression equations and complex profiles. Averaged arterial dimensions demonstrated seven remodeling patterns that were distinct from conventional inward-outward and hypertrophic-eutrophic definitions. Numerical modeling predicted at least twenty variants of arterial spatial conformations. Recognition of remodeling variants was not possible using averaged dimensions, their ratios, or the remodeling and growth index. To distinguish remodeling patterns, a three-dimensional modeling was established and tested. The proposed algorithm permits quantitative analysis of arterial remodeling in different organs and may be applicable for comparative studies between animal hypertensive models and in human hypertension. Arterial wall tapering is the most important factor to consider in arterial morphometry, while perfusion fixation with vessel relaxation is not necessary. Terminal arteries in organs undergo the same remodeling pattern in Goldblatt rats, except for organs with hemodynamics affected by the arterial clip. The existing remodeling nomenclature should be replaced by a numerical classification applicable to any type of arterial remodeling.\n\nAuthor summaryArterial hypertension effects modern nations and is characterised by systemic hypertensive angiopathy that affects all organs. Arterial remodeling is a main factor to be analyzed in animal models and human. Despite abundant data, there is a significant lack of comparative analysis on arterial remodeling. The data from the present study have established a novel methodological approach to assess and compare arterial remodeling in hypertension. We have developed an effective algorithm for morphometry of intra-organ arteries to standardize remodeling assessment and allow comparisons between different hypertensive models, organs and species. Our study opens the possibility to assess remodeling using conventional widely used histological tissue sections with no need for special perfusion-fixation. The method will elucidate the improvement and development of animal models of hypertension, and enhance the assessment of experimental therapeutic modalities.

pathology↗

bioRxiv2016

Artificial Microbiome-Selection to Engineer Microbiomes That Confer Salt-Tolerance to Plants

We develop a method to artificially select for rhizosphere microbiomes that confer salt-tolerance to the model grass Brachypodium distachyon. We differentially propagate microbiomes within the background of a non-evolving, highly-inbred plant population, and therefore only microbiomes evolve in our experiment, but not the plants. To optimize methods, we conceptualize artificial microbiome-selection as a special case of indirect selection: We do not measure microbiome properties directly, but we use host performance (e.g., biomass; seed set) as an indicator to infer association with rhizosphere microbiomes that confer salt-tolerance to a plant. We previously called this indirect-selection scheme host-mediated indirect selection on microbiomes (Mueller & Sachs 2015). Our methods aim to maximize evolutionary changes due to differential microbiome-propagation, while minimizing some (but not all) ecological processes affecting microbiome composition. Specifically, our methods aim to maximize microbiome perpetuation between selection-cycles and maximize response to artificial microbiome-selection by (a) controlling microbiome assembly when inoculating seeds at the beginning of each selection cycle; (b) using low-carbon soil to enhance host-control mediated by carbon secretions of plants during initial microbiome assembly and subsequent microbiome persistence; (c) fractionating microbiomes before transfer between plants to perpetuate and select only on bacterial and viral (but not fungal) microbiome components; and (d) ramping of salt-stress between selection-cycles to minimize the chance of over-stressing plants. Our selection protocol generates microbiomes that enhance plant fitness after only 1-3 rounds of artificial selection on rhizosphere microbiomes. Relative to fallow-soil control treatments, artificially-selected microbiomes increase plant fitness by 75% under sodium-sulfate stress, and by 38% under aluminum-sulfate stress. Relative to null control treatments, artificially-selected microbiomes increase plant fitness by 13% under sodium-sulfate stress, and by 12% under aluminum-sulfate stress. When testing microbiomes after nine rounds of differential microbiome propagation, the effect of bacterial microbiomes selected to confer tolerance to sodium-sulfate stress appears specific (these microbiomes do not confer tolerance to aluminum-sulfate stress), but the effect of microbiomes selected to confer tolerance to aluminum-sulfate stress appears non-specific (selected microbiomes ameliorate both sodium- and aluminum-sulfate stresses). Complementary metagenomic analyses of the artificially selected microbiomes will help elucidate metabolic properties of microbiomes that confer specific versus non-specific salt-tolerance to plants.

plant biology↗