Low-dose dopamine hastens onset of gut ischemia in a porcine model of hemorrhagic shock.

Gut metabolism may become anaerobic before the whole body during progressive phlebotomy in dogs. Because dopamine has selective mesenteric vasodilator effects, we asked whether dopamine could delay onset of bowel ischemia during hemorrhagic shock. We studied whole body and gut O2 consumption (VO2) and O2 delivery (QO2) using progressive phlebotomy in anesthetized pigs. Nine pigs received a dopamine infusion of 2 micrograms.kg-1.min-1, whereas a control group of seven pigs received equivalent saline infusion. Onset of ischemia in whole body and gut was determined as critical O2 delivery (QO2c), the intersection point of biphasic regression on plots of VO2-QO2 relationships. Blood flow and O2 extraction were measured as mechanisms of gut ischemia for entire in situ small and large gut using a superior mesenteric venous fistula. Dopamine hastened onset of gut ischemia relative to onset of whole body ischemia (gut critical point in terms of whole body QO2 9.9 +/- 2.1 ml O2.kg-1.min-1, whole body QO2c 7.8 +/- 0.7 ml O2.kg-1.min-1, P less than 0.01). In contrast, onset of gut ischemia in control animals occurred at same time as onset of whole body ischemia (gut critical point in terms of whole body QO2 7.4 +/- 2.3 ml O2.kg-1.min-1, whole body QO2c 7.1 +/- 2.7 ml O2.kg-1.min-1, P = not significant). Hastening of onset of gut ischemia in dopamine-treated animals was associated with decreased ability of gut to extract O2. Low-dose dopamine was not protective against gut ischemia during shock but rather caused earlier onset of gut ischemia during hemorrhagic shock.     

Effect of crystalloid administration on oxygen extraction in endotoxemic pigs

We asked whethercrystalloid administration improves tissue oxygen extraction inendotoxicosis. Four groups of anesthetized pigs(n = 8/group) received either normalsaline infusion or no saline and either endotoxin or no endotoxin. Wemeasured whole body (WB) and gut oxygen delivery and consumption duringhemorrhage to determine the critical oxygen extraction ratio(ER_O2 crit). Just after onset of ischemia (critical oxygen delivery rate), gut was removed for determination of area fraction of interstitial edema and capillary hematocrit. Radiolabeled microspheres were used todetermine erythrocyte transit time for the gut. Endotoxin decreased WBER_O2 crit(0.82 ± 0.06 to 0.55 ± 0.08, P < 0.05) and gutER_O2 crit(0.77 ± 0.07 to 0.52 ± 0.06, P < 0.05). Unexpectedly, saline administration also decreased WBER_O2 crit (0.82 ± 0.06 to 0.62 ± 0.08, P < 0.05) and gutER_O2 crit (0.77 ± 0.07 to 0.67 ± 0.06, P < 0.05) in nonendotoxin pigs. Saline administration increased thearea fraction of interstitial space (P < 0.05) and resulted in arterial hemodilution(P < 0.05) but not capillaryhemodilution (P > 0.05). Salineincreased the relative dispersion of erythrocyte transit times from0.33 ± 0.08 to 0.72 ± 0.53 (P < 0.05). Thus saline administration impairs tissue oxygen extractionpossibly by increasing interstitial edema or increasing heterogeneityof microvascular erythrocyte transit times.

     

The genetics of human obesity

Obesity is an important cause of morbidity and mortality in developed countries, and is also becoming increasingly prevalent in the developing world. Although environmental factors are important, there is considerable evidence that genes also have a significant role in its pathogenesis. The identification of genes that are involved in monogenic, syndromic and polygenic obesity has greatly increased our knowledge of the mechanisms that underlie this condition. In the future, dissection of the complex genetic architecture of obesity will provide new avenues for treatment and prevention, and will increase our understanding of the regulation of energy balance in humans.     

A High-Resolution Tissue-Specific Proteome and Phosphoproteome Atlas of Maize Primary Roots Reveals Functional Gradients along the Root Axes

A high-resolution proteome and phosphoproteome atlas of four maize (Zea mays) primary root tissues, the cortex, stele, meristematic zone, and elongation zone, was generated. High-performance liquid chromatography coupled with tandem mass spectrometry identified 11,552 distinct nonmodified and 2,852 phosphorylated proteins across the four root tissues. Two gradients reflecting the abundance of functional protein classes along the longitudinal root axis were observed. While the classes RNA, DNA, and protein peaked in the meristematic zone, cell wall, lipid metabolism, stress, transport, and secondary metabolism culminated in the differentiation zone. Functional specialization of tissues is underscored by six of 10 cortex-specific proteins involved in flavonoid biosynthesis. Comparison of this data set with high-resolution seed and leaf proteome studies revealed 13% (1,504/11,552) root-specific proteins. While only 23% of the 1,504 root-specific proteins accumulated in all four root tissues, 61% of all 11,552 identified proteins accumulated in all four root tissues. This suggests a much higher degree of tissue-specific functionalization of root-specific proteins. In summary, these data illustrate the remarkable plasticity of the proteomic landscape of maize primary roots and thus provide a starting point for gaining a better understanding of their tissue-specific functions.The maize (Zea mays) root system consists of embryonic primary and seminal roots and postembryonic lateral and shoot-borne roots (Hochholdinger, 2009). The primary root is the first organ that emerges after germination, providing water and nutrients for the growing seedling. The longitudinal structure of maize roots is characterized by a root cap at the terminal end, a subterminal meristematic zone, followed by zones in which newly formed cells elongate and differentiate (Ishikawa and Evans, 1995). The differentiation zone, in which functionally distinct cell types are formed, can be tracked by the presence of epidermal root hairs. Hence, roots represent a gradient of cell differentiation along the longitudinal axis: young and undifferentiated cells are located at the distal end near the root tip, whereas differentiated cells are located toward the proximal end of the root (Ishikawa and Evans, 1995).Radially, maize roots can be divided into the stele and the surrounding cortical parenchyma. The stele comprises vascular and ground tissue, which is enclosed by the single-layered pericycle as the outermost boundary. The multilayered cortical parenchyma comprises, from the center to the periphery, a single ring of endodermis cells, a multilayered cortical parenchyma, and single files of exodermis and epidermis cells connecting the root to the rhizosphere (Hochholdinger, 2009). The epidermis of the differentiation zone is densely populated by tubular root hairs, which are instrumental for the uptake of nutrients that are either transported into the shoot or metabolized in the cortical parenchyma (Marschner, 2011).In recent years, soluble proteomes of whole maize roots were analyzed with respect to development (Hochholdinger et al., 2005), genotypic variation (Hochholdinger et al., 2004; Wen et al., 2005; Liu et al., 2006; Sauer et al., 2006; Hoecker et al., 2008), and environmental interactions (Chang et al., 2000; Li et al., 2007).A major limitation of analyzing whole roots is their composite nature, being made up of distinct tissues. Each tissue provides unique protein accumulation patterns that have the potential to be masked when whole roots are analyzed. This constraint can be overcome by tissue-specific analyses. Thus far, only a few surveys have analyzed distinct tissues such as the primary root tip (Chang et al., 2000), the elongation zone (Zhu et al., 2006, 2007), and cortical parenchyma and stele (Saleem et al., 2010). The mechanical separation of maize root cortical parenchyma (hereafter referred to as cortex) and stele made the most abundant soluble proteins of these tissues accessible (Saleem et al., 2010). Combining two-dimensional gel electrophoresis and electrospray tandem mass spectrometry (MS/MS) identified 59 proteins preferentially expressed in the cortex and 11 proteins predominantly accumulated in the stele (Saleem et al., 2010). Among these proteins, a β-glucosidase functioning in the release of free bioactive cytokinin (Brzobohatý et al., 1993) was preferentially accumulated in the cortical parenchyma (Saleem et al., 2010). That study gave first insights into tissue-specific protein accumulation in the differentiation zone of maize roots. All these initial studies were based on the combination of two-dimensional SDS-PAGE with subsequent mass spectrometric analyses of selected proteins and thus were of limited resolution and depth.More recently, gel-free shotgun proteomics further enhanced the depth of proteomic profiles by quantitative liquid chromatography-MS/MS analyses (Zhu et al., 2010). This technique allowed for the identification of more than 12,000 proteins in a maize leaf developmental time-course experiment (Facette et al., 2013) and a similar number of proteins isolated from developing maize seeds (Walley et al., 2013). These studies provided novel insights into protein accumulation patterns in these maize organs during development, which are instrumental for the better understanding of these biological systems.In this study, we used gel- and label-free high-performance liquid chromatography (HPLC)-MS/MS to quantify the abundance of 11,552 nonmodified proteins and 2,852 phosphoproteins in four distinct tissues of the maize primary root. Proteins unique to certain root tissues or differentially accumulated between root tissues were functionally annotated and analyzed in detail. Moreover, the maize root proteome was compared with maize leaf and seed proteomes of similar size to identify conserved and organ-specific protein accumulation patterns. Furthermore, tissue-specific accumulation patterns of proteins encoded by classical maize genes were surveyed to reveal tissue-specific functions. Finally, proteome and RNA sequencing (RNA-Seq) data of primary root tissues were compared to determine the correlation of these classes of biomolecules.