Membrane Sites Research Articles

Renal glycosuria as a novel early sign of colistin-induced kidney damage in mice.

The polymixin colistin represents a last resort antibiotic for multidrug resistant infections, but its use is limited by the frequent onset of acute drug-induced kidney injury (DIKI). It is essential to closely monitor kidney function prior to and during colistin treatment in order to pinpoint early signs of injury and minimise long-term renal dysfunction. To facilitate this, a mouse model of colistin-induced nephrotoxicity was used to uncover novel early markers of colistin-induced DIKI. Increased urinary levels of kidney injury molecule 1 (Kim-1) as well as glycosuria were observed in colistin-treated mice, where alterations of established clinical markers of acute kidney injury (serum creatinine and albuminuria) and emerging markers such as cystatin C were inaccurate in flagging renal damage as confirmed by histology. A direct interaction of colistin with renal glucose reabsorption was ruled out by a cis-inhibition assay in mouse brush border membrane vesicles (BBMV). Immunohistochemical examination and protein quantification by western blotting showed a marked reduction in the protein amount of sodium-glucose transporter 2 (Sglt2), the main kidney glucose transporter, in renal tissue from colistin-treated mice in comparison to control animals. Consistently, BBMV isolated from treated mouse kidneys also showed a reduction in ex vivo glucose uptake when compared to BBMV isolated from control kidneys. These findings support pathology observations of colistin-induced proximal tubule damage at the site of the brush border membrane, where Sglt2 is expressed, and open avenues for the study of glycosuria as a sensitive, specific, and accessible marker of DIKI during colistin therapy.

1727. Candida albicans Phosphatidylinositol-(4,5)-Bisphosphate (PIP2) Directs Aberrant Cytokinesis and Septation in Response to Echinocandins, Which Correlates with Fungicidal Activity and Attenuated Virulence

BackgroundWe previously showed that highly dynamic PIP2, septin, and PKC-Mkc1 cell wall integrity pathway responses correlate with echinocandin activity against C. albicans and attenuated virulence during invasive candidiasis. Our objectives were to determine whether PIP2 dysregulation in response to an echinocandin results in aberrant localization of the septation and cytokinesis apparatus, and to quantitate aberrant localization.MethodsLive cell imaging (LCI) was performed for 3 hours (Nikon A1 confocal microscope, NIS Elements software; Tokyo) on C. albicans irs4 mutant and wild-type SC5314 expressing fluorescently labeled PIP2 and Cdc10 (septin), Act1 (actin), or Myo1 (myosin).Results C. albicans irs4, in which PIP2 5’-phosphatase is disrupted, mislocalizes PIP2 and septins, and over-activates the PKC-Mkc1 pathway in a manner similar to echinocandin-exposed C. albicans SC5314. LCI revealed that PIP2 co-localized with Act1 and Myo1 at aberrant sites in C. albicans irs4, similar to PIP2-Cdc10 co-localization. 83% of co-localizing patches were in cells undergoing active cytokinesis. 78% of patches were at sites of cytokinesis, which reflected both normal budding and abnormal, wide-necked budding; 5% of patches localized to aberrant plasma membrane sites during cytokinesis. 17% of co-localizing patches were in cells that were not undergoing active cytokinesis. 6% of patches were at old cytokinesis sites; 11% of patches were at aberrant plasma membrane sites. Similar PIP2-septin-actin-myosin dysregulation was observed in C. albicans SC5314 immediately upon 4x MIC caspofungin exposure (Figure; videos).ConclusionDysregulated C. albicans PIP2 recruits the septation and cytokinesis apparatus, including septins, actin, and myosin, to sites of incomplete cytokinesis at bud necks and to sites of aberrant, ectopic septation in plasma membranes of both dividing and non-dividing cells. Our data support a model in which a dysregulated PIP2 response is triggered immediately upon echinocandin exposure, over-activates the PKC-Mkc-1 pathway, and correlates with the extent of fungicidal activity and attenuated virulence. PIP2-septation-cytokinesis dysregulation is likely to lead to C. albicans death by promoting cell lysis, or selecting cells to undergo apoptosis. Disclosures All authors: No reported disclosures.

Electrodialysis applied for phenylacetic acid separation from organic impurities: Increasing the recovery

Phenylacetic acid produced biotechnologically is present in phosphate buffer medium containing also organic impurities after production stage. Main aim of this work was to test applicability of electrodialysis for phenylacetic acid separation from organic impurities. Relatively high amounts of phenylacetic acid can be adsorbed on active sites of membranes at the end of electrodialysis process. Electrodialysis of model fermentation broth containing phosphate buffer, phenylacetic acid and organic impurities was conducted in two stages. In the first stage, separation of phenylacetic acid from organic impurities occurs and in the second one, phenylacetic acid bound to active sites of the anion-exchange membrane is displaced by an inorganic anion. Both stages of electrodialysis were performed under constant voltage of either 5 V or 10 V. Recoveries reached after the first stage were higher at 10 V with the highest recovery ratio of 60%. The highest reached recovery ratio of phenylacetic acid after the second electrodialysis stage was 95%.

Impact of site and size of pars tensa tympanic membrane perforation on the success rate of myringoplasty

ObjectiveThis article is intended to investigate the impact of size and site of tympanic membrane (TM) perforation on the outcome and success rate of myringoplasty.Patients and methodsThis prospective study was conducted at Assiut University Hospital, between September 2015 and November 2017. Video-otoscopy was done to all cases, the images were registered on the computer and analyzed by using Universal Desktop Ruler V.3.5.3364 program, as the area of TM perforation (P) and the entire area of TM (T) were calculated. Thereafter, the percentage area of the perforation (P/T×100%) for the perforated ear was revealed. Site of perforation was also authenticated. Preoperative and postoperative A–B gap was carried out through audiogram for hearing results.ResultsThe overall success rate of myringoplasty was 78.8%. According to size of TM perforation; the highest success rate of myringoplasty established between small perforations was 93.3% and the lowest found between subtotal perforations was 42.9%; in medium and large perforations, the success rate of myringoplasty was 87.5 and 71.4%, respectively. As regards the site of TM perforation, the success rate of myringoplasty was highest (90%) for posterior perforations and lowest (70%) for anterior perforations; in central and inferior perforations, the success rate of myringoplasty was 79.8 and 75%, respectively. After myringoplasty, the amount of closure of A–B gap was 21.82 dB.ConclusionThe size of TM perforation has a great influence on the success rate of myringoplasty, while the site of TM perforation has no impact on the success rate of myringoplasty, and myringoplasty is an effective operation for sealing off TM perforations, resulting in improvement of quality of life.

1371P - Genomic landscape of primary malignant melanoma of esophagus

BackgroundAnti-PD-1 monoclonal antibody monotherapy achieves poor outcomes in mucosal melanoma, but our previous study has demonstrated that primary malignant melanoma of esophagus (PMME) has a dramatically high response rate (ORR 75%). The genomic landscape of PMME and reasons for this finding have not been extensively investigated. MethodsWhole exome sequencing were performed in seven treatment-naive PMME tumor samples and matched normal tissues, and genomic data of eight mucosal melanomas was obtained from the International Cancer Genome Consortium. Comprehensive profiling was performed to analyze the of genetic differences of PMME with mucosal melanoma. ResultsThe mean depth of coverage was 268X (ranged from 100X to 400X), 1203 SNV/InDels were detected in seven PMME samples, with a mean value of 172 mutations. The median tumor mutation burden (TMB) was 3.58 mutations/Mb (range 0.19-9.58 mutations/Mb), which was significantly than mucosal melanoma (P=0.021). The mutation spectrum of SNVs displayed more frequency of T>A transition while less frequency of C>T transversion compared to mucosal melanoma. There were 36 genes found to be mutated in more than two PMME tumor samples, and the most significantly mutated genes were CFH (42.9%, 3/7) and MUC16 (42.9%, 3/7). Both BRAF and NRAS were only found in one sample, and no NF1, KIT and SF3B1 mutation were detected. In total, 671 CNVs were detected, and the most frequently amplification chromosomal regions were 10q and 1p, while most frequently deletion in 1q and 8q. Genetic aberrations were mainly enriched in RTK/RAS and WNT pathways. ConclusionsThe TMB is higher in PMME compared to mucosal melanoma, with the highest mutation frequency in CFH and MUC16. CFH has a critical role in the regulation of complement activation, and MUC16 has been reported to be associated with higher tumor mutation load and outcomes in gastric cancer. In summary, our study reveals that the genomic landscape of PMME is different from mucosal melanoma originates from other mucosal membrane sites, and indicates that CFH and MUC16 mutation might be associated with better response to anti-PD-1 monoclonal antibody in PMME patients. Legal entity responsible for the studyPeking University Cancer Hospital-Beijing Cancer Hospital. FundingBeijing Talents Foundation (2016000021223ZK18), National Natural Science Foundation of China (81672696, 81402264). DisclosureAll authors have declared no conflicts of interest.

Filaments and phenotypes: cellular roles and orphan effects associated with mutations in cytoplasmic intermediate filament proteins.

Cytoplasmic intermediate filaments (IFs) surround the nucleus and are often anchored at membrane sites to form effectively transcellular networks. Mutations in IF proteins (IFps) have revealed mechanical roles in epidermis, muscle, liver, and neurons. At the same time, there have been phenotypic surprises, illustrated by the ability to generate viable and fertile mice null for a number of IFp-encoding genes, including vimentin. Yet in humans, the vimentin ( VIM) gene displays a high probability of intolerance to loss-of-function mutations, indicating an essential role. A number of subtle and not so subtle IF-associated phenotypes have been identified, often linked to mechanical or metabolic stresses, some of which have been found to be ameliorated by the over-expression of molecular chaperones, suggesting that such phenotypes arise from what might be termed “orphan” effects as opposed to the absence of the IF network per se, an idea originally suggested by Toivola et al. and Pekny and Lane.

Tailor-Made Specific Recognition of Cyromazine Pesticide Integrated in a Potentiometric Strip Cell for Environmental and Food Analysis.

Screen-printed ion-selective electrodes were designed and characterized for the assessment of cyromazine (CYR) pesticide. A novel approach is to design tailor-made specific recognition sites in polymeric membranes using molecularly imprinted polymers for cyromazine (CR) determination (sensor I). Another sensor (sensor II) is the plasticized PVC membrane incorporating cyromazine/tetraphenyl borate ion association complex. The charge-transfer resistance and water layer reached its minimal by incorporating Polyaniline (PANI) solid-contact ISE. The designed electrodes demonstrated Nernstain response over a linear range 1.0 × 10−2–5.2 × 10−6 and 1.0 × 10−2–5.7 × 10−5 M with a detection limit 2.2 × 10−6 and 8.1 × 10−6 M for sensors I and II, respectively. The obtained slopes were 28.1 ± 2.1 (r2 = 0.9999) and 36.4 ± 1.6 (r2 = 0.9991) mV/decade, respectively. The results showed that the proposed electrodes have a fast and stable response, good reproducibility, and applicability for direct measurement of CYR content in commercial pesticide preparations and soil samples sprayed with CYR pesticide. The results obtained from the proposed method are fairly in accordance with those using the standard official method.

Abstract P2027: Preliminary Characterization Of The 125 I-angiotensin 1-7 Binding Site In Rat Liver

Angiotensin 1-7 (Ang 1-7) is a product of the renin-angiotensin system (RAS) that can reduce blood pressure and fibrosis. For more than a decade Mas has been viewed as the receptor for Ang 1-7, however, there are lingering doubts regarding the nature of the interaction between the heptapeptide and Mas. To date, no one has pharmacologically characterized Ang 1-7 binding in tissue membrane preparations. In this study we show that 125 I-Ang 1-7 binds to a site for which Ang 1-7 has low (μmolar) affinity, suggesting that the addition of an iodine molecule to the tyrosine in position 4 of Ang 1-7 drastically changes the characteristics of this peptide making it unsuitable for characterization of Ang 1-7 receptors. 125 I-Ang 1-7 binds with moderately high affinity (10-20 nM) and saturability to a binding site in rat liver membranes that is displaceable by 127 I-Ang 1-7 (iodoAng 1-7) at nanomolar concentrations. This binding is also displaceable by inhibitors of metalloproteases. To test the hypothesis that 125 I-Ang 1-7 binds to a peptidase, a series of peptidase inhibitors were evaluated for their ability to inhibit 125 I-Ang 1-7 binding. The non-selective matrix metalloprotease (MMP) and A Disintegrin And Metalloprotease (ADAM) inhibitors marimastat, batimastat, and GM-6001, which inhibit MMP1,2,3,7,8,13,14 and ADAM 9,17, partially inhibited 125 I-Ang 1-7 binding with nanomolar affinities, similar to their IC 50 values for MMPs, suggesting that 125 I-Ang 1-7 binds to MMPs and/or ADAMs as well as other tissue elements. Further testing with the specific MMP-2 (ARP100), MMP-9 and ADAM-17 inhibitors indicate that 125 I-Ang 1-7 is not binding to these peptidases. Continuing studies are underway to establish conditions under which the 125 I-Ang 1-7 ligand is not metabolized by peptidases, while retaining the ability to bind to peptidases is underway to enable the identification of the specific peptidase(s) or other binding moieties to which 125 I-Ang 1-7 binds to determine their potential therapeutic importance as a druggable targets.

Glomerular permeability is not affected by heparan sulfate glycosaminoglycan deficiency in zebrafish embryos

Proteinuria develops when specific components in the glomerular filtration barrier have impaired function. Although the precise components involved in maintaining this barrier have not been fully identified, heparan sulfate proteoglycans are believed to play an essential role in maintaining glomerular filtration. Although in situ studies have shown that a loss of heparan sulfate glycosaminoglycans increases the permeability of the glomerular filtration barrier, recent studies using experimental models have shown that podocyte-specific deletion of heparan sulfate glycosaminoglycan assembly does not lead to proteinuria. However, tubular reabsorption of leaked proteins might have masked an increase in glomerular permeability in these models. Furthermore, not only podocytes but also glomerular endothelial cells are involved in heparan sulfate synthesis in the glomerular filtration barrier. Therefore, we investigated the effect of a global heparan sulfate glycosaminoglycan deficiency on glomerular permeability. We used a zebrafish embryo model carrying a homozygous germline mutation in the ext2 gene. Glomerular permeability was assessed with a quantitative dextran tracer injection method. In this model, we accounted for tubular reabsorption. Loss of anionic sites in the glomerular basement membrane was measured using polyethyleneimine staining. Although mutant animals had significantly fewer negatively charged areas in the glomerular basement membrane, glomerular permeability was unaffected. Moreover, heparan sulfate glycosaminoglycan-deficient embryos had morphologically intact podocyte foot processes. Glomerular filtration remains fully functional despite a global reduction of heparan sulfate.

Tomographic evaluation of the influence of the placement of a collagen membrane subjacent to the sinus mucosa during maxillary sinus floor augmentation: a randomized clinical trial

AimTo study the influence of a collagen membrane placed subjacent to the sinus mucosa on the dimensional changes of augmented maxillary sinus floor.MethodsTwenty patients were recruited in the study and randomly assigned to two groups. After the elevation of the maxillary sinus mucosa, a collagen membrane with standardized dimensions was placed at the test sites subjacent to the sinus mucosa and the elevated space was filled with a xenograft, both at test and control sites. A collagen membrane was then used to cover the antrostomy at both sites, and sutures were applied to close the wounds. Cone beam computed tomographies (CBCTs) were taken for all patients before surgery (T0), after 1 week from sinus floor augmentation (T1), and after 9 months of healing (T2). Dimensional changes over time of soft and hard tissues were evaluated on the CBCTs.ResultsAfter 1 week of healing, the sinus floor was elevated by 10.0 ± 2.8 mm and 10.6 ± 2.5 mm at the no-membrane and membrane groups, respectively. After 9 months of healing, a similar reduction of the height was observed in both groups, providing a total vertical augmentation of 8.6 ± 2.8 mm at the no-membrane sites and 9.1 ± 3.1 mm at the membrane sites. After 9 months of healing, the hard tissues subjacent to the sinus mucosa appeared to be partially corticalized in three patients in the no-membrane group and in six patients in the membrane group.ConclusionsThe use of collagen membranes subjacent to the sinus mucosa did not influence the dimensional variations of the augmented regions and the clinical outcomes after 9 months of healing also in absence of perforations.

Blocked-D phenomenon in hemolytic disease of fetus and newborn with multiple maternal antirhesus antibodies

Background: The blocking of D antigen sites of RBC membrane of the fetus by the passively transferred IgG anti-D in cases of Hemolytic Disease of fetus and new born (HDFN) is called blocked- D phenomenon. The coating of maternal IgG type of anti-D prevents the agglutination of the Rh-(D) antigen positive red blood cells (RBC) by the IgM D-antigen typing reagents. We are reporting two cases of Rh-(D) HDFN which were falsely typed as Rh (D) antigen negative with routine typing reagents and had multiple allo-antibodies in the maternal serum. Aims: To rule out HDFN and to confirm the Rh-(D) status of baby, to detect the presence of other allo-antibodies in the maternal serum that can complicate future transfusions in mother. Materials: After routine blood grouping, sample of baby was subjected to adsorption-elution studies and maternal serum was used for antibody screening and identification Results: In both the cases, blocked-D phenomenon got detected and there were multiple anti-rhesus antibodies other than anti-D in the maternal serum. Conclusion: Antibody identification in antenatal women is important in the case management of HDFN to protect future pregnancies and to avoid the risk of mismatched transfusions.

Perfringolysin O-Induced Plasma Membrane Pores Trigger Actomyosin Remodeling and Endoplasmic Reticulum Redistribution.

Clostridium perfringens produces an arsenal of toxins that act together to cause severe infections in humans and livestock animals. Perfringolysin O (PFO) is a cholesterol-dependent pore-forming toxin encoded in the chromosome of virtually all C. perfringens strains and acts in synergy with other toxins to determine the outcome of the infection. However, its individual contribution to the disease is poorly understood. Here, we intoxicated human epithelial and endothelial cells with purified PFO to evaluate the host cytoskeletal responses to PFO-induced damage. We found that, at sub-lytic concentrations, PFO induces a profound reorganization of the actomyosin cytoskeleton culminating into the assembly of well-defined cortical actomyosin structures at sites of plasma membrane (PM) remodeling. The assembly of such structures occurs concomitantly with the loss of the PM integrity and requires pore-formation, calcium influx, and myosin II activity. The recovery from the PM damage occurs simultaneously with the disassembly of cortical structures. PFO also targets the endoplasmic reticulum (ER) by inducing its disruption and vacuolation. ER-enriched vacuoles were detected at the cell cortex within the PFO-induced actomyosin structures. These cellular events suggest the targeting of the endothelium integrity at early stages of C. perfringens infection, in which secreted PFO is at sub-lytic concentrations.

Microdosimetric Realistic Model of a Cell with Endoplasmic Reticulum.

When investigating the biophysical effects induced by the interaction between electromagnetic fields and biological cells, it is crucial to estimate the electromagnetic field intensity at the microscopic scale (microdosimetry). This information allows to find a connection between the external applied field and the observed biological event required to establish related biomedical applications. Here, authors present a microdosimetric study based on a 2D realistic model of a cell and its endoplasmic reticulum. The microdosimetric analysis of the cell and endoplasmic reticulum was quantified in terms of electric field and transmembrane potential induced by an externally applied high amplitude 10-ns pulsed electric field. In addition, electroporated local membrane sites and pore densities were also evaluated. This study opens the way to numerically assist experimental applications of nanosecond pulsed electric fields for controlled bio-manipulation of cells and subcellular organelles.

Membrane curvature induces cardiolipin sorting

Cardiolipin is a cone-shaped lipid predominantly localized in curved membrane sites of bacteria and in the mitochondrial cristae. This specific localization has been argued to be geometry-driven, since the CL’s conical shape relaxes curvature frustration. Although previous evidence suggests a coupling between CL concentration and membrane shape in vivo, no precise experimental data are available for curvature-based CL sorting in vitro. Here, we test this hypothesis in experiments that isolate the effects of membrane curvature in lipid-bilayer nanotubes. CL sorting is observed with increasing tube curvature, reaching a maximum at optimal CL concentrations, a fact compatible with self-associative clustering. Observations are compatible with a model of membrane elasticity including van der Waals entropy, from which a negative intrinsic curvature of −1.1 nm−1 is predicted for CL. The results contribute to understanding the physicochemical interplay between membrane curvature and composition, providing key insights into mitochondrial and bacterial membrane organization and dynamics.

Elucidating the Electrode/Electrolyte Interface of Anionic Exchange Membrane Electrolyzers

Anion exchange membrane electrolyzers (AEMEs) have the potential to dramatically decrease the cost of hydrogen production by enabling the use of non-platinum group metal (non-PGM) catalysts. While optimum performance is achieved using hydroxide electrolyte solution, corrosion issues require corrosion resistant system components. Recently, it has been demonstrated that using a carbonate solution as an electrolyte feed for the OER electrode has the potential of significantly lowering the overvoltage. Using carbonate in an AEM interface is however counterintuitive from the point of view of its lowering ionic conductivity, electrode poisoning and mass transport. Initial results from a multiphase, multiphysics computational model of the electrode/electrolyte interface reveal advantages and disadvantages of using a carbonate feed. In terms of the former, the presence of carbonate results in a 1000x increase of the active surface area relative to water. However, the hydroxide flux at the anode causes an accumulation of carbonate ions at the anode resulting in a localized pH shift and Nerstian voltage loss. In addition, carbonate adsorption at the exchange site of the ionomer membrane restricts the use of a carbonate solution to solely the anode. The computational model developed in the course of this research will be used to further characterize the AEME electrode/electrolyte interface. Observations gleaned from the model will be reconciled with performance data obtained from an AEME using non-PGM using various electrolyte feeds across each electrode.

Nonglucuronidated Ezetimibe Disrupts CD13- and CD64-Coassembly in Membrane Microdomains and Decreases Cellular Cholesterol Content in Human Monocytes/Macrophages.

Ezetimibe (EZE) and glucuronidated EZE (EZE-Glu) differentially target Niemann-Pick C1-like 1 (NPC1L1) and CD13 (aminopeptidase-N) to inhibit intestinal cholesterol absorption and cholesterol processing in other cells, although the precise molecular mechanisms are not fully elucidated. Cellular effects of EZE, EZE-Glu, and the low-absorbable EZE-analogue S6130 were investigated on human monocyte-derived macrophages upon loading with atherogenic lipoproteins. EZE and S6130, but not EZE-Glu disturbed the colocalization of CD13 and its coreceptor CD64 (Fcγ receptor I) in membrane microdomains, and decreased the presence of both receptors in detergent-resistant membrane fractions. Biotinylated cholesterol absorption inhibitor C-5 (i.e., derivative of EZE) was rapidly internalized to perinuclear tubular structures of cells, resembling endoplasmic reticulum (ER), but CD13 was detected on extracellular sites of the plasma membrane and endolysosomal vesicles. Administration of EZE, but not of EZE-Glu or S6130, was associated with decreased cellular cholesteryl ester content, indicating the sterol-O acyltransferase 1 (SOAT1)-inhibition by EZE. Furthermore, EZE decreased the expression of molecules involved in cholesterol uptake and synthesis, in parallel with increased apolipoprotein A-I-mediated cholesterol efflux and upregulation of efflux-effectors. However, NPC1L1 the other claimed molecular target of EZE, was not detected in macrophages, thereby excluding this protein as target for EZE in macrophages. Thus, EZE is very likely a CD13-linked microdomain-disruptor and SOAT1-inhibitor in macrophages leading to in vitro anti-atherosclerotic effects through a decrease of net cellular cholesterol content. © 2019 International Society for Advancement of Cytometry.

Diseases Producing Malabsorption and Maldigestion

Malabsorption refers to the impaired intestinal absorption of nutrients. It can result from congenital defects in absorption and the transport of ions and nutrients, defects in hydrolysis within the intestinal lumen, acquired defects in the intestinal absorptive cells that line the surface of the intestine, impaired bile production, or interruption of enterohepatic circulation or secondary to pancreatic insufficiency. Maldigestion, another factor in nutrient absorption, refers to the impaired digestion of nutrients within the intestinal lumen or at the terminal digestive site of the brush border membrane of mucosal epithelial cells. Although malabsorption and maldigestion are pathophysiologically distinct, they are interdependent, and in clinical practice, malabsorption has come to signify derangements in either or both processes. This chapter discusses the clinical manifestations of malabsorption and tests for suspected malabsorption. The diseases that can cause malabsorption, their diagnosis, and treatment recommendations are included. Figures illustrate the diagnosis and management of celiac disease; an approach to gluten challenge for the diagnosis or exclusion of celiac disease in patients maintained on a gluten-free diet without previous definitive diagnostic testing; and the histologic features of celiac disease, Crohn disease, collagenous sprue, autoimmune enteropathy, eosinophilic gastritis, and intestinal lymphangiectasia. This review contains 9 figures, 25 tables, and 116 references. Keywords: Malabsorption, maldigestion, Crohn disease, celiac disease, tropical sprue, diarrhea, endoscopy, short bowel syndrome, bacterial overgrowth

Diseases Producing Malabsorption and Maldigestion

Malabsorption refers to the impaired intestinal absorption of nutrients. It can result from congenital defects in absorption and the transport of ions and nutrients, defects in hydrolysis within the intestinal lumen, acquired defects in the intestinal absorptive cells that line the surface of the intestine, impaired bile production, or interruption of enterohepatic circulation or secondary to pancreatic insufficiency. Maldigestion, another factor in nutrient absorption, refers to the impaired digestion of nutrients within the intestinal lumen or at the terminal digestive site of the brush border membrane of mucosal epithelial cells. Although malabsorption and maldigestion are pathophysiologically distinct, they are interdependent, and in clinical practice, malabsorption has come to signify derangements in either or both processes. This chapter discusses the clinical manifestations of malabsorption and tests for suspected malabsorption. The diseases that can cause malabsorption, their diagnosis, and treatment recommendations are included. Figures illustrate the diagnosis and management of celiac disease; an approach to gluten challenge for the diagnosis or exclusion of celiac disease in patients maintained on a gluten-free diet without previous definitive diagnostic testing; and the histologic features of celiac disease, Crohn disease, collagenous sprue, autoimmune enteropathy, eosinophilic gastritis, and intestinal lymphangiectasia. This review contains 9 figures, 25 tables, and 116 references. Keywords: Malabsorption, maldigestion, Crohn disease, celiac disease, tropical sprue, diarrhea, endoscopy, short bowel syndrome, bacterial overgrowth

Key Facilitator Proteins that Mediate Sarcolemma Membrane Repair have Potential as Therapeutics for Muscle Disease and Injury

A common aspect of many diseases and traumatic injuries affecting skeletal muscle is the necrotic death of muscle fibers. Necrotic death of muscle fibers involves the breakdown of the sarcolemmal membrane that can be exacerbated by increased fragility of the membrane or by compromised endogenous sarcolemmal membrane repair processes. Increasing these repair mechanisms could act as a therapeutic approach for a number of muscle diseases and injuries. Duchenne muscular dystrophy (DMD) is a fatal X‐linked inherited neuromuscular disorder caused by mutations in the dystrophin gene that provides a model for muscle injury and the effects of membrane repair. The dystrophin protein normally serves as a shock absorber for mechanical stress and as a signaling platform protein in muscle fibers. When dystrophin is lacking, patients experience an accumulation of membrane damage that muscle fibers cannot adequately repair. As a result, there is an increase in fiber necrosis that exceeds the regenerative capacity of the muscle. This causes DMD patients to develop striated muscle deterioration that leads to eventual death in the third decade of life. There is currently no cure for DMD and treatments that stimulate the membrane repair process in muscle fibers have been greatly overlooked and underutilized as a potential therapeutic approach. This project investigates a novel membrane repair signaling cascade in skeletal muscle that utilizes glucose storage vesicles (GSVs) and their key regulators Akt Substrate 160 kDa (AS160) and rab G proteins as a means to close membrane wounds. Based on our preliminary data, we hypothesize that AS160 phosphorylation and activation of associating rab G proteins facilitate the translocation of intracellular GSVs to disruption sites in the sarcolemma membrane for wound closure. Thus, modulating the function of these proteins may stimulate repair and have therapeutic benefits for DMD. Through the use of mutant plasmids and live cell imaging, we have observed that GSVs containing the glucose transport protein GLUT4, as well as affiliated rabs, translocate to injury cites in C2C12 myoblasts and isolated mouse muscle fibers. We have also identified that AS160 phosphorylation from the phosphoinositide‐3 kinase (PI3K)/Akt1 signaling axis regulates membrane repair in cultured muscle cells. Importantly, we have screened GSV associating rab G proteins and have found that specific rab proteins are involved in sarcolemma membrane repair in vivo, and that activating rab10 significantly improves membrane resealing in vivo in the muscle of a Duchenne muscular dystrophy mouse model (MDX). This project explores a novel signaling cascade controlling membrane repair that could be leveraged to develop new therapies for muscle disease and injury.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

ATG9A shapes the forming autophagosome through Arfaptin 2 and phosphatidylinositol 4-kinase IIIβ.

ATG9A is a multispanning membrane protein essential for autophagy. Normally resident in Golgi membranes and endosomes, during amino acid starvation, ATG9A traffics to sites of autophagosome formation. ATG9A is not incorporated into autophagosomes but is proposed to supply so-far-unidentified proteins and lipids to the autophagosome. To address this function of ATG9A, a quantitative analysis of ATG9A-positive compartments immunoisolated from amino acid-starved cells was performed. These ATG9A vesicles are depleted of Golgi proteins and enriched in BAR-domain containing proteins, Arfaptins, and phosphoinositide-metabolizing enzymes. Arfaptin2 regulates the starvation-dependent distribution of ATG9A vesicles, and these ATG9A vesicles deliver the PI4-kinase, PI4KIIIβ, to the autophagosome initiation site. PI4KIIIβ interacts with ATG9A and ATG13 to control PI4P production at the initiation membrane site and the autophagic response. PI4KIIIβ and PI4P likely function by recruiting the ULK1/2 initiation kinase complex subunit ATG13 to nascent autophagosomes.