Discovery and Targeted Proteomics on Cutaneous Biopsies Infected by Borrelia to Investigate Lyme Disease

Lyme disease is the most important vector-borne disease in the Northern hemisphere and represents a major public health challenge with insufficient means of reliable diagnosis. Skin is rarely investigated in proteomics but constitutes in the case of Lyme disease the key interface where the pathogens can enter, persist, and multiply. Therefore, we investigated proteomics on skin samples to detect Borrelia proteins directly in cutaneous biopsies in a robust and specific way. We first set up a discovery gel prefractionation-LC-MS/MS approach on a murine model infected by Borrelia burgdorferi sensu stricto that allowed the identification of 25 Borrelia proteins among more than 1300 mouse proteins. Then we developed a targeted gel prefractionation-LC-selected reaction monitoring (SRM) assay to detect 9/33 Borrelia proteins/peptides in mouse skin tissue samples using heavy labeled synthetic peptides. We successfully transferred this assay from the mouse model to human skin biopsies (naturally infected by Borrelia), and we were able to detect two Borrelia proteins: OspC and flagellin. Considering the extreme variability of OspC, we developed an extended SRM assay to target a large set of variants. This assay afforded the detection of nine peptides belonging to either OspC or flagellin in human skin biopsies. We further shortened the sample preparation and showed that Borrelia is detectable in mouse and human skin biopsies by directly using a liquid digestion followed by LC-SRM analysis without any prefractionation. This study thus shows that a targeted SRM approach is a promising tool for the early direct diagnosis of Lyme disease with high sensitivity (<10 fmol of OspC/mg of human skin biopsy).Lyme borreliosis is an arthropod-borne disease transmitted by hard ticks (Ixodes spp.). The causative agents are bacteria belonging to the Borrelia burgdorferi sensu lato group. In the United States, more than 30,000 cases have been reported to the Centers for Disease Control and Prevention in 2012. There, the unique pathogenic species of Borrelia is B. burgdorferi sensu stricto (s.s.). In Europe, between 65,000 and 85,000 cases are reported depending on the epidemiological study (1, 2), and the three most prevalent pathogenic species of Borrelia are Borrelia afzelii, Borrelia garinii, and B. burgdorferi s.s. The disease in both Europe and the United States is first characterized in most patients by an inflammatory skin lesion, erythema migrans (EM),¹ which is the most frequent manifestation of the disease. Dissemination to other sites occurs secondarily and can involve among others articulation, nervous system, heart, and skin at other sites (3, 4). The diagnosis can be a real challenge because of the proteiform clinical manifestations. When an EM is present, which is the case for 80% of patients (3), early diagnosis is facilitated. However, EM presentation can be clinically atypical, making the recognition of this manifestation of Lyme borreliosis difficult (5). Later on, when Borrelia has disseminated to the target organs, biological diagnosis is based either on the direct detection of the pathogen in different patient body fluids and biopsies by means of culture and/or PCR or on the indirect demonstration of presence of Borrelia by detection of anti-pathogen-directed IgM and IgG antibodies (enzyme-linked immunosorbent assay (ELISA) and Western blot) (6).Concerning the direct detection of Borrelia, culture of the bacteria has allowed the spirochete isolation since the 80s in different specific Barbour-Stoenner-Kelly-based media by using skin biopsies or biological fluids such as blood or cerebrospinal fluid (7, 8). However, Borrelia culture is not routinely used as a diagnostic test because the bacterial growth takes several weeks and does not yield timely results. Indeed, it requires the use of the specific and expensive Barbour-Stoenner-Kelly medium and a dark field microscope to detect, frequently after at least 2 weeks of incubation, the presence of Borrelia in tissues or biological fluids. When performed from patients with EM, only 40–80% of the cultures are positive (6). In addition, the success of culture varies greatly according to the Borrelia species. PCR is quicker and generally more sensitive than culture with a range of 36–88%, although the success of bacterial detection varies with the gene selected for the assay (6). PCR is efficient for Borrelia detection in synovial liquid (60–85% of the cases) in the case of arthritis (9, 10) but less sensitive in cases of neuroborreliosis in cerebrospinal fluid (<20–40% of the cases) (9, 11). Moreover, PCR detects DNA and not proteins and therefore prevents the detection of active infection. As far as the skin biopsies are concerned, the sensitivity of detection is variable in cases of EM or acrodermatitis chronica atrophicans (12). Conversely, indirect detection using serological tests is not adapted to the early diagnosis as it relies on antibodies only detectable after at least 4–6 weeks after the infectious tick bite. These tests also suffer from lack of specificity (13). New diagnostic approaches are therefore required. Selected reaction monitoring (SRM) has been recognized as an efficient mass spectrometry-based technique for the biomarker verification and validation in several biological fluids (blood, plasma, and urine) (14 –18). The demonstrated specificity, selectivity, and high sensitivity (low attomole range) of the technique (19) makes it promising for the development of an SRM-based method for early diagnosis of Lyme disease. To our knowledge, this strategy has only rarely been used on skin tissue (20). It would allow the direct and rapid detection of Borrelia proteins in the skin, demonstrating the presence of an active infection very early after the tick transmission.In the present study, we set up a workflow to develop a robust and sensitive SRM assay to detect Borrelia in human skin samples (Fig. 1). First, we looked for Borrelia proteins in infected mouse skin samples by using a classical shotgun/discovery strategy. This experiment afforded a list of bacterial proteins that are expressed in vivo in the skin of an infected mammalian host. Then, we selected protein targets and optimized a Ge-LC-SRM assay to specifically detect and quantify these proteins in mouse skin samples. We demonstrated the transferability of the SRM assay for the detection of the targeted proteins in human skin samples naturally infected with Borrelia. Finally, we improved the experimental protocol to avoid gel prefractionation.Open in a separate windowFig. 1.Summary of the experimental workflow. Experimentally infected mouse skin biopsies were analyzed by a shotgun Ge-LC-MS/MS strategy to identify Borrelia target proteins. Then we developed targeted LC-SRM assays with or without gel prefractionation. Finally, these targeted methods were transferred on tick-infected human skin samples.     

Is There a Link between Exertional Heat Stroke and Susceptibility to Malignant Hyperthermia?

Objective

The identification of a predisposition toward malignant hyperthermia (MH) as a risk factor for exertional heat stroke (EHS) remains a matter of debate. Such a predisposition indicates a causal role for MH susceptibility (MHS) after EHS in certain national recommendations and has led to the use of an in vitro contracture test (IVCT) to identify the MHS trait in selected or unselected EHS patients. The aim of this study was to determine whether the MHS trait is associated with EHS.

Methods

EHS subjects in the French Armed Forces were routinely examined for MHS after experiencing an EHS episode. This retrospective study compared the features of IVCT-diagnosed MHS (iMHS) EHS subjects with those of MH-normal EHS patients and MH patients during the 2004–2010 period. MHS status was assessed using the European protocol.

Results

During the study period, 466 subjects (median age 25 years; 31 women) underwent MHS status investigation following an EHS episode. None of the subjects reported previous MH events. An IVCT was performed in 454 cases and was diagnostic of MHS in 45.6% of the study population, of MH susceptibility to halothane in 18.5%, of MH susceptibility to caffeine in 9.9%, and of MH susceptibility to halothane and caffeine in 17.2%. There were no differences in the clinical features, biological features or outcomes of iMHS EHS subjects compared with those of MH-normal or caffeine or halothane MHS subjects without known prior EHS episode. The recurrence rate was 12.7% and was not associated with MH status or any clinical or biological features. iMHS EHS patients exhibited a significantly less informative IVCT response than MH patients.

Conclusions

The unexpected high prevalence of the MHS trait after EHS suggested a latent disturbance of calcium homeostasis that accounted for the positive IVCT results. This study did not determine whether EHS patients have an increased risk of MH, and it could not determine whether MH susceptibility is a risk factor for EHS.     

Phenotypic switch of smooth muscle cells in paediatric chronic intestinal pseudo-obstruction syndrome

Smooth Muscle Cells (SMC) are unique amongst all muscle cells in their capacity to modulate their phenotype. Indeed, SMCs do not terminally differentiate but instead harbour a remarkable capacity to dedifferentiate, switching between a quiescent contractile state and a highly proliferative and migratory phenotype, a quality often associated to SMC dysfunction. However, phenotypic plasticity remains poorly examined in the field of gastroenterology in particular in pathologies in which gut motor activity is impaired. Here, we assessed SMC status in biopsies of infants with chronic intestinal pseudo-obstruction (CIPO) syndrome, a life-threatening intestinal motility disorder. We showed that CIPO-SMCs harbour a decreased level of contractile markers. This phenotype is accompanied by an increase in Platelet-Derived Growth Factor Receptor-alpha (PDGFRA) expression. We showed that this modulation occurs without origin-related differences in CIPO circular and longitudinal-derived SMCs. As we characterized PDGFRA as a marker of digestive mesenchymal progenitors during embryogenesis, our results suggest a phenotypic switch of the CIPO-SMC towards an undifferentiated stage. The development of CIPO-SMC culture and the characterization of SMC phenotypic switch should enable us to design therapeutic approaches to promote SMC differentiation in CIPO.     

Portal sensing of intestinal gluconeogenesis is a mechanistic link in the diminution of food intake induced by diet protein

Protein feeding is known to decrease hunger and subsequent food intake in animals and humans. It has also been suggested that glucose appearance into portal vein, as occurring during meal assimilation, may induce comparable effects. Here, we connect these previous observations by reporting that intestinal gluconeogenesis (i.e., de novo synthesis of glucose) is induced during the postabsorptive time (following food digestion) in rats specifically fed on protein-enriched diet. This results in glucose release into portal blood, counterbalancing the lowering of glycemia resulting from intestinal glucose utilization. Comparable infusions into the portal vein of control postabsorptive rats (fed on starch-enriched diet) decrease food consumption and activate the hypothalamic nuclei regulating food intake. Similar hypothalamic activation occurs on protein feeding. All these effects are absent after denervation of the portal vein. Thus, portal sensing of intestinal gluconeogenesis may be a novel mechanism connecting the macronutrient composition of diet to food intake.     

Yeast cytochrome c oxidase: a model system to study mitochondrial forms of the haem-copper oxidase superfamily

The known subunits of yeast mitochondrial cytochrome c oxidase are reviewed. The structures of all eleven of its subunits are explored by building homology models based on the published structures of the homologous bovine subunits and similarities and differences are highlighted, particularly of the core functional subunit I. Yeast genetic techniques to enable introduction of mutations into the three core mitochondrially-encoded subunits are reviewed.     

New insights into the organisation and intracellular localisation of the two subunits of glucose-6-phosphatase

Glucose-6 phosphatase (G6Pase), a key enzyme of glucose homeostasis, catalyses the hydrolysis of glucose-6 phosphate (G6P) to glucose and inorganic phosphate. A deficiency in G6Pase activity causes type 1 glycogen storage disease (GSD-1), mainly characterised by hypoglycaemia. Genetic analyses of the two forms of this rare disease have shown that the G6Pase system consists of two proteins, a catalytic subunit (G6PC) responsible for GSD-1a, and a G6P translocase (G6PT), responsible for GSD-1b. However, since their identification, few investigations concerning their structural relationship have been made. In this study, we investigated the localisation and membrane organisation of the G6Pase complex. To this aim, we developed chimera proteins by adding a fluorescent protein to the C-terminal ends of both subunits. The G6PC and G6PT fluorescent chimeras were both addressed to perinuclear membranes as previously suggested, but also to vesicles throughout the cytoplasm. We demonstrated that both proteins strongly colocalised in perinuclear membranes. Then, we studied G6PT organisation in the membrane. We highlighted FRET between the labelled C and N termini of G6PT. The intramolecular FRET of this G6PT chimera was 27%. The coexpression of unlabelled G6PC did not modify this FRET intensity. Finally, the chimera constructs generated in this work enabled us for the first time to analyze the relationship between GSD-1 mutations and the intracellular localisation of both G6Pase subunits. We showed that GSD1 mutations did neither alter the G6PC or G6PT chimera localisation, nor the interaction between G6PT termini. In conclusion, our results provide novel information on the intracellular distribution and organisation of the G6Pase complex.