Jessica Holmén-Larsson

Bacteria penetrate the normally impenetrable inner colon mucus layer in both murine colitis models and patients with ulcerative colitis

Objective The inner mucus layer in mouse colon normally separates bacteria from the epithelium. Do humans have a similar inner mucus layer and are defects in this mucus layer a common denominator for spontaneous colitis in mice models and ulcerative colitis (UC)? Methods and results The colon mucus layer from mice deficient in Muc2 mucin, Core 1 O-glycans, Tlr5, interleukin 10 (IL-10) and Slc9a3 (Nhe3) together with that from dextran sodium sulfate-treated mice was immunostained for Muc2, and bacterial localisation in the mucus was analysed. All murine colitis models revealed bacteria in contact with the epithelium. Additional analysis of the less inflamed IL-10−/− mice revealed a thicker mucus layer than wild-type, but the properties were different, as the inner mucus layer could be penetrated both by bacteria in vivo and by fluorescent beads the size of bacteria ex vivo. Clear separation between bacteria or fluorescent beads and the epithelium mediated by the inner mucus layer was also evident in normal human sigmoid colon biopsy samples. In contrast, mucus on colon biopsy specimens from patients with UC with acute inflammation was highly penetrable. Most patients with UC in remission had an impenetrable mucus layer similar to that of controls. Conclusions Normal human sigmoid colon has an inner mucus layer that is impenetrable to bacteria. The colon mucus in animal models that spontaneously develop colitis and in patients with active UC allows bacteria to penetrate and reach the epithelium. Thus colon mucus properties can be modulated, and this suggests a novel model of UC pathophysiology.

Composition and functional role of the mucus layers in the intestine

In discussions on intestinal protection, the protective capacity of mucus has not been very much considered. The progress in the last years in understanding the molecular nature of mucins, the main building blocks of mucus, has, however, changed this. The intestinal enterocytes have their apical surfaces covered by transmembrane mucins and the whole intestinal surface is further covered by mucus, built around the gel-forming mucin MUC2. The mucus of the small intestine has only one layer, whereas the large intestine has a two-layered mucus where the inner, attached layer has a protective function for the intestine, as it is impermeable to the luminal bacteria.

Normalization of Host Intestinal Mucus Layers Requires Long-Term Microbial Colonization

The intestinal mucus layer provides a barrier limiting bacterial contact with the underlying epithelium. Mucus structure is shaped by intestinal location and the microbiota. To understand how commensals modulate gut mucus, we examined mucus properties under germ-free (GF) conditions and during microbial colonization. Although the colon mucus organization of GF mice was similar to that of conventionally raised (Convr) mice, the GF inner mucus layer was penetrable to bacteria-sized beads. During colonization, in which GF mice were gavaged with Convr microbiota, the small intestine mucus required 5 weeks to be normally detached and colonic inner mucus 6 weeks to become impenetrable. The composition of the small intestinal microbiota during colonization was similar to Convr donors until 3 weeks, when Bacteroides increased, Firmicutes decreased, and segmented filamentous bacteria became undetectable. These findings highlight the dynamics of mucus layer development and indicate that studies of mature microbe-mucus interactions should be conducted weeks after colonization.

Detailed O-glycomics of the Muc2 mucin from colon of wild-type, core 1- and core 3-transferase-deficient mice highlights differences compared with human MUC2

The heavily O-glycosylated mucin MUC2 constitutes the major protein in the mucosal layer that acts as a physical barrier protecting the epithelial layer in the colon. In this study, Muc2 was purified from mucosal scrapings from the colon of wild-type (WT) mice, core 3 transferase knockout (C3Gnt(-/-)) mice and intestinal epithelial cell-specific core 1 knockout (IEC C1Galt1(-/-)) mice. The Muc2 O-glycans were released by reductive β-elimination and analyzed with liquid chromatography-mass spectrometry in the negative-ion mode. Muc2 from the distal colon of WT and C3Gnt(-/-) knockout mice carried a mixture of core 1- or core 2-type glycans, whereas Muc2 from IEC C1Galt1(-/-) mice carried highly sialylated core 3- and core 4-type glycans. A large portion of NeuAc in all mouse models was positioned on disialylated N-acetyllactosamine units, an epitope not reported on human colonic MUC2. Mass spectra and proton NMR spectroscopy revealed an abundant NeuAc linked to internally positioned N-acetylglucosamine on colonic murine Muc2, which also differs markedly from human MUC2. Our results highlight that murine colonic Muc2 O-glycosylation is substantially different from human MUC2, which could be one explanation for the different commensal microbiota of these two species.

An Integrated Workflow for Multiplex CSF Proteomics and Peptidomics-Identification of Candidate Cerebrospinal Fluid Biomarkers of Alzheimer's Disease

Many disease processes in the brain are reflected in the protein composition of the cerebrospinal fluid (CSF). In addition to proteins, CSF also contains a large number of endogenous peptides whose potential as disease biomarkers largely remains to be explored. We have developed a novel workflow in which multiplex isobaric labeling is used for simultaneous quantification of endogenous CSF peptides and proteins by liquid chromatography coupled with mass spectrometry. After the labeling of CSF samples, endogenous peptides are separated from proteins by ultrafiltration. The proteins retained on the filters are trypsinized, and the tryptic peptides are collected separately. We evaluated this technique in a comparative pilot study of CSF peptide and protein profiles in eight patients with Alzheimers disease (AD) and eight nondemented controls. We identified several differences between the AD and control group among endogenous peptides derived from proteins known to be associated with AD, including neurosecretory protein VGF (ratios AD/controls 0.45-0.81), integral membrane protein 2B (ratios AD/controls 0.72-0.84), and metallothionein-3 (ratios AD/controls 0.51-0.61). Analysis of tryptic peptides identified several proteins that were altered in the AD group, some of which have previously been reported as changed in AD, for example, VGF (ratio AD/controls 0.70).

Blood metabolomics analysis identifies abnormalities in the citric acid cycle, urea cycle, and amino acid metabolism in bipolar disorder

Background Bipolar disorder (BD) is a severe and debilitating psychiatric disorder. However, the precise biological basis remains unknown, hampering the search for novel biomarkers. We performed a metabolomics analysis to discover novel peripheral biomarkers for BD. Methods We quantified serum levels of 116 metabolites in mood-stabilized male BD patients (n = 54) and age-matched male healthy controls (n = 39). Results After multivariate logistic regression, serum levels of pyruvate, N-acetylglutamic acid, α-ketoglutarate, and arginine were significantly higher in BD patients than in healthy controls. Conversely, serum levels of β-alanine, and serine were significantly lower in BD patients than in healthy controls. Chronic (4-weeks) administration of lithium or valproic acid to adult male rats did not alter serum levels of pyruvate, N-acetylglutamic acid, β-alanine, serine, or arginine, but lithium administration significantly increased serum levels of α-ketoglutarate. Conclusions The metabolomics analysis demonstrated altered serum levels of pyruvate, N-acetylglutamic acid, β-alanine, serine, and arginine in BD patients. General significance The present findings suggest that abnormalities in the citric acid cycle, urea cycle, and amino acid metabolism play a role in the pathogenesis of BD.

Expanding the cerebrospinal fluid endopeptidome

Biomarkers of neurodegenerative disorders are needed to assist in diagnosis, to monitor disease progression and therapeutic interventions, and to provide insight into disease mechanisms. One route to identify such biomarkers is by proteomic and peptidomic analysis of cerebrospinal fluid (CSF). In the current study, we performed an in‐depth analysis of the human CSF endopeptidome to establish an inventory that may serve as a basis for future targeted biomarker studies. High‐pH RP HPLC was employed for off‐line sample prefractionation followed by low‐pH nano‐LC‐MS analysis. Different software programs and scoring algorithms for peptide identification were employed and compared. A total of 18 031 endogenous peptides were identified at a FDR of 1%, increasing the number of known endogenous CSF peptides 10‐fold compared to previous studies. The peptides were derived from 2 053 proteins of which more than 60 have been linked to neurodegeneration. Notably, among the findings were six peptides derived from microtubule‐associated protein tau, three of which span the diagnostically interesting threonine‐181 (Tau‐F isoform). Also, 213 peptides from amyloid precursor protein were identified, 58 of which were partially or completely within the sequence of amyloid β 1–40/42, as well as 109 peptides from apolipoprotein E, spanning sequences that discriminate between the E2/E3/E4 isoforms of the protein.

Intestinal Muc2 mucin O-glycosylation is affected by microbiota and regulated by differential expression of glycosyltranferases

Intestinal cells are covered by mucus. In the small intestine, a single unattached mucus is present whereas the colon has both an inner attached mucus layer and an outer loose mucus. The attached mucus of the colon is impenetrable to bacteria while the loose mucus acts as a habitat for commensal bacteria. In germ-free (GF) mice, small intestinal mucus is attached to the epithelium and the inner colon mucus is penetrable. O-glycosylation plays an important role in the host-microbiota interactions as the commensal bacteria use glycans as nutrient sources and attachment sites. While mucus protein composition is relatively homogenous along the intestine, its main component the Muc2 mucin shows regiospecific O-glycan patterns. We have now analyzed the glycosyltransferase relative concentrations in the epithelial cells along the intestine in GF and conventionally raised mice and compared this with the O-glycans formed. As Muc2 is the main O-glycosylated product in mucus, we made the simplified assumption that most of the glycosyltransferases found in the epithelial cells are involved in Muc2 O-glycan biosynthesis. The O-glycosyltransferase abundances along the intestine correlated well with the Muc2 O-glycan patterns. Some of the glycosyltransferases involved in the O-glycan elongation were decreased in GF mice, something that is in concordance with the observed shorter Muc2 O-glycans.

Markers of neuroinflammation and neuronal injury in bipolar disorder: Relation to prospective clinical outcomes

Neuroimmune mechanisms have been linked to the pathophysiology of bipolar disorder based on studies of biomarkers in plasma, cerebrospinal fluid (CSF), and postmortem brain tissue. There are, however, no longitudinal studies investigating if CSF markers of neuroinflammation and neuronal injury predict clinical outcomes in patients with bipolar disorder. We have in previous studies found higher CSF concentrations of interleukin-8 (IL-8), monocyte chemoattractant protein 1 (MCP-1/CCL-2), chitinase-3-like protein 1 (CHI3L1/YKL-40), and neurofilament light chain (NF-L) in euthymic patients with bipolar disorder compared with controls. Here, we investigated the relationship of these CSF markers of neuroinflammation and neuronal injury with clinical outcomes in a prospective study. 77 patients with CSF analyzed at baseline were followed for 6-7years. Associations of baseline biomarkers with clinical outcomes (manic/hypomanic and depressive episodes, suicide attempts, psychotic symptoms, inpatient care, GAF score change) were investigated. Baseline MCP-1 concentrations were positively associated with manic/hypomanic episodes and inpatient care during follow-up. YKL-40 concentrations were negatively associated with manic/hypomanic episodes and with occurrence of psychotic symptoms. The prospective negative association between YKL-40 and manic/hypomanic episodes survived multiple testing correction. Concentrations of IL-8 and NF-L were not associated with clinical outcomes. High concentrations of these selected CSF markers of neuroinflammation and neuronal injury at baseline were not consistently associated with poor clinical outcomes in this prospective study. The assessed proteins may be involved in adaptive immune processes or reflect a state of vulnerability for bipolar disorder rather than being of predictive value for disease progression.

Sample Preparation for Endopeptidomic Analysis in Human Cerebrospinal Fluid

This protocol describes a method developed to identify endogenous peptides in human cerebrospinal fluid (CSF). For this purpose, a previously developed method based on molecular weight cut-off (MWCO) filtration and mass spectrometric analysis was combined with an offline high-pH reverse phase HPLC pre-fractionation step. Secretion into CSF is the main pathway for removal of molecules shed by cells of the central nervous system. Thus, many processes in the central nervous system are reflected in the CSF, rendering it a valuable diagnostic fluid. CSF has a complex composition, containing proteins that span a concentration range of 8 - 9 orders of magnitude. Besides proteins, previous studies have also demonstrated the presence of a large number of endogenous peptides. While less extensively studied than proteins, these may also hold potential interest as biomarkers. Endogenous peptides were separated from the CSF protein content through MWCO filtration. By removing a majority of the protein content from the sample, it is possible to increase the sample volume studied and thereby also the total amount of the endogenous peptides. The complexity of the filtrated peptide mixture was addressed by including a reverse phase (RP) HPLC pre-fractionation step at alkaline pH prior to LC-MS analysis. The fractionation was combined with a simple concatenation scheme where 60 fractions were pooled into 12, analysis time consumption could thereby be reduced while still largely avoiding co-elution. Automated peptide identification was performed by using three different peptide/protein identification software programs and subsequently combining the results. The different programs were complementary rather than comparable with less than 15% of the identifications overlapped between the three.