Cécile Caubet

Refined Characterization of Corneodesmosin Proteolysis during Terminal Differentiation of Human Epidermis and Its Relationship to Desquamation

Corneodesmosin is a putative adhesion glycoprotein located in the extracellular part of the desmosomes in the upper layers of the epidermis. Synthesized by granular keratinocytes as a 52–56-kDa protein, corneodesmosin is progressively proteolysed during corneocyte maturation. This processing is a prerequisite for desquamation. Two glycine- and serine-rich domains of the protein might take on the conformation of adhesive secondary structures similar to glycine loops. Corneodesmosin proteolysis was further characterized. Deglycosylation experiments and reactivity with lectins demonstrated that the corneodesmosin carbohydrate moiety does not prevent the proteolysis. Immunoblotting, immunohistochemistry, and immunoelectron microscopy experiments using affinity-purified anti-peptide antibodies raised to four of the five structural domains of corneodesmosin and a monoclonal antibody against its fifth central domain showed that the first step in corneodesmosin processing is the cleavage of its extremities and probably occurs before its incorporation into desmosomes. Then the glycine loop-related domains are cleaved, first the N-terminal and then part of the C-terminal domain. At the epidermis surface, the multistep proteolytic cleavage leaves intact only the central domain, which was detected on exfoliated corneocytes and probably lacks adhesive properties. Importantly, corneodesmosin was demonstrated to be a preferred substrate of two serine proteases involved in desquamation, the stratum corneum tryptic and chymotryptic enzymes.

Secretory IgA-mediated neutralization of Shigella flexneri prevents intestinal tissue destruction by down-regulating inflammatory circuits.

Shigella, a Gram-negative invasive enteropathogenic bacterium responsible for bacillary dysentery, causes the rupture, invasion, and inflammatory destruction of the human colonic mucosa. We explored the mechanisms of protection mediated by Shigella LPS-specific secretory IgA (SIgA), the major mucosal Ab induced upon natural infection. Bacteria, SIgA, or SIgA-S. flexneri immune complexes were administered into rabbit ligated intestinal loops containing a Peyer’s patch. After 8 h, localizations of bacteria, SIgA, and SIgA-S. flexneri immune complexes were examined by immunohistochemistry and confocal microscopy imaging. We found that anti-Shigella LPS SIgA, mainly via immune exclusion, prevented Shigella-induced inflammation responsible for the destruction of the intestinal barrier. Besides this luminal trapping, a small proportion of SIgA-S. flexneri immune complexes were shown to enter the rabbit Peyer’s patch and were internalized by dendritic cells of the subepithelial dome region. Local inflammatory status was analyzed by quantitative RT-PCR using newly designed primers for rabbit pro- and anti-inflammatory mediator genes. In Peyer’s patches exposed to immune complexes, limited up-regulation of the expression of proinflammatory genes, including TNF-α, IL-6, Cox-2, and IFN-γ, was observed, consistent with preserved morphology. In contrast, in Peyer’s patches exposed to Shigella alone, high expression of the same mediators was measured, indicating that neutralizing SIgA dampens the proinflammatory properties of Shigella. These results show that in the form of immune complexes, SIgA guarantees both immune exclusion and neutralization of translocated bacteria, thus preserving the intestinal barrier integrity by preventing bacterial-induced inflammation. These findings add to the multiple facets of the noninflammatory properties of SIgA.

Corneodesmosin, a Component of Epidermal Corneocyte Desmosomes, Displays Homophilic Adhesive Properties

Corneodesmosomes, the modified desmosomes of the uppermost layers of the epidermis, play an important role in corneocyte cohesion. Corneodesmosin is a secreted glycoprotein located in the corneodesmosomal core and covalently linked to the cornified envelope of corneocytes. Its glycine- and serine-rich NH2-terminal domain may fold to give structural motifs similar to the glycine loops described in epidermal cytokeratins and loricrin and proposed to display adhesive properties. A chimeric protein comprising human corneodesmosin linked to the transmembrane and cytoplasmic domains of mouse E-cadherin was expressed in mouse fibroblasts to test the ability of corneodesmosin to promote cell-cell adhesion. Classic aggregation assays indicated that corneodesmosin mediates homophilic cell aggregation. Moreover, Ca2+depletion showed a moderate effect on aggregation. To assess the involvement of the glycine loop domain in adhesion, full-length corneodesmosin, corneodesmosin lacking this domain, or this domain alone were expressed as glutathione S-transferase fusion proteins and tested for protein-protein interactions by overlay binding assays. The results confirmed that corneodesmosin presents homophilic interactions and indicated that its NH2-terminal glycine loop domain is sufficient but not strictly necessary to promote binding. Altogether, these results provide the first experimental evidence for the adhesive properties of corneodesmosin and for the involvement of its glycine loop domain in adhesion.

Advances in urinary proteome analysis and biomarker discovery in pediatric renal disease

Recent progress in proteomic analysis and strategies for the identification of clinically useful biomarkers in biofluids has led to the identification of urine as an excellent non-invasive reservoir for biomarkers of disease. Urinary biomarkers have been identified and validated on independent cohorts in different high-incidence adult renal diseases, including diabetic nephropathy, chronic kidney disease and immunoglobulin A-nephropathy, but also in extrarenal disease, such as coronary artery disease. Unfortunately, this type of research is underrepresented in the pediatric population. Here, we present the rare studies in the pediatric population that identified potential clinically useful urinary biomarkers in ureteropelvic junction (UPJ) obstruction and renal Fanconi syndrome. These studies, although limited in number, clearly show the potential of urinary proteomics, especially in the pediatric population. It is anticipated that the advances made in the adult population, the lessons learned on the use of appropriate statistics and the inclusion of independent blinded validation cohorts in these types of studies will rapidly lead to clinical useful urinary biomarkers for other pediatric (renal) disease in a population where non-invasive analysis is particularly appreciated.

Fetal Urinary Peptides to Predict Postnatal Outcome of Renal Disease in Fetuses with Posterior Urethral Valves (PUV)

Peptides found in fetal urine predict end-stage renal disease in patients with a congenital abnormality of the kidney and urinary tract. Seeking a Signature of Renal Disease Being able to predict—in utero—whether a fetus will have severe kidney disease would help anxious parents make informed treatment decisions earlier. To this end, Klein and colleagues searched through thousands of peptides in fetal urine to find potential markers of end-stage renal disease (ESRD). The authors obtained urine samples from fetuses with posterior urethral valves (PUV), which is an abnormality of the urinary tract that can lead to ESRD. They knew the outcome of these patients with PUV, that is, whether or not they had ESRD before the age of 2. Out of >4000 peptides, Klein et al. identified a handful that were linked to ESRD, but were not present in the fetal urine of patients who did not progress to ESRD. In an independent set of samples, this peptide-based signature, called 12PUV, was similarly able to predict postnatal renal function, outperforming routine clinical procedures such as ultrasound and biochemical tests. Although many more fetal urine samples are needed for validation, this peptide-based predictor shows promise as a much needed test to help clinicians and families make prenatal treatment decisions for fetuses with PUV. Bilateral congenital abnormalities of the kidney and urinary tract (CAKUT), although are individually rare diseases, remain the main cause of chronic kidney disease in infants worldwide. Bilateral CAKUT display a wide spectrum of pre- and postnatal outcomes ranging from death in utero to normal postnatal renal function. Methods to predict these outcomes in utero are controversial and, in several cases, lead to unjustified termination of pregnancy. Using capillary electrophoresis coupled with mass spectrometry, we have analyzed the urinary proteome of fetuses with posterior urethral valves (PUV), the prototypic bilateral CAKUT, for the presence of biomarkers predicting postnatal renal function. Among more than 4000 fetal urinary peptide candidates, 26 peptides were identified that were specifically associated with PUV in 13 patients with early end-stage renal disease (ESRD) compared to 15 patients with absence of ESRD before the age of 2. A classifier based on these peptides correctly predicted postnatal renal function with 88% sensitivity and 95% specificity in an independent blinded validation cohort of 38 PUV patients, outperforming classical methods, including fetal urine biochemistry and fetal ultrasound. This study demonstrates that fetal urine is an important pool of peptides that can predict postnatal renal function and thus be used to make clinical decisions regarding pregnancy.

Congenital ureteropelvic junction obstruction: human disease and animal models

Ureteropelvic junction (UPJ) obstruction is the most frequently observed cause of obstructive nephropathy in children. Neonatal and foetal animal models have been developed that mimic closely what is observed in human disease. The purpose of this review is to discuss how obstructive nephropathy alters kidney histology and function and describe the molecular mechanisms involved in the progression of the lesions, including inflammation, proliferation/apoptosis, renin–angiotensin system activation and fibrosis, based on both human and animal data. Also we propose that during obstructive nephropathy, hydrodynamic modifications are early inducers of the tubular lesions, which are potentially at the origin of the pathology. Finally, an important observation in animal models is that relief of obstruction during kidney development has important effects on renal function later in adult life. A major short‐coming is the absence of data on the impact of UPJ obstruction on long‐term adult renal function to elucidate whether these animal data are also valid in humans.

Corneodesmosomes and corneodesmosin: from the stratum corneum cohesion to the pathophysiology of genodermatoses

Corneodesmosin (CDSN) was identified 20 years ago by raising monoclonal antibodies against human plantar stratum corneum. The protein is specific to corneodesmosomes, cell-junction structures that, in humans, are found in the epidermis, the hard palate epithelium, and the inner root sheath of the hair follicles. Synthesized by the granular keratinocytes and secreted via the lamellar bodies, CDSN is incorporated into the desmoglea of the desmosomes, shortly before their transformation into corneodesmosomes during cornification. CDSN displays adhesive properties, mostly attributable to its N-terminal glycine-rich domain, and is sequentially proteolyzed as corneocytes migrate towards the skin surface prior to desquamation. The recent inactivation of Cdsn in mice induced a lethal epidermal barrier disruption and hair follicle degeneration, related to corneodesmosome dysfunction. That confirmed the essential role of the protein in maintaining integrity of the epidermis and the hair follicle. The CDSN gene is located in PSORS1, the major psoriasis susceptibility locus on the chromosome 6, but to date its involvement in the disease pathophysiology is not clear. By contrast, two different monogenic diseases associated with nonsense mutations in CDSN, were recently identified. First, hypotrichosis simplex of the scalp in which mutated CDSN accumulates in the dermis and forms amyloid deposits; then, peeling skin disease in which the genetic defect induces dyscohesion of the stratum corneum, responsible for abnormal desquamation and increased skin penetration of allergens.

Maternal Milk Contains Antimicrobial Factors That Protect Young Rabbits from Enteropathogenic Escherichia coli Infection

ABSTRACT Enteropathogenic Escherichia coli (EPEC) colibacillosis represents a major cause of lethal diarrhea in young children in developing countries. EPEC strains also infect numerous mammal species and represent a major economical problem in rabbit industry. Protection against this pathogen is a challenging goal both in humans and in other mammal species. Despite a good knowledge of the pathogenicity mechanisms of EPEC, the intrinsic and environmental factors that control the expression of EPEC virulence in mammals remain unknown. For instance, the exacerbated sensitivity of young mammals to EPEC infection is still unexplained. Our goal was to investigate if age or other factors, like milk consumption, could be determinants that trigger the disease. We used rabbits as an animal model to study the role of milk in the sensitivity to an EPEC infection. Weaned and suckling rabbits were orally inoculated with EPEC strain E22 (O103:H2:K−) at 28 days of age, and the evolution of the disease was investigated in the two groups. In addition, in order to better characterize the interactions between milk and EPEC, we determined in vitro bacterial growth and the abilities of EPEC cells to adhere to epithelial cells in the presence of milk. Our results demonstrate a protective role of milk in vivo in association with in vitro antibacterial activity. These effects are independent of the presence of specific anti-EPEC antibodies.

Long Term Metabolic Syndrome Induced by a High Fat High Fructose Diet Leads to Minimal Renal Injury in C57BL/6 Mice

Metabolic syndrome can induce chronic kidney disease in humans. Genetically engineered mice on a C57BL/6 background are highly used for mechanistic studies. Although it has been shown that metabolic syndrome induces cardiovascular lesions in C57BL/6 mice, in depth renal phenotyping has never been performed. Therefore in this study we characterized renal function and injury in C57BL/6 mice with long-term metabolic syndrome induced by a high fat and fructose diet (HFFD). C57BL/6 mice received an 8 months HFFD diet enriched with fat (45% energy from fat) and drinking water enriched with fructose (30%). Body weight, food/water consumption, energy intake, fat/lean mass ratio, plasma glucose, HDL, LDL, triglycerides and cholesterol levels were monitored. At 3, 6 and 8 months, renal function was determined by inulin clearance and measure of albuminuria. At sacrifice, kidneys and liver were collected. Metabolic syndrome in C57BL/6 mice fed a HFFD was observed as early 4 weeks with development of type 2 diabetes at 8 weeks after initiation of diet. However, detailed analysis of kidney structure and function showed only minimal renal injury after 8 months of HFFD. HFFD induced moderate glomerular hyperfiltration (436,4 µL/min vs 289,8 µL/min; p-value=0.0418) together with a 2-fold increase in albuminuria only after 8 months of HFFD. This was accompanied by a 2-fold increase in renal inflammation (p-value=0.0217) but without renal fibrosis or mesangial matrix expansion. In addition, electron microscopy did not show alterations in glomeruli such as basal membrane thickening and foot process effacement. Finally, comparison of the urinary peptidome of these mice with the urinary peptidome from humans with diabetic nephropathy also suggested absence of diabetic nephropathy in this model. This study provides evidence that the HFFD C57BL/6 model is not the optimal model to study the effects of metabolic syndrome on the development of diabetic kidney disease.

Alterations in the desquamation-related proteolytic cleavage of corneodesmosin and other corneodesmosomal proteins in psoriatic lesional epidermis.

Background  Desquamation occurs after proteolysis of corneodesmosomal proteins, including corneodesmosin (CDSN), by proteases of the kallikrein family, particularly KLK7. Impaired desquamation is one of the features of psoriasis, and psoriasis‐associated single nucleotide polymorphisms of the CDSN gene may potentially modify the proteolysis of the encoded protein.