MO441CALPROTECTIN IS A NOVEL CONTRIBUTING FACTOR IN VASCULAR CALCIFICATION AND A PREDICTOR OF CARDIOVASCULAR OUTCOME IN CKD PATIENTS*

Background and Aims

Vascular calcification, leading to aortic stiffening and heart failure, is decisive risk factor for cardiovascular (CV) mortality in patients with chronic kidney disease (CKD). Promoted by bone mineral disorder and systemic inflammation in CKD patients, vascular calcification is a complex mechanism involving osteochondrogenic differentiation of vascular smooth muscle cells (VSMCs) and abnormal deposition of minerals in the vascular wall. Despite intensive research efforts in recent years, available treatments have limited effect and none of them prevent or reverse vascular calcification. The aim of this study was to analyse the serum proteome of CKD stage 3-4 patients in order to unravel new molecular changes associated to CV morbid-mortality and to decipher the role of novel candidates on vascular calcification to provide potential new therapeutic agents.

Method

In this study we used serum samples from two independent cohorts: 112 CKD stage 3-4 patients with a 4 years follow-up for CV events and 222 CKD stage 5 patients exhibiting a broad range of calcification degree determined by histological quantification in the epigastric and/or iliac artery. Serum proteome analysis was performed using tandem mass-spectrometry in a subcohort of 66 CKD3-4 patients and validation of protein candidates was performed using ELISA in the two full cohorts. Human primary vascular smooth muscle cells and mouse aortic rings were used for calcification assays. Calcium content was quantified using QuantiChrom calcium assay kit and calcium deposition was visualized by Alizarin Red and Von Kossa staining.

Results

Among 443 proteins detected in the serum of CKD3-4 patients, 134 displayed significant modified abundance in patients with CV events (n=32) compared to patients without (n=34). One of the most prominent changes was increased level of calprotectin (up to 8.6 fold, P<.0001). Using ELISA, we validated that higher serum calprotectin levels were strongly associated with higher probability of developing CV complications and increased mortality in CKD stage 3-4 patients (Figure A). Moreover, we showed that higher serum calprotectin was associated with increased vascular calcification levels in CKD stage 5 patients (Figure B). In vitro, calprotectin promoted calcification of human VSMCs (p<0.0001) (Figures C-D) and in mouse aortic rings (p<0.0001) (Figure E-F). Interestingly, these effects were significantly attenuated by paquinimod, a calprotectin inhibitor (Figures C-F).

Conclusion

Circulating calprotectin is a novel predictor of CV outcome and mortality in CKD patients. Calprotectin also shows calcification-inducing properties and its blockade by paquinimod alleviates its effects. Future experiments will consist in deciphering the signalling pathways involved in the regulation of calcification by calprotectin and evaluating in vivo the therapeutic potential of paquinimod on the development of medial vascular calcification lesions associated with CKD.

Detection of IgE-reactive proteins in hydrolysed dog foods

BACKGROUND

Commercial hydrolysed diets are used for the diagnosis of food allergy in dogs. The cleaved parent proteins are presumed to be too small to elicit an allergic response by reacting with allergen-specific immunoglobin E (IgE).

OBJECTIVES

To evaluate three commercial hydrolysed dog diets for proteins.

ANIMALS

Sera were collected from dogs with suspected food allergy.

METHODS

Two batches of each hydrolysed diet were examined by electrophoresis and visualized by Coomassie blue, silver nitrate staining and IgE immunoblotting.

RESULTS

From two to five proteins, ranging from 21 to 67 kDa, were detected in all three diets evaluated. Circulating IgE antibodies targeting these proteins were detected by immunoblotting of dog sera. Six different carbohydrate proteins were identified by mass spectrometry; maize/potato granule-bound starch synthase-1, soybean glycinin, soybean β-conglycinin α chain, potato aspartic protease inhibitor, rice glutelin type B1 and soybean sucrose-binding protein. Four of these proteins have been described as allergens in humans.

CONCLUSIONS

Some commercial hydrolysed diets contain carbohydrate proteins. Some dogs have circulating IgE antibodies targeting these proteins. The clinical significance of these findings is unknown.

DNA damage triggers SAF-A and RNA biogenesis factors exclusion from chromatin coupled to R-loops removal

We previously identified the heterogeneous ribonucleoprotein SAF-A/hnRNP U as a substrate for DNA-PK, a protein kinase involved in DNA damage response (DDR). Using laser micro-irradiation in human cells, we report here that SAF-A exhibits a two-phase dynamics at sites of DNA damage, with a rapid and transient recruitment followed by a prolonged exclusion. SAF-A recruitment corresponds to its binding to Poly(ADP-ribose) while its exclusion is dependent on the activity of ATM, ATR and DNA-PK and reflects the dissociation from chromatin of SAF-A associated with ongoing transcription. Having established that SAF-A RNA-binding domain recapitulates SAF-A dynamics, we show that this domain is part of a complex comprising several mRNA biogenesis proteins of which at least two, FUS/TLS and TAFII68/TAF15, exhibit similar biphasic dynamics at sites of damage. Using an original reporter for live imaging of DNA:RNA hybrids (R-loops), we show a transient transcription-dependent accumulation of R-loops at sites of DNA damage that is prolonged upon inhibition of RNA biogenesis factors exclusion. We propose that a new component of the DDR is an active anti-R-loop mechanism operating at damaged transcribed sites which includes the exclusion of mRNA biogenesis factors such as SAF-A, FUS and TAF15.

Structure of the Mesorhizobium huakuii and Rhizobium galegae Nod factors: a cluster of phylogenetically related legumes are nodulated by rhizobia producing Nod factors with alpha,beta-unsaturated N-acyl substitutions

Rhizobia are symbiotic bacteria that synthesize lipochitooligosaccharide Nod factors (NFs), which act as signal molecules in the nodulation of specific legume hosts. Based on the structure of their N-acyl chain, NFs can be classified into two categories: (i) those that are acylated with fatty acids from the general lipid metabolism; and (ii) those (= alphaU-NFs) that are acylated by specific alpha,beta-unsaturated fatty acids (containing carbonyl-conjugated unsaturation(s)). Previous work has described how rhizobia that nodulate legumes of the Trifolieae and Vicieae tribes produce alphaU-NFs. Here, we have studied the structure of NFs from two rhizobial species that nodulate important genera of the Galegeae tribe, related to Trifolieae and Vicieae. Three strains of Mesorhizobium huakuii, symbionts of Astragalus sinicus, produced as major NFs, pentameric lipochitooligosaccharides O-sulphated and partially N-glycolylated at the reducing end and N-acylated, at the non-reducing end, by a C18:4 fatty acid. Two strains of Rhizobium galegae, symbionts of Galega sp., produced as major NFs, tetrameric O-carbamoylated NFs that could be O-acetylated on the glucosamine residue next to the non-reducing terminal glucosamine and were N-acylated by C18 and C20 alpha,beta-unsaturated fatty acids. These results suggest that legumes nodulated by rhizobia synthesizing alphaU-NFs constitute a phylogenetic cluster in the Galegoid phylum.