Muscle Wasting in Hemodialysis Patient

Hypothesis Measuring urinary 3-methylhistidine is a simple tool to assess proteolysis in clinical practice. However it is not totally specific of muscle proteolysis because it may reflect an intestinal catabolism. Moreover, its dosage cannot be used in patients with renal impairment especially in case of anuria. Apart from achieving muscle biopsy or measuring the overall kinetics of proteins it does not yet exist simple and reproducible diagnostic tool for measuring muscle proteolysis. With the present study, the investigators expect to identify in the blood of patients a particular transcriptomic profile related to the activation of muscle proteolysis, including increased proinflammatory cytokine transcripts.

Rodent models of CKD were used to identify major proteolytic system and signal pathway implicated in muscle wasting caused by uremia. These finding needs to be confirmed in humans studies. Also, other actors of muscle atrophy could be identified in humans. Notably, so far, few studies have been performed in order to determine which E2 are involved in muscle atrophy, and to knowledge of the investigators no one in CKD. Finally, data on muscle proteasome substrates are limited since only actin was clearly identified in humans by the team. The investigators expect an activation of the proteasome system with an increase in the expression of enzymes E2s, E3s including MURF1 and MAFbx and proteasome subunit in patients treated with hemodialysis. The investigators could also observe an activation of caspase system which is thought to work in concert with the UPS.

Materials and methods 2.1. Population The experiments will be performed using blood sample and human muscle biopsies obtained during programmed orthopedic surgery (negative control), cancer (positive control) and hemodialysis patients. This translational research program has already been accepted (DGS 2008-A00479-46) and inclusion of patients already started. A maximum of 15 patients per group will be included. Inclusion and exclusion criteria were set-up according to the objectives (absence of any pathology for controls, etc.) and the legislation (written consent, etc.). Thirty-two patients have already been included so far, and biopsies are stored in liquid nitrogen. Blood samples are collected just before surgery using Paxgene RNA tubes and stored following the manufacturer's instructions until analysis.

2.2. Blood sample Total RNA will be extracted from blood using Paxgene RNA Extraction kit and analysed by RNAseq 2.3. Muscle biopsies 2.3.1. Transcriptomic analysis Total RNA will be extracted from human muscle biopsies using commercial kits. The investigators will first verify that known muscles markers are up-regulated in cancer patient biopsies (positive controls) and address their levels in muscle biopsies from hemodialysis patients. We will thus perform qRT-PCR UBE2B, UBE2D2, MaFbx, MuRF1, Ozz, ASB2, E4B, Nedd4, Mdm2 and 26S proteasome subunits.

2.3.2. Proteomic analysis Proteomic analysis will be performed usin shot gun spectrometry analysis