Periostin: a matricellular protein involved in peritoneal injury during peritoneal dialysis.

BACKGROUND: Periostin is a matricellular protein involved in tissue remodeling through the promotion of adhesion, cell survival, cellular dedifferentiation, and fibrogenesis. It can be induced by transforming growth factor beta and high glucose concentrations. We hypothesized that this protein might be expressed in the peritoneal cavity of patients on peritoneal dialysis (PD) and even more in patients with signs of encapsulating peritoneal sclerosis (EPS). METHOD: In this retrospective study, we included peritoneal biopsies from patients on PD with EPS (n = 7) and without signs of EPS (n = 10), and we compared them with biopsies taken during hernia repair from patients not on PD (n = 11) and during various procedures from uremic patients not on PD (n = 6). Periostin was localized by immunohistochemistry, scored semiquantitatively, and quantified by morphometry. Periostin protein concentrations were measured by ELISA in dialysates from 15 patients. Periostin messenger RNA was quantified in vitro in peritoneal fibroblasts. RESULTS: In control biopsies, periostin was present in the walls of larger arteries and focally in extracellular matrix in the submesothelial zone. Patients on PD demonstrated interstitial periostin in variable amounts depending on the severity of submesothelial fibrosis. In EPS, periostin expression was very prominent in the sclerosis layer. The area of periostin was significantly larger in EPS biopsies than in control biopsies, and the percentage of periostin-positive area correlated with the thickness of the submesothelial fibrosis zone. Periostin concentrations in dialysate increased significantly with time on PD in patients without signs of EPS; in patients with EPS, periostin concentrations in dialysate were low and demonstrated the smallest increase with time. In vitro, periostin was found to be strongly expressed by peritoneal fibroblasts. CONCLUSION: Periostin is strongly expressed by fibroblasts and deposited in the peritoneal cavity of patients with EPS and with simple peritoneal fibrosis on PD. This protein might play a role in the progression of peritoneal injury, and low levels of periostin after prolonged time on PD might be a marker of EPS.

Periostin is induced in glomerular injury and expressed de novo in interstitial renal fibrosis.

Matricellular proteins participate in the pathogenesis of chronic kidney diseases. We analyzed glomerular gene expression profiles from patients with proteinuric diseases to identify matricellular proteins contributing to the progression of human nephropathies. Several genes encoding matricellular proteins, such as SPARC, THBS1, and CTGF, were induced in progressive nephropathies, but not in nonprogressive minimal-change disease. Periostin showed the highest induction, and its transcript levels correlated negatively with glomerular filtration rate in both glomerular and tubulointerstitial specimen. In well-preserved renal tissue, periostin localized to the glomerular tuft, the vascular pole, and along Bowman's capsule; no signal was detected in the tubulointerstitial compartment. Biopsies from patients with glomerulopathies and renal dysfunction showed enhanced periostin expression in the mesangium, tubular interstitium, and sites of fibrosis. Periostin staining correlated negatively with renal function. α-smooth muscle actin-positive mesangial and interstitial cells localized close to periostin-positive sites, as indicated by co-immunofluorescence. In vitro stimulation of mesangial cells by external addition of TGF-ß1 resulted in robust induction of periostin. Addition of periostin to mesangial cells induced cell proliferation and decreased the number of cells expressing activated caspase-3, a marker of apoptosis. These human data indicate for the first time a role of periostin in glomerular and interstitial injury in acquired nephropathies.

Systematic analysis of a novel human renal glomerulus-enriched gene expression dataset.

Glomerular diseases account for the majority of cases with chronic renal failure. Several genes have been identified with key relevance for glomerular function. Quite a few of these genes show a specific or preferential mRNA expression in the renal glomerulus. To identify additional candidate genes involved in glomerular function in humans we generated a human renal glomerulus-enriched gene expression dataset (REGGED) by comparing gene expression profiles from human glomeruli and tubulointerstitium obtained from six transplant living donors using Affymetrix HG-U133A arrays. This analysis resulted in 677 genes with prominent overrepresentation in the glomerulus. Genes with 'a priori' known prominent glomerular expression served for validation and were all found in the novel dataset (e.g. CDKN1, DAG1, DDN, EHD3, MYH9, NES, NPHS1, NPHS2, PDPN, PLA2R1, PLCE1, PODXL, PTPRO, SYNPO, TCF21, TJP1, WT1). The mRNA expression of several novel glomerulus-enriched genes in REGGED was validated by qRT-PCR. Gene ontology and pathway analysis identified biological processes previously not reported to be of relevance in glomeruli of healthy human adult kidneys including among others axon guidance. This finding was further validated by assessing the expression of the axon guidance molecules neuritin (NRN1) and roundabout receptor ROBO1 and -2. In diabetic nephropathy, a prevalent glomerulopathy, differential regulation of glomerular ROBO2 mRNA was found.In summary, novel transcripts with predominant expression in the human glomerulus could be identified using a comparative strategy on microdissected nephrons. A systematic analysis of this glomerulus-specific gene expression dataset allows the detection of target molecules and biological processes involved in glomerular biology and renal disease.

Human nephrosclerosis triggers a hypoxia-related glomerulopathy.

In the kidney, hypoxia contributes to tubulointerstitial fibrosis, but little is known about its implications for glomerular damage and glomerulosclerosis. Chronic hypoxia was hypothesized to be involved in nephrosclerosis (NSC) or "hypertensive nephropathy." In the present study genome-wide expression data from microdissected glomeruli were studied to examine the role of hypoxia in glomerulosclerosis of human NSC. Functional annotation analysis revealed prominent regulation of hypoxia-associated biological processes in NSC, including angiogenesis, fibrosis, and inflammation. Glomerular expression levels of a majority of genes regulated by the hypoxia-inducible factors (HIFs) were significantly altered in NSC. Among these HIF targets, chemokine C-X-C motif receptor 4 (CXCR4) was prominently induced. Glomerular CXCR4 mRNA induction was confirmed by quantitative RT-PCR in an independent cohort with NSC but not in those with other glomerulopathies. By immunohistological analysis, CXCR4 showed enhanced positivity in podocytes in NSC biopsy specimens. This CXCR4 positivity was associated with nuclear localization of HIF1alpha only in podocytes of NSC, indicating transcriptional activity of HIF. As the CXCR4 ligand CXCL12/SDF-1 is constitutively expressed in podocytes, autocrine signaling may contribute to NSC. In addition, a blocking CXCR4 antibody caused significant inhibition of wound closure by podocytes in an in vitro scratch assay. These data support a role for CXCR4/CXCL12 in human NSC and indicate that hypoxia not only is involved in tubulointerstitial fibrosis but also contributes to glomerular damage in NSC.