Cyst expansion and regression in a mouse model of polycystic kidney disease.

Autosomal-dominant polycystic kidney disease is characterized by progressive cyst formation and fibrosis in the kidneys. Here we describe an orthologous Pkd1(nl,nl) mouse model, with reduced expression of the normal Pkd1 transcript, on a fixed genetic background of equal parts C57Bl/6 and 129Ola/Hsd mice (B6Ola-Pkd1(nl,nl)). In these mice, the first cysts develop from mature proximal tubules around birth. Subsequently, larger cysts become visible at day 7, followed by distal tubule and collecting duct cyst formation, and progressive cystic enlargement to develop into large cystic kidneys within 4 weeks. Interestingly, cyst expansion was followed by renal volume regression due to cyst collapse. This was accompanied by focal formation of fibrotic areas, an increased expression of genes involved in matrix remodeling and subsequently an increase in infiltrating immune cells. After an initial increase in blood urea within the first 4 weeks, renal function remained stable over time and the mice were able to survive up to a year. Also, in kidneys of ADPKD patients collapsed cysts were observed, in addition to massive fibrosis and immune infiltrates. Thus, B6Ola-Pkd1(nl,nl) mice show regression of cysts and renal volume that is not accompanied by a reduction in blood urea levels.

Accelerated antibody-mediated graft loss of rodent pancreatic islets after pretreatment with dexamethasone-treated immature donor dendritic cells.

BACKGROUND: Allogeneic islets of Langerhans transplantation is hampered in its success as a curative treatment of type 1 diabetes by the absence of potent, specific, and nontoxic immunosuppressive drugs. Here, we assessed whether donor bone marrow-derived dexamethasone-treated dendritic cells (dexDCs) could prolong islet allograft survival in a full major histocompatibility complex mismatch rat model. METHODS: Rodent allogeneic islet transplantation was performed from DA rats to Lewis rats and vice versa. Permanently immature dendritic cells were generated from the bone marrow of DA and Lewis rats by treatment with dexamethasone. Animals were either vehicle or donor dexDCs pretreated. Serum was used to monitor glucose, C-peptide, and alloreactive antibodies. RESULTS: The transplantation of DA islets into Lewis recipients showed direct graft failure with reduced numbers of ß-cells when rats were pretreated with donor dexDCs. In the reverse model (Lewis islets into DA recipients), dexDC-treated DA recipients even showed a significantly accelerated rejection of Lewis islets. Immunohistochemical analysis of allograft tissue of dexDC-treated recipients showed a predominant natural killer cell infiltration and a presence of antibody reactivity in the absence of complement deposition. Alloreactive antibodies were solely found in dexDC-treated recipients. CONCLUSION: Our study shows that pretreatment with donor-derived dexDCs induces an antibody-mediated rejection in this islet transplantation rodent model.

Dose-dependent effects of sirolimus on mTOR signaling and polycystic kidney disease.

Inhibition of the mammalian target of rapamycin (mTOR) shows beneficial effects in animal models of polycystic kidney disease (PKD); however, two clinical trials in patients with autosomal dominant PKD failed to demonstrate a short-term benefit in either the early or progressive stages of disease. The stage of disease during treatment and the dose of mTOR inhibitors may account for these differing results. Here, we studied the effects of a conventional low dose and a higher dose of sirolimus (blood levels of 3 ng/ml and 30-60 ng/ml, respectively) on mTOR activity and renal cystic disease in two Pkd1-mutant mouse models at different stages of the disease. When initiated at early but not late stages of disease, high-dose treatment strongly reduced mTOR signaling in renal tissues, inhibited cystogenesis, accelerated cyst regression, and abrogated fibrosis and the infiltration of immune cells. In contrast, low-dose treatment did not significantly reduce renal cystic disease. Levels of p-S6Rp(Ser240/244), which marks mTOR activity, varied between kidneys; severity of the renal cystic phenotype correlated with the level of mTOR activity. Taken together, these data suggest that long-term treatment with conventional doses of sirolimus is insufficient to inhibit mTOR activity in renal cystic tissue. Mechanisms to increase bioavailability or to target mTOR inhibitors more specifically to kidneys, alone or in combination with other compounds, may improve the potential for these therapies in PKD.

Altered Hippo signalling in polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by progressive deterioration of renal function and formation of cysts, and is an important cause of end-stage renal disease. Previously we showed that tubular epithelial injury accelerates cyst formation in inducible Pkd1-deletion mice. In these mice, expression of the planar cell polarity (PCP) component Four-jointed (Fjx1) is decreased during epithelial repair, while in control mice Fjx1 expression is increased and may be required during tissue regeneration. In cystic kidneys, however, Fjx1 expression is also increased. Besides a PCP component, Four-jointed is also implicated in the Hippo-signalling pathway. This pathway is involved in organ size control by regulating proliferation and apoptosis. The role of Hippo signalling, together with the opposing expression pattern of Fjx1 during epithelial repair and at cystic stages, triggered us to investigate the activity of the Hippo pathway during these processes. Therefore, we examined its final effector molecule, the transcriptional co-activator Yes-associated protein (YAP) and observed that during tissue repair, YAP expression was not different between Pkd1-deletion mice and controls, ie during tissue regeneration YAP expression was increased and predominantly localized in the cytoplasm but normalized after tissue repair. At a later stage, however, in cystic epithelia and epithelia of dilated tubules, strong nuclear YAP accumulation was observed, accompanied by up-regulation of the YAP transcriptional targets Birc-3, Ctgf, InhbA, and Fjx1. Altered activity of the Hippo pathway was confirmed in renal tissues from human ADPKD and ARPKD patients, as well as in cystic renal tumours. Our data strengthen the concept that during epithelial repair Four-jointed is involved in PCP signalling, while in cystic kidneys it is related to Hippo signalling and cyst growth.

Chimerism occurs twice as often in lupus nephritis as in normal kidneys.

OBJECTIVE: Systemic lupus erythematosus (SLE) is an immune-mediated disease that particularly affects the kidneys, causing lupus nephritis. In experimental mouse models, lupus nephritis can be mimicked by inducing a chimeric state through the injection of parental T cells in offspring. In humans, pregnancy-induced chimerism may play a role in the pathogenesis of autoimmune diseases such as SLE, but it is likely that only certain chimeric cells have pathogenic potential. In this study, we investigated whether the distribution of chimeric cells is different in the kidneys of women with SLE from that in normal kidneys, and we examined the phenotype of chimeric cells in women with SLE. METHODS: The presence of chimeric cells was investigated by in situ hybridization targeting the Y chromosome in 57 renal biopsy samples from 49 women with lupus nephritis. Fifty-one kidney autopsy specimens without histomorphologic lesions served as controls. Double-staining for the Y chromosome in combination with CD3 and CD34 markers was performed in 5 kidney specimens with lupus nephritis to identify the phenotype of the chimeric cells. RESULTS: Y chromosome-positive cells were found in 27 of 49 patients with lupus nephritis and in 13 of 51 normal controls (P < 0.01). Both CD3+ and CD34+ chimeric cells were identified in lupus nephritis kidney specimens. CONCLUSION: Chimeric cells are present significantly more often in kidneys with lupus nephritis than in normal kidneys, and some of these chimeric cells are T cells. This finding is interesting in light of experimental models demonstrating that lupus nephritis is initiated by chimeric T cells.