In Vitro Effects of Thymoglobulin in Human Embryonic Kidney Cell Line (HEK293) in Culture.

BACKGROUND: Anti-thymocyte globulins are polyclonal T-cell-depleting immunoglobulins used in induction of immunosuppression in kidney transplant recipients. Thymoglobulin is purified rabbit immunoglobulin (Ig)G, obtained by immunization of rabbits with fetal human thymus, which depletes T lymphocytes by complement-dependent lysis and apoptosis, reduces production of cytokines, and decreases expression of adhesion molecules in endothelial cells. METHODS: To determine possible direct effects of Thymoglobulin on kidney cells during transplantation, we used the Human Embryonic Kidney cell line (HEK293) in culture. We measured membrane potential of the cells by use of the slow whole patch-clamp technique. We determined effects of Thymoglobulin on cell death and proliferation during hypoxia/re-oxygenation injury, using a hypoxic chamber. RESULTS: Depolarizations of HEK293 cells caused by Thymoglobulin were concentration-dependent and membrane potential-dependent, showing direct effects of Thymoglobulin on the HEK293 cells, whereas rabbit anti-thymocyte globulin produced against Jurkat cells (ATG-F) and normal rabbit IgG had no effects. To determine the effects of Thymoglobulin in hypoxia/re-oxygenation conditions, cells were incubated for 24 hours with Thymoglobulin in an atmosphere with 5% CO2-95% N2 at 37°C followed by 1 hour in atmosphere with 5% CO2-95% air at 37°C. The effects of hypoxia/re-oxygenation were detected by calculating cell death and determining the cell growth, using scratch test. CONCLUSIONS: Thymoglobulin prevented the cell death induced by hypoxia and re-oxygenation conditions. In addition, it accelerated the cell growth (improved scratch wound-healing). This is the first study to show the direct effects of Thymoglobulin on kidney-derived epithelial cells, which may lead to better understanding of its effects in kidney transplantation.

High salt intake increases uroguanylin expression in mouse kidney.

The intestinal peptides, guanylin and uroguanylin, may have an important role in the endocrine control of renal function. Both peptides and their receptor, guanylyl cyclase C (GC-C), are also expressed within the kidney, suggesting that they may act locally in an autocrine/paracrine fashion. However, their physiological regulation within the kidney has not been studied. To begin to address this issue, we evaluated the distribution of uroguanylin and guanylin messenger RNA (mRNA) in the mouse nephron and the regulation of renal expression by changes in dietary salt/water intake. Expression was determined in 1) wild-type mice, 2) two strains of receptor-guanylyl cyclase-deficient mice (ANP-receptor-deficient, GC-A-/-, and GC-C-deficient mice); and 3) cultured renal epithelial (M-1) cells, by RT-PCR, Northern blotting and immunocytochemistry. Renal uroguanylin messenger RNA expression was higher than guanylin and had a different distribution pattern, with highest levels in the proximal tubules, whereas guanylin was mainly expressed in the collecting ducts. Uroguanylin expression was significantly lower in GC-C-/- mice than in GC-A-/- and wild-types, suggesting that absence of a receptor was able to down-regulate ligand expression. Salt-loading (1% NaCl in drinking water) increased uroguanylin-mRNA expression by >1.8-fold but had no effect on guanylin expression. Uroguanylin but not guanylin transcripts were detected in M-1 cells and increased in response to hypertonic media (+NaCl or mannitol). Our results indicate that high-salt intake increases uroguanylin but not guanylin expression in the mouse kidney. The synthesis of these peptides by tubular epithelium may contribute to the local control of renal function and its adaptation to dietary salt.

Presence and activation of nuclear phosphoinositide 3-kinase C2beta during compensatory liver growth.

Highly purified liver nuclei incorporated radiolabeled phosphate into phosphatidylinositol 4-phosphate (PtdIns(4)P), PtdIns(4,5)P(2), and PtdIns(3,4,5)P(3). When nuclei were depleted of their membrane, no radiolabeling of PtdIns(3,4,5)P(3) could be detected showing that within the intranuclear region there are no class I phosphoinositide 3-kinases (PI3K)s. In membrane-depleted nuclei harvested 20 h after partial hepatectomy, the incorporation of radiolabel into PtdIns(3)P was observed together with an increase in immunoprecipitable PI3K-C2beta activity, which is sensitive to wortmannin (10 nm) and shows strong preference for PtdIns over PtdIns(4)P as a substrate. On Western blots PI3K-C2beta revealed a single immunoreactive band of 180 kDa, whereas 20 h after partial hepatectomy gel shift of 18 kDa was noticed, suggesting that observed activation of enzyme is achieved by proteolysis. When intact membrane-depleted nuclei were subjected to short term (20 min) exposure to micro-calpain, similar gel shift together with an increase in PI3K-C2beta activity was observed, when compared with the nuclei harvested 20 h after partial hepatectomy. Moreover, the above-mentioned gel shift and increase in PI3K-C2beta activity could be prevented by the calpain inhibitor calpeptin. The data presented in this report show that, in the membrane-depleted nuclei during the compensatory liver growth, there is an increase in PtdIns(3)P formation as a result of PI3K-C2beta activation, which may be a calpain-mediated event.