Altered renal morphology in transgenic mice with cholecystokinin overexpression

Knockout of aminopeptidase A in mice causes functional alterations and morphological glomerular basement membrane changes in the kidneys

Aminopeptidase A is one of the most potent enzymes within the renin-angiotensin system in terms of angiotensin II degradation. Here, we examined whether there is a kidney phenotype and any compensatory changes in other renin angiotensin system enzymes involved in the metabolism of angiotensin II associated with aminopeptidase A deficiency. Kidneys harvested from aminopeptidase A knockout mice were examined by light and electron microscopy, immunohistochemistry and immunofluorescence. Kidney angiotensin II levels and the ability of renin angiotensin system enzymes in the glomerulus to degrade angiotensin II ex vivo, their activities, protein and mRNA levels in kidney lysates were evaluated. Knockout mice had increased blood pressure and mild glomerular mesangial expansion without significant albuminuria. By electron microscopy, knockout mice exhibited a mild increase of the mesangial matrix, moderate thickening of the glomerular basement membrane but a striking appearance of knob-like structures. These knobs were seen in both male and female mice and persisted after the treatment of hypertension. In isolated glomeruli from knockout mice, the level of angiotensin II was more than three-fold higher as compared to wild type control mice. In kidney lysates from knockout mice angiotensin converting enzyme activity, protein and mRNA levels were markedly decreased possibly as a compensatory mechanism to reduce angiotensin II formation. Thus, our findings support a role for aminopeptidase A in the maintenance of glomerular structure and intra-kidney homeostasis of angiotensin peptides.

Gastrin, Cholecystokinin, Signaling, and Biological Activities in Cellular Processes

The structurally-related peptides, gastrin and cholecystokinin (CCK), were originally discovered as humoral stimulants of gastric acid secretion and pancreatic enzyme release, respectively. With the aid of methodological advances in biochemistry, immunochemistry, and molecular biology in the past several decades, our concept of gastrin and CCK as simple gastrointestinal hormones has changed considerably. Extensive in vitro and in vivo studies have shown that gastrin and CCK play important roles in several cellular processes including maintenance of gastric mucosa and pancreatic islet integrity, neurogenesis, and neoplastic transformation. Indeed, gastrin and CCK, as well as their receptors, are expressed in a variety of tumor cell lines, animal models, and human samples, and might contribute to certain carcinogenesis. In this review, we will briefly introduce the gastrin and CCK system and highlight the effects of gastrin and CCK in the regulation of cell proliferation and apoptosis in both normal and abnormal conditions. The potential imaging and therapeutic use of these peptides and their derivatives are also summarized.

Cholecystokinin-From Local Gut Hormone to Ubiquitous Messenger

Cholecystokinin (CCK) was discovered in 1928 in jejunal extracts as a gallbladder contraction factor. It was later shown to be member of a peptide family, which are all ligands for the CCK₁ and CCK₂ receptors. CCK peptides are known to be synthetized in small intestinal endocrine I-cells and cerebral neurons. But in addition, CCK is expressed in several endocrine glands (pituitary cells, thyroid C-cells, pancreatic islets, the adrenals, and the testes); in peripheral nerves; in cortical and medullary kidney cells; in cardial myocytes; and in cells of the immune system. CCK peptides stimulate pancreatic enzyme secretion and growth, gallbladder contraction, and gut motility, satiety and inhibit acid secretion from the stomach. Moreover, they are major neurotransmitters in the brain and the periphery. CCK peptides also stimulate calcitonin, insulin, and glucagon secretion, and they may act as natriuretic peptides in the kidneys. CCK peptides are derived from proCCK with a C-terminal bioactive YMGWMDFamide sequence, in which the Y-residue is partly O-sulfated. The plasma forms are CCK-58, -33, -22, and -8, whereas the small CCK-8 and -5 are potent neurotransmitters. Over the last decades, CCK expression has also been encountered in tumors (neuroendocrine tumors, cerebral astrocytomas, gliomas, acoustic neuromas, and specific pediatric tumors). Recently, a metastastic islet cell tumor was found to cause a specific CCKoma syndrome, suggesting that circulating CCK may be a useful tumor marker.

Low protein diet inhibits uric acid synthesis and attenuates renal damage in streptozotocin-induced diabetic rats

AIM

Several studies indicated that hyperuricemia may link to the worsening of diabetic nephropathy (DN). Meanwhile, low protein diet (LPD) retards exacerbation of renal damage in chronic kidney disease. We then assessed whether LPD influences uric acid metabolism and benefits the progression of DN in streptozotocin- (STZ-) induced diabetic rats.

METHODS

STZ-induced and control rats were both fed with LPD (5%) and normal protein diet (18%), respectively, for 12 weeks. Vital signs, blood and urinary samples for UA metabolism were taken and analyzed every 3 weeks. Kidneys were removed at the end of the experiment.

RESULTS

Diabetic rats developed into constantly high levels of serum UA (SUA), creatinine (SCr) and 24 h amounts of urinary albumin excretion (UAE), creatinine (UCr), urea nitrogen (UUN), and uric acid (UUA). LPD significantly decreased SUA, UAE, and blood glucose, yet left SCr, UCr, and UUN unchanged. A stepwise regression showed that high UUA is an independent risk factor for DN. LPD remarkably ameliorated degrees of enlarged glomeruli, proliferated mesangial cells, and hyaline-degenerated tubular epithelial cells in diabetic rats. Expression of TNF-α in tubulointerstitium significantly decreased in LPD-fed diabetic rats.

CONCLUSION

LPD inhibits endogenous uric acid synthesis and might accordingly attenuate renal damage in STZ-induced diabetic rats.

Cholecystokinin plays a novel protective role in diabetic kidney through anti-inflammatory actions on macrophage: anti-inflammatory effect of cholecystokinin

Inflammatory process is involved in the pathogenesis of diabetic nephropathy. In this article, we show that cholecystokinin (CCK) is expressed in the kidney and exerts renoprotective effects through its anti-inflammatory actions. DNA microarray showed that CCK was upregulated in the kidney of diabetic wild-type (WT) mice but not in diabetic intracellular adhesion molecule-1 knockout mice. We induced diabetes in CCK-1 receptor (CCK-1R) and CCK-2R double-knockout (CCK-1R(-/-),-2R(-/-)) mice, and furthermore, we performed a bone marrow transplantation study using CCK-1R(-/-) mice to determine the role of CCK-1R on macrophages in the diabetic kidney. Diabetic CCK-1R(-/-),-2R(-/-) mice revealed enhanced albuminuria and inflammation in the kidney compared with diabetic WT mice. In addition, diabetic WT mice with CCK-1R(-/-) bone marrow-derived cells developed more albuminuria than diabetic CCK-1R(-/-) mice with WT bone marrow-derived cells. Administration of sulfated cholecystokinin octapeptide (CCK-8S) ameliorated albuminuria, podocyte loss, expression of proinflammatory genes, and infiltration of macrophages in the kidneys of diabetic rats. Furthermore, CCK-8S inhibited both expression of tumor necrosis factor-α and chemotaxis in cultured THP-1 cells. These results suggest that CCK suppresses the activation of macrophage and expression of proinflammatory genes in diabetic kidney. Our findings may provide a novel strategy of therapy for the early stage of diabetic nephropathy.

Effects of angiotensin receptor blocker on phenotypic alterations of podocytes in early diabetic nephropathy

BACKGROUND

Emerging evidence suggests that podocyte injury is a crucial event in the stage of diabetic nephropathy (DN), a process in which angiotensin II is implicated. In this study, the authors investigated the influence of irbesartan, an angiotensin receptor blocker, on the phenotypic alterations of podocytes in experimental DN.

METHODS

DN was induced by combination of high-sucrose, high-fat diet and intraperitoneal injection of low dose of streptozotocin (35 mg/kg) in spontaneously hypertensive rats. Diabetic rats were treated with irbesartan (50 mg/kg/d) by gavage for 8 weeks. Nondiabetic normotensive Wistar-Kyoto rats, which have the same genetic background as spontaneously hypertensive rat, were used as controls. The renal histological changes were investigated by light and electron microscopy. The epithelial marker of nephrin and mesenchymal marker of desmin were detected by real-time reverse transcriptase-polymerase chain reaction and Western blotting.

RESULTS

Compared with controls, diabetic rats were associated with mesangial matrix deposition, thickening of glomerular basement membrane, albuminuria, loss of podocytes and effacement of foot processes. Furthermore, the expression of nephrin was significantly reduced whereas desmin was increased. Irbesartan treatment not only lowered blood pressure and albuminuria but also attenuated podocyte loss, maintenance of nephrin expression and inhibition of desmin expression.

CONCLUSIONS

This study demonstrates that early irbesartan intervention attenuates the podocyte damage and ameliorates phenotypic alterations of podocytes, which provides a novel insight for the early application of angiotensin receptor blocker to prevent the development of DN.