Serotonin (5-HT) controls a wide range of biological functions. In the brain, its implication as a neurotransmitter and in the control of behavioral traits has been largely documented. At the periphery, its modulatory role in physiological processes, such as the cardiovascular function, is still poorly understood. The rate-limiting enzyme of 5-HT synthesis, tryptophan hydroxylase (TPH), is encoded by two genes, the well characterized tph1 gene and a recently identified tph2 gene. In this article, based on the study of a mutant mouse in which the tph1 gene has been inactivated by replacement with the ␤-galactosidase gene, we establish that the neuronal tph2 is expressed in neurons of the raphe nuclei and of the myenteric plexus, whereas the nonneuronal tph1, as detected by ␤-galactosidase expression, is in the pineal gland and the enterochromaffin cells. Anatomic examination of the mutant mice revealed larger heart sizes than in wild-type mice. Histological investigation indicates that the primary structure of the heart muscle is not affected. Hemodynamic analyses demonstrate abnormal cardiac activity, which ultimately leads to heart failure of the mutant animals. This report links loss of tph1 gene expression, and thus of peripheral 5-HT, to a cardiac dysfunction phenotype. The tph1 ؊/؊ mutant may be valuable for investigating cardiovascular dysfunction observed in heart failure in humans. S erotonin (5-hydroxytryptamine, 5-HT) was discovered in blood as a vasoconstrictor of large vessels (1). Subsequently, it has been found in the gastrointestinal tract as a contractile substance identical with enteramine (2), in the CNS as a neurotransmitter (3), and in the pineal gland as an intermediate in the synthesis of melatonin, the neurohormone implicated in the circadian rhythmicity of physiological functions (4). 5-HT is detected early during brain development, suggesting its involvement in neuronal proliferation, migration, and differentiation (5). 5-HT modulates a variety of behavioral functions, including regulation of sleep͞wakefulness, appetite, nociception, mood, stress, and maternal or sexual behavior (6). Altered regulation of 5-HT in human affects behavioral traits and personality disorders, such as impulsive aggression, manic depressive illness, anxiety and alcoholism, and neurological conditions, such as migraine (7-10).About 95% of the 5-HT in the periphery is in the gastrointestinal tract (11), where it initiates responses as diverse as nausea, intestinal secretion, and peristaltis and has been implicated in gastroenteric diseases, such as irritable bowel syndrome (12). The 5-HT originating from the gastrointestinal tract is stored in blood platelets and participates in blood coagulation and pressure and in homeostasis. In the heart, an increased 5-HT availability has been shown to produce arrhythmia, leading to heart block or to valvular fibroplasia (13). 5-HT has also been suggested to regulate cardiovascular development (14). Recently, disruption of 5HT-2B receptor revealed a role for 5-HT by means of...

Rapidly progressive glomerulonephritis (RPGN) is a clinical a morphological expression of severe glomerular injury. Glomerular injury manifests as a proliferative histological pattern (“crescents”) with accumulation of T cells and macrophages, and proliferation of intrinsic glomerular cells. We show de novo induction of heparin-binding epidermal growth factor-like growth factor (HB-EGF) in intrinsic glomerular epithelial cells (podocytes) from both mice and humans with RPGN. HB-EGF induction increases phosphorylation of the EGFR/ErbB1 receptor in mice with RPGN. In HB-EGF-deficient mice, EGFR activation in glomeruli is absent and the course of RPGN is improved. Autocrine HB-EGF induces a phenotypic switch in podocytes in vitro. Conditional deletion of the Egfr gene from podocytes of mice alleviates the severity of RPGN. Pharmacological blockade of EGFR also improves the course of RPGN, even when started 4 days after the induction of experimental RPGN. This suggests that targeting the HB-EGF/EGFR pathway could also be beneficial for treatment of human RPGN.

The early appearance of serotonin and its receptors during prenatal development, together with the many effects serotonin exerts during CNS morphogenesis, strongly suggest that serotonin influences the development and maturation of the mammalian brain before it becomes a neuromodulator/neurotransmitter. Sites of early serotonin biosynthesis, however, have not been detected in mouse embryos or extraembryonic structures, suggesting that the main source of serotonin could be of maternal origin. This hypothesis was tested by using knockout mice lacking the tph1 gene, which is responsible for the synthesis of peripheral serotonin. Genetic crosses were performed to compare the phenotype of pups born from homozygous and heterozygous mothers. Observations provide the first clear evidence that (i) maternal serotonin is involved in the control of morphogenesis during developmental stages that precede the appearance of serotonergic neurons and (ii) serotonin is critical for normal murine development. Most strikingly, the phenotype of tph1؊/؊ embryos depends more on the maternal genotype than on that of the concepti. Consideration of the maternal genotype may thus help to clarify the influence of other genes in complex diseases, such as mental illness.genotype/phenotype ͉ tph1 knockout mice ͉ tryptophan hydroxylase S erotonin participates in a wide range of physiological systems including the control of gastrointestinal motility and secretion, cardiovascular regulation, hemostatic processes, the regulation of circadian rhythms, the sleep-wake cycle, perception of pain, appetite, manifestation of nausea, and sexual behavior. Accumulating in vitro evidence also indicates that serotonin signaling participates in the regulation of development in many animal phyla before the onset of neurogenesis. Serotonin thus plays a role in development before it acts as a neurotransmitter (1-3). Serotonin affects craniofacial, gastrointestinal, and cardiovascular morphogenesis in chicken, rat, and mouse; these effects are often mediated by the serotonin 2B receptor (4-7). Altogether, the presence of serotonin, its receptors, and transporter during development and the ability of compounds that modulate serotonergic signaling to interfere with development suggest that serotonin functions as a humoral morphogen (8-10). Sites of early serotonin biosynthesis, however, have not been detected in embryos or extraembryonic structures of the mouse. It has therefore been assumed that the main source of serotonin is maternal (11).We have generated a mouse line deficient in peripheral serotonin biosynthesis. Targeted disruption of the tryptophan hydroxylase 1 (tph1) gene resulted in levels of circulating serotonin that are only 3-15% of those of normal mice. The null mutants (tph1Ϫ/Ϫ) from heterozygous crosses are viable and display no gross anatomical abnormalities, but they develop cardiac insufficiency in adulthood (12). The tph1Ϫ/Ϫ mice thus provide a convenient tool to address the developmental role of maternal serotonin. tph1-null females were bred...

No abstract

Interstitial fibrosis is a powerful pejorative predictor of progression of nephropathies in a variety of chronic renal diseases. It is characterized by the depletion of kidney cells and their replacement by extracellular matrix, in particular, type-I fibrillar collagen, a protein scarce in normal interstitium. However, assessment of fibrosis remains a challenge in research and clinical pathology. We develop a novel methodology based on second harmonic generation (SHG) microscopy, and we image collagen fibers in human and mouse unstained kidneys. We take into account the variability in renal shape, and we develop automated image processing for quantitative scoring of thick murine tissues. This approach allows quantitative 3-D imaging of interstitial fibrosis and arterial remodeling with high accuracy. Moreover, SHG microscopy helps to raise pathophysiological questions. First, imaging of a large volume within a mouse kidney shows that progression of fibrosis is a heterogeneous process throughout the different renal compartments. Second, SHG from fibrillar collagens does not overlap with the glomerular tuft, despite patent clinical and experimental glomerulosclerosis. Since glomerulosclerosis involves SHG-silent nonfibrillar collagens, our work supports pathophysiological differences between interstitial fibrosis and glomerulosclerosis, a clearly nonfibrotic process.

The mechanisms driving the development of extracapillary lesions in focal segmental glomerulosclerosis (FSGS) and crescentic glomerulonephritis (CGN) remain poorly understood. A key question is how parietal epithelial cells (PECs) invade glomerular capillaries, thereby promoting injury and kidney failure. Here we show that expression of the tetraspanin CD9 increases markedly in PECs in mouse models of CGN and FSGS, and in kidneys from individuals diagnosed with these diseases. Cd9 gene targeting in PECs prevents glomerular damage in CGN and FSGS mouse models. Mechanistically, CD9 deficiency prevents the oriented migration of PECs into the glomerular tuft and their acquisition of CD44 and β1 integrin expression. These findings highlight a critical role for de novo expression of CD9 as a common pathogenic switch driving the PEC phenotype in CGN and FSGS, while offering a potential therapeutic avenue to treat these conditions.

Connective tissue growth factor (CTGF), a matrix-associated protein with four distinct cytokine binding domains, has roles in vasculogenesis, wound healing responses, and fibrogenesis and is upregulated in fibroblasts and myofibroblasts in disease. Here, we investigated the role of CTGF in fibrogenic cells. In mice, tissue-specific inducible overexpression of CTGF by kidney pericytes and fibroblasts had no bearing on nephrogenesis or kidney homeostasis but exacerbated inflammation and fibrosis after ureteral obstruction. These effects required the WNT receptor LDL receptor-related protein 6 (LRP6). Additionally, pericytes isolated from these mice became hypermigratory and hyperproliferative on overexpression of CTGF. CTGF is cleaved into distinct domains. Treatment with recombinant domain 1, 1+2 (N terminus), or 4 (C terminus) independently activated myofibroblast differentiation and wound healing responses in cultured pericytes, but domain 4 showed the broadest profibrotic activity. Domain 4 exhibited low-affinity binding to LRP6 in binding assays, and inhibition of LRP6 or critical signaling cascades downstream of LRP6, including JNK and WNT/-catenin, inhibited the biologic activity of domain 4. Administration of blocking antibodies specifically against CTGF domain 4 or recombinant Dickkopf-related protein-1, an endogenous inhibitor of LRP6, effectively inhibited inflammation and fibrosis associated with ureteral obstruction Therefore, domain 4 of CTGF and the WNT signaling pathway are important new targets in fibrosis.

The identification of patients at increased risk for chronic kidney disease offers the potential to prevent or delay end-stage renal disease and the associated cardiovascular events. Data from recently completed controlled clinical trials of endothelin (ET) receptor blockers confirmed their potent antiproteinuric effect after a number of preclinical studies. A spectrum of proteinuric glomerular diseases results from podocyte abnormalities and, in return, impact podocyte structure and function. Because podocytes are cells in the glomerulus that form a crucial component of the glomerular filtration barrier, contributing to size selectivity and maintaining a large filtration surface, we focus on evidence that suggest ET-1 may promote podocyte injury thereby aggravating albumin urinary loss and alteration of the glomerular microvasculature. Systematic confrontation of animal models and studies in human subjects should help decipher pathophysiological mechanisms whereby the local renal ET system promotes podocyte injury and chronic kidney disease in specific pathophysiological contexts. Current evidence suggests that more experimental and clinical attention should be paid to conditions with increased vascular or endocapillary ET-1 production on the one hand, and in diseases with altered podocyte phenotype and survival such as focal segmental glomerulosclerosis and crescentic glomerulonephritis on the other. These conclusions may assist clinicians in creating optimal clinical trials for patients at increased risk for or with overt chronic kidney disease.