Transforming growth factor-β (TGF-β) is a profibrotic cytokine found in chronic renal diseases, which initiates and modulates a variety of pathophysiological processes. It is synthesized by many renal cell types and exerts its biological functions through a variety of signalling pathways, including the Smad and MAPK pathways. In renal diseases, TGF-β is upregulated and induces renal cells to produce extracellular matrix proteins leading to glomerulosclerosis as well as tubulointerstitial fibrosis. Different types of renal cells undergo different pathophysiological changes induced by TGF-β, leading to apoptosis, hypertrophy and abnormalities of podocyte foot processes, which ultimately result in renal dysfunction. In this review, we describe the effects of TGF-β on different renal cell types and the means by which TGF-β participates in the pathomechanisms of glomerular and tubulointerstitial diseases.

The pathophysiology of diabetic nephropathy (DN), one of the most serious complications in diabetic patients and the leading cause of end-stage renal disease worldwide, is complex and not fully elucidated. A typical hallmark of DN is the excessive deposition of extracellular matrix (ECM) proteins in the glomerulus and in the renal tubulointerstitium, eventually leading to glomerulosclerosis and interstitial fibrosis. Although it is obvious that myofibroblasts play a major role in the synthesis and secretion of ECM, the origin of myofibroblasts in DN remains the subject of controversial debates. A number of studies have focused on epithelial-to-mesenchymal transition (EMT) as one source of matrix-generating fibroblasts in the diseased kidney. EMT is characterized by the acquisition of mesenchymal properties by epithelial cells, preferentially proximal tubular cells and podocytes. In this review we comprehensively review the literature and discuss arguments both for and against a function of EMT in renal fibrosis in DN. While the precise extent of the contribution to nephrotic fibrosis is certainly arduous to quantify, the picture that emerges from this extensive body of literature suggests EMT as a major source of myofibroblasts in DN.

The aryl hydrocarbon receptor (AhR) regulates the toxicity of environmental contaminants such as 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD). As the physiological role of the AhR in the ovary is unknown, the purpose of this study was to test the hypothesis that the AhR regulates the appearance and numbers of ovarian follicles. Ovaries were harvested from AhR-deficient (AhRKO) and wild-type mice on gestational day 18 (GD 18) and postnatal days (PND) 2-3, 8, 32-35, and 53. Complete serial sections of ovaries were evaluated histologically for the presence of germ cells and follicles. On GD 18, there was no difference in the number of germ cells per ovary between AhRKO and wild-type fetuses. However, by PND 2-3, AhRKO mice had significantly more fully formed primordial follicles (AhRKO = 38,440 +/- 3632 versus wild-type = 21,120 +/- 2688) and fewer single germ cells than wild-type mice (AhRKO = 12,696 +/- 1192 vs. wild-type = 18,160 +/- 720). On PND 8 and 32-35, there was no difference in the number of follicles between AhRKO and wild-type mice but by PND 53, AhRKO mice had significantly fewer antral follicles than wild-type (AhRKO = 3416 +/- 480 vs. wild-type = 6776 +/- 1024). Taken together, these results suggest that the AhR may play a role in the formation of primordial follicles and the regulation of antral follicle numbers.

Background Reports of malformed frogs have increased throughout the North American continent in recent years. Most of the observed malformations have involved the hind limbs. The goal of this study was to accurately characterize the hind limb malformations in wild frogs as an important step toward understanding the possible etiologies. Methods During 1997 and 1998, 182 recently metamorphosed northern leopard frogs (Rana pipiens) were collected from Minnesota, Vermont, and Maine. Malformed hind limbs were present in 157 (86%) of these frogs, which underwent necropsy and radiographic evaluation at the National Wildlife Health Center. These malformations are described in detail and classified into four major categories: (1) no limb (amelia); (2) multiple limbs or limb elements (polymelia, polydactyly, polyphalangy); (3) reduced limb segments or elements (phocomelia, ectromelia, ectrodactyly, and brachydactyly; and (4) distally complete but malformed limb (bone rotations, bridging, skin webbing, and micromelia). Results Amelia and reduced segments and/or elements were the most common finding. Frogs with bilateral hind limb malformations were not common, and in only eight of these 22 frogs were the malformations symmetrical. Malformations of a given type tended to occur in frogs collected from the same site, but the types of malformations varied widely among all three states, and between study sites within Minnesota. Conclusions Clustering of malformation type suggests that developmental events may produce a variety of phenotypes depending on the timing, sequence, and severity of the environmental insult. Hind limb malformations in free‐living frogs transcend current mechanistic explanations of tetrapod limb development. Teratology 62:151–171, 2000. Published 2000 Wiley‐Liss, Inc.

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