Issue published February 15, 2002

S tress-induced downregulation of spermatogenesis remains poorly understood. This study examined the induction of heme oxygenase-1 (HO-1), a carbon monoxide–generating inducible enzyme, in modulation of spermatogenesis. Rats were exposed to cadmium chloride (CdCl₂), a stressor causing oligozoospermia, and HO-1–induction was monitored by following HO isozyme expression. CdCl₂-treated testes increased HO-1 activity and suppressed microsomal cytochromes P450, which are required for steroidogenesis. CdCl₂-elicited HO-1 occurred mostly in Leydig cells and coincided with CO generation, as judged by bilirubin-IXα immunoreactivity. Under these circumstances, germ cells in peripheral regions of seminiferous tubules exhibited apoptosis; laser flow cytometry revealed that these apoptotic cells involve diploid and tetraploid germ cells, suggesting involvement of spermatogonia and primary spermatocytes in CdCl₂-elicited apoptosis. Pretreatment with zinc protoporphyrin-IX, an HO inhibitor, but not copper protoporphyrin-IX, which does not block the enzyme, attenuated the CdCl₂-induced apoptosis. Such antiapoptotic effects of zinc protoporphyrin-IX were repressed by supplementation of dichloromethane, a CO donor. Upon CdCl₂-treatment, both Sertoli cells and the germ cells upregulated Fas ligand; this event was also suppressed by zinc protoporphyrin-IX and restored by dichloromethane. Thus, Leydig cells appear to use HO-1–derived CO to trigger apoptosis of premeiotic germ cells and thereby modulate spermatogenesis under conditions of stress.

T hree genes, TTF1, TTF2, and PAX8, involved in thyroid gland development and migration have been identified. Yet systematic screening for defects in these genes in thyroid dysgenesis gave essentially negative results. In particular, no TTF1 gene defects were found in 76 individuals with thyroid dysgenesis even though a deletion of this gene in the mouse results in thyroid and lung agenesis and defective diencephalon. We report a 6-year-old boy with predominant dyskinesia, neonatal respiratory distress, and mild hyperthyrotropinemia. One allele of his TTF1 gene had a guanidine inserted into codon 86 producing a nonsense protein of 407, rather than 371, amino acids. The mutant TTF1 did not bind to its canonical cis-element or transactivate a reporter gene driven by the thyroglobulin promoter, a natural target of TTF1. Failure of the mutant TTF1 to interfere with binding and transactivation functions of the wild-type TTF1 suggested that the syndrome was caused by haploinsufficiency. This was confirmed in mice heterozygous for Ttf1 gene deletion, heretofore considered to be normal. Compared with wild-type littermates, Ttf1^+/– mice had poor coordination and a significant elevation of serum thyrotropin. Therefore, haploinsufficiency of the TTF1 gene results in a predominantly neurological phenotype and secondary hyperthyrotropinemia.

T he occurrence of neurological symptoms and developmental delay in patients affected by congenital hypothyroidism (CH) has been attributed to the lack of thyroid hormone in the developing CNS. Accordingly, after the introduction of neonatal screening programs for CH, which allowed early and adequate treatment, an almost normal outcome for most CH patients could be achieved. However, a few patients did not reach this favorable outcome despite early and adequate treatment. Here we describe five patients with variable degrees of CH who suffered from choreoathetosis, muscular hypotonia, and pulmonary problems, an association of symptoms that had not been described before this study. Since this clinical picture matched the phenotype of mice targeted for deletion of the transcription factor gene Nkx2-1, we investigated the human NKX2-1 gene in these five patients. We found heterozygous loss of function mutations in each of these five patients, e.g., one complete gene deletion, one missense mutation (G2626T), and three nonsense mutations (2595insGG, C2519A, C1302A). Therefore, the unfavorable outcome in patients with CH, especially those with choreoathetosis and pulmonary symptoms, can be explained by mutations in the NKX2-1 gene rather than by hypothyroidism. Moreover, the association of symptoms in the patients with NKX2-1 mutations points to an important role of human NKX2-1 in the development and function of thyroid, basal ganglia, and lung, as already described for rodents.

M utations of either PKD1 or PKD2 cause autosomal dominant polycystic kidney disease, a syndrome characterized by extensive formation of renal cysts and progressive renal failure. Homozygous deletion of Pkd1 or Pkd2, the genes encoding polycystin-1 and polycystin-2, disrupt normal renal tubular differentiation in mice but do not affect the early steps of renal development. Here, we show that expression of the C-terminal 112 amino acids of human polycystin-1 triggers branching morphogenesis and migration of inner medullary collecting duct (IMCD) cells, and support in vitro tubule formation. The integrity of the polycystin-2–binding region is necessary but not sufficient to induce branching of IMCD cells. The C-terminal domain of polycystin-1 stimulated protein kinase C-α (PKC-α), but not the extracellular signal–regulated kinases ERK1 or ERK2. Accordingly, inhibition of PKC, but not ERK, prevented polycystin-1–mediated IMCD cell morphogenesis. In contrast, HGF-mediated morphogenesis required ERK activation but was not dependent on PKC. Our findings demonstrate that the C-terminal domain of polycystin-1, acting in a ligand-independent fashion, triggers unique signaling pathways for morphogenesis, and likely plays a central role in polycystin-1 function.

B uffalo/Mna rats spontaneously develop a focal segmental glomerulosclerosis with a histological pattern similar to the human disease. In this study, we investigated the potential of recurrence of the disease by transplantation of normal kidneys into Buffalo/Mna recipients. Kidneys from healthy LEW.1W rats were grafted into proteinuric 6-month-old Buffalo/Mna rats without or with specific tolerance induction following donor-specific transfusion (DST) aimed at controlling host anti-donor immune responses. The inverse combination was carried out to determine whether a proteinuric Buffalo/Mna kidney can recover its permselectivity in a normal environment. As a control, LEW.1W kidneys were grafted into Wistar Furth recipients. After transplantation without DST, recurrence of proteinuria in LEW.1W kidneys appeared at approximately 10 days, possibly associated with rejection of the graft. In the same combination with DST, proteinuria occurred after 20 days, and the attendant glomerular damage suggested that the initial kidney disease had recurred. Transplanted control animals remained free of proteinuria. In the opposite combination, the proteinuria and the lesions of Buffalo/Mna kidneys regressed after transplantation into healthy LEW.1W rats. The recurrence of proteinuria after transplantation in Buffalo/Mna and the remission of lesions in Buffalo/Mna kidneys transplanted into normal hosts suggests that Buffalo/Mna rats express circulating albuminuric factors, which may be relevant to the relapse of idiopathic nephrotic syndrome in humans.

T he ε isoform of protein kinase C (PKCε) is a member of the PKC family of serine/threonine kinases and plays a critical role in protection against ischemic injury in multiple organs. Functional proteomic analyses of PKCε signaling show that this isozyme forms multiprotein complexes in the heart; however, the precise signaling mechanisms whereby PKCε orchestrates cardioprotection are poorly understood. Here we report that Lck, a member of the Src family of tyrosine kinases, forms a functional signaling module with PKCε. In cardiac cells, PKCε interacts with, phosphorylates, and activates Lck. In vivo studies showed that cardioprotection elicited either by cardiac-specific transgenic activation of PKCε or by ischemic preconditioning enhances the formation of PKCε-Lck modules. Disruption of these modules, via ablation of the Lck gene, abrogated the infarct-sparing effects of these two forms of cardioprotection, indicating that the formation of PKCε-Lck signaling modules is required for the manifestation of a cardioprotective phenotype. These findings demonstrate, for the first time to our knowledge, that the assembly of a module (PKCε-Lck) is an obligatory step in the signal transduction that results in a specific phenotype. Thus, PKCε-Lck modules may serve as novel therapeutic targets for the prevention of ischemic injury.

R ecently it has been postulated that mitochondrial ATP-sensitive K⁺ (mitoK_ATP) channels rather than sarcolemmal K_ATP (sarcK_ATP) channels are important as end effectors and/or triggers of ischemic preconditioning (IPC). To define the pathophysiological significance of sarcK_ATP channels, we conducted functional experiments using Kir6.2-deficient (KO) mice. Metabolic inhibition with glucose-free, dinitrophenol-containing solution activated sarcK_ATP current and shortened the action potential duration in ventricular cells isolated from wild-type (WT) but not KO mice. MitoK_ATP channel function was preserved in KO ventricular cells. In anesthetized mice, IPC reduced the infarct size in WT but not KO mice. Following global ischemia/reperfusion, the increase of left ventricular end-diastolic pressure during ischemia was more marked, and the recovery of contractile function was worse, in KO hearts than in WT hearts. Treatment with HMR1098, a sarcK_ATP channel blocker, but not 5-hydroxydecanoate, a mitoK_ATP channel blocker, produced a deterioration of contractile function in WT hearts comparable to that of KO hearts. These findings suggest that sarcKATP channels figures prominently in modulating ischemia/reperfusion injury in the mouse. The rapid heart rate of the mouse (>600 beats per minute) may magnify the relative importance of sarcK_ATP channels during ischemia, prompting caution in the extrapolation of the conclusions to larger mammals.

A b-mediated mechanisms have been considered the major causes of glomerulonephritis (GN). However, recent studies suggest that T cells may be more important in mediating GN. To investigate the effects of antigen-specific CD4⁺ T cells, we generated Th1 cell lines specific for this antigen from rats that had been immunized with a recombinant form of the glomerular basement membrane (GBM) antigen, Col4α3NC1. Upon the transfer of in vitro–activated T cell lines to pertussis toxin-primed, naive syngeneic rats, the recipients developed severe proteinuria/albuminuria, which plateaued after ∼35 days. Although no IgG binding to GBM or C3 deposition could be detected by immunofluorescence, five out of eleven rats exhibited severe GN, as judged by the formation of characteristic crescent-shaped lesions in the glomerluli, whereas the others exhibited modest GN. Thus Col4α3NC1-specific T cells directly initiated glomerular injury in the recipients. One notable difference from GN induced by active immunization was a T cell infiltration in the renal interstitium, which affected some tubules. We therefore injected fluorescence-labeled Col4α3NC1-specific into naive rats, and we found that they were enriched 4.5-fold in the kidney cortex relative to nonspecific control T cells 24 hours later. Many of the T cells were located in the Bowman’s space and had a flattened shape, suggesting that the primary target for the T cells was in or adjacent to the Bowman’s capsule.

O verload of pancreatic β cells in conditions such as hyperglycemia, obesity, and long-term treatment with sulfonylureas leads to β cell exhaustion and type 2 diabetes. Because β cell mass declines under these conditions, apparently as a result of apoptosis, we speculated that overload kills β cells as a result of endoplasmic reticulum (ER) stress. The Akita mouse, which carries a conformation-altering missense mutation (Cys96Tyr) in Insulin 2, likewise exhibits hyperglycemia and a reduced β cell mass. In the development of diabetes in Akita mice, mRNAs for the ER chaperone Bip and the ER stress–associated apoptosis factor Chop were induced in the pancreas. Overexpression of the mutant insulin in mouse MIN6 β cells induced Chop expression and led to apoptosis. Targeted disruption of the Chop gene delayed the onset of diabetes in heterozygous Akita mice by 8–10 weeks. We conclude that ER overload in β cells causes ER stress and leads to apoptosis via Chop induction. Our findings suggest a new therapeutic approach for preventing the onset of diabetes by inhibiting Chop induction or by increasing chaperone capacity in the ER.

T he congenital polycystic kidney (cpk) mutation is the most extensively characterized mouse model of polycystic kidney disease (PKD). The renal cystic disease is fully expressed in homozygotes and is strikingly similar to human autosomal recessive PKD (ARPKD), whereas genetic background modulates the penetrance of the corresponding defect in the developing biliary tree. We now describe the positional cloning, mutation analysis, and expression of a novel gene that is disrupted in cpk mice. The cpk gene is expressed primarily in the kidney and liver and encodes a hydrophilic, 145–amino acid protein, which we term cystin. When expressed exogenously in polarized renal epithelial cells, cystin is detected in cilia, and its expression overlaps with polaris, another PKD-related protein. We therefore propose that the single epithelial cilium is important in the functional differentiation of polarized epithelia and that ciliary dysfunction underlies the PKD phenotype in cpk mice.

T he vasculoprotective effects of sex hormones, particularly estrogens, have been attributed to their ability to increase the bioavailability of nitric oxide through activation of endothelial nitric oxide synthase (eNOS). To dissect the relative contribution in vivo of eNOS, sex hormones, and their interaction in two complex vascular phenotypes, hypertension and atherosclerosis, we used mice doubly deficient in eNOS and apoE (nnee) or lacking only apoE (NNee). Females and males were gonadectomized at 1 month of age and implanted either with control pellets or pellets releasing 17β-estradiol (E2). Hormonally intact nnee mice have elevated blood pressure (BP) and increased atherosclerosis compared with NNee mice, but on removal of gonads, BP and atherosclerosis decreased significantly in nnee mice but not in NNee mice. Three months of treatment with exogenous E2 dramatically reduced atherosclerosis and significantly lowered BP in both NNee and nnee mice compared with animals treated with control pellets. Thus exogenous E2 has strong BP-lowering and atheroprotective effects in apoE-deficient mice, but eNOS is not essential for either effect. Endogenous sex hormones, on the other hand, cause significant damage to the vasculature in the absence of eNOS, but these effects are overridden by interactions between eNOS and sex hormones.

P revious studies have shown that blockade of LIGHT, a T cell costimulatory molecule belonging to the TNF superfamily, by soluble lymphotoxin β receptor–Ig (LTβR-Ig) inhibits the cytotoxic T lymphocyte (CTL) response to host antigenic disparities and ameliorates lethal graft-versus-host disease (GVHD) in a B6 to BDF1 mouse model. Here, we demonstrate that infusion of an mAb against CD40 ligand (CD40L) further increases the efficacy of LTβR-Ig, leading to complete prevention of GVHD. We further demonstrate that alloantigen-specific CTLs become anergic upon rapid expansion, and persist in the tolerized mice as a result of costimulatory blockade. Transfer of anergic CTLs to secondary F1 mice fails to induce GVHD despite the fact that anergic CTLs can be stimulated to proliferate in vitro by antigens and cytokines. Our study provides a potential new approach for the prevention of lethal GVHD.