Genetic disruption of zebrafish mab21l1 reveals a conserved role in eye development and affected pathways

BACKGROUND

The male-abnormal 21 like (MAB21L) genes are important in human ocular development. Homozygous loss of MAB21L1 leads to corneal dystrophy in all affected individuals along with cataracts and buphthalmos in some. The molecular function and downstream pathways of MAB21L factors are largely undefined.

RESULTS

We generated the first mab21l1 zebrafish mutant carrying a putative loss-of-function allele, c.107delA p.(Lys36Argfs*7). At the final stages of embryonic development, homozygous mab21l1c.107delA fish displayed enlarged anterior chambers and corneal thinning which progressed with age. Additional studies revealed increased cell death in the mutant corneas, transformation of the cornea into a skin-like epithelium, and progressive lens degeneration with development of fibrous masses in the anterior chamber. RNA-seq of wild-type and mutant ocular transcriptomes revealed significant changes in expression of several genes, including irf1a and b, stat1, elf3, krt17, tlr9, and loxa associated with immunity and/or corneal function. Abnormal expression of lysyl oxidases have been previously linked with corneal thinning, fibrosis, and lens defects in mammals, suggesting a role for loxa misexpression in the progressive mab21l1c.107delA eye phenotype.

CONCLUSIONS

Zebrafish mab21l1 is essential for normal corneal development, similar to human MAB21L1. The identified molecular changes in mab21l1c.107delA mutants provide the first clues about possible affected pathways.

Ultrasonography patterns of atopic dermatitis in children

BACKGROUND

Atopic dermatitis (AD) is one of the most common allergic diseases in children. The aim of the study was to evaluate the ultrasound picture of lesional and non-lesional skin in children with AD.

MATERIALS AND METHODS

The study included a group of children with AD and a control group. Inclusion criteria were as follows: age 0-8 years and clinical diagnosis of AD. An ultrasound scanner with a 75 MHz transducer probe was used to produce B-mode skin images in lesions and non-lesional skin. The thickness and the echogenicity of epidermis, dermis, and subepidermal low-echogenic band (SLEB) were measured, and the ratio coefficient per body site was calculated.

RESULTS

Ultrasonography of non-lesional skin in children with AD showed uneven epidermis contour, a tendency to increased epidermis and decreased dermis thickness, and the SLEB was observed in 77% of cases. In lesions, there was an increased thickness and a decreased echogenicity of epidermis and dermis, and epidermis had irregular contours in most cases. The SLEB was in all lesions, showing greater thickness and lower echogenicity compared with non-lesional skin.

CONCLUSION

HF-USG of the skin allows visualizing the epidermal barrier disruption and inflammation in dermis in children with AD on the entire surface of the skin.

Insulin Protects Cortical Neurons Against Glutamate Excitotoxicity

Glutamate excitotoxicity is implicated in the pathogenesis of numerous diseases, such as stroke, traumatic brain injury, and Alzheimer's disease, for which insulin resistance is a concomitant condition, and intranasal insulin treatment is believed to be a promising therapy. Excitotoxicity is initiated primarily by the sustained stimulation of ionotropic glutamate receptors and leads to a rise in intracellular Ca²⁺ ([Ca²⁺] _i ), followed by a cascade of intracellular events, such as delayed calcium deregulation (DCD), mitochondrial depolarization, adenosine triphosphate (ATP) depletion that collectively end in cell death. Therefore, cross-talk between insulin and glutamate signaling in excitotoxicity is of particular interest for research. In the present study, we investigated the effects of short-term insulin exposure on the dynamics of [Ca²⁺] _i and mitochondrial potential in cultured rat cortical neurons during glutamate excitotoxicity. We found that insulin ameliorated the glutamate-evoked rise of [Ca²⁺] _i and prevented the onset of DCD, the postulated point-of-no-return in excitotoxicity. Additionally, insulin significantly improved the glutamate-induced drop in mitochondrial potential, ATP depletion, and depletion of brain-derived neurotrophic factor (BDNF), which is a critical neuroprotector in excitotoxicity. Also, insulin improved oxygen consumption rates, maximal respiration, and spare respiratory capacity in neurons exposed to glutamate, as well as the viability of cells in the MTT assay. In conclusion, the short-term insulin exposure in our experiments was evidently a protective treatment against excitotoxicity, in a sharp contrast to chronic insulin exposure causal to neuronal insulin resistance, the adverse factor in excitotoxicity.

Relative deficiency of acidic isoforms of osteopontin from stone former urine

We have tested the relative electrophoretic mobility of osteopontin (OPN) isolated from urine obtained from normal individuals (NU) against similar samples derived from the urine of stone formers (SFU) using high-resolution isoelectric focusing (isoelectric point, pI range 3.5-4.5) in 2D electrophoresis, with Western blot detection. We also report the results from competitive ELISA analyses of these samples. We demonstrated that human urinary OPN has a discrete four band separation pattern that conforms to four previously documented OPN isoforms. The lower two M(r) isoforms migrate to a greater degree toward the acidic end of the gel than do the higher two M(r) isoforms. Densitometry of the signal reveals significant difference in the migration pattern of OPN from SFU as compared to that from NU based on an analysis of the spot intensities grouped in 0.1 pI unit increments. A novel method for the calculation of a weight-averaged pI based on the relative signal strength in an OPN 2D Western blot was developed. The analysis revealed a significantly increased weight-averaged pI values for the higher M(r) forms of OPN in the stone former compared to normal population. Additionally, alkaline phosphatase-treated NU samples resulted in a significant average pI shift of 0.05 units in the alkaline direction, suggesting that a decrease in the average degree of phosphorylation could be responsible for the difference between NU and SFU pI.

Peroxiredoxin 6 phosphorylation and subsequent phospholipase A2 activity are required for agonist-mediated activation of NADPH oxidase in mouse pulmonary microvascular endothelium and alveolar macrophages

Peroxiredoxin 6 (Prdx6), a bifunctional enzyme with glutathione peroxidase and phospholipase A2 (PLA(2)) activities, participates in the activation of NADPH oxidase 2 (NOX2) in neutrophils, but the mechanism for this effect is not known. We now demonstrate that Prdx6 is required for agonist-induced NOX2 activation in pulmonary microvascular endothelial cells (PMVEC) and that the effect requires the PLA(2) activity of Prdx6. Generation of reactive oxygen species (ROS) in response to angiotensin II (Ang II) or phorbol 12-myristate 13-acetate was markedly reduced in perfused lungs and isolated PMVEC from Prdx6 null mice. Rac1 and p47(phox), cytosolic components of NOX2, translocated to the endothelial cell membrane after Ang II treatment in wild-type but not Prdx6 null PMVEC. MJ33, an inhibitor of Prdx6 PLA(2) activity, blocked agonist-induced PLA(2) activity and ROS generation in PMVEC by >80%, whereas inhibitors of other PLA(2)s were ineffective. Transfection of Prx6 null cells with wild-type and C47S mutant Prdx6, but not with mutants of the PLA(2) active site (S32A, H26A, and D140A), "rescued" Ang II-induced PLA(2) activity and ROS generation. Ang II treatment of wild-type cells resulted in phosphorylation of Prdx6 and its subsequent translocation from the cytosol to the cell membrane. Phosphorylation as well as PLA(2) activity and ROS generation were markedly reduced by the MAPK inhibitor, U0126. Thus, agonist-induced MAPK activation leads to Prdx6 phosphorylation and translocation to the cell membrane, where its PLA(2) activity facilitates assembly of the NOX2 complex and activation of the oxidase.

C3G overexpression in glomerular epithelial cells during anti-GBM-induced glomerulonephritis

The guanine nucleotide exchange factor C3G, along with the CrkII adaptor protein, mediates GTP activation of the small GTPase proteins Rap1 and R-Ras, facilitating their activation of downstream signaling pathways, which had been found to be important in the pathogenesis of glomerulonephritis. We found that expression of C3G protein was upregulated in glomerular epithelial cells in an experimental model of accelerated anti-GBM antibody-induced glomerulonephritis expression. To determine the consequence of its increased expression, we transfected C3G (using adenoviral constructs) into cultured glomerular epithelial cells and measured the activated forms (i.e., GTP-bound) forms of Rap1 and R-Ras. Activation of Rap1 was not affected by C3G; however, the basal level of GTP-bound R-Ras was decreased. Further, C3G over-expression enhanced the activation of R-Ras in response to endothelin. Overexpression of C3G also led to a significant reduction in glomerular epithelial cell spreading and decreased the cells' E-cadherin expression and augmented their migration. We found that C3G was overexpressed in accelerated anti-GBM antibody-induced glomerulonephritis and suggest that this modulates glomerular epithelial cell morphology and behavior.

Functional analysis of human mutations in homeodomain transcription factor PITX3

BACKGROUND

The homeodomain-containing transcription factor PITX3 was shown to be essential for normal eye development in vertebrates. Human patients with point mutations in PITX3 demonstrate congenital cataracts along with anterior segment defects in some cases when one allele is affected and microphthalmia with brain malformations when both copies are mutated. The functional consequences of these human mutations remain unknown.

RESULTS

We studied the PITX3 mutant proteins S13N and G219fs to determine the type and severity of functional defects. Our results demonstrate alterations in DNA-binding profiles and/or transactivation activities and suggest a partial loss-of-function in both mutants with the G219fs form being more severely affected. No anomalies in cellular distribution and no dominant-negative effects were discovered for these mutants. Interestingly, the impairment of the G219fs activity varied between different ocular cell lines.

CONCLUSION

The G219fs mutation was found in multiple families affected with congenital cataracts along with anterior segment malformations in many members. Our data suggest that the presence/severity of anterior segment defects in families affected with G219fs may be determined by secondary factors that are expressed in the developing anterior segment structures and may modify the effect(s) of this mutation. The S13N mutant showed only minor alteration of transactivation ability and DNA binding pattern and may represent a rare polymorphism in the PITX3 gene. A possible contribution of this mutation to human disease needs to be further investigated.

CrkIII: a novel and biologically distinct member of the Crk family of adaptor proteins

As the role for adaptor proteins constantly proliferates, appreciation of their importance has never been higher. The Crk family of adaptor proteins is no exception. Currently comprising four members, v-Crk, CrkI, CrkII and Crk-like protein, we have introduced a fifth member, CrkIII. Cloned by the CORT technique, CrkIII is identical in sequence to CrkII until the second of its two SH3 domains, which is disrupted partway through and results in a nonfunctional domain and a unique C-terminal sequence. We have demonstrated the existence of native CrkIII at the message level using RT-PCR and RNAse protection assays, and at the protein level in mouse fibroblasts. We show that CrkII overexpression is capable of enhancing insulin-stimulated ERK activity, whereas CrkIII is not, thus partially characterizing a novel member of the Crk family and elucidating important effects mediated by the c-terminal SH3 domain.

Li+ protects nerve cells against destabilization of Ca2+ homeostasis and delayed death caused by removal of external Na+

In experiments with fura-2 loaded cultured rat cerebellar granule cells we have compared the changes in [Ca2+]i homeostasis produced by replacement of external Na+ with the organic cation N-methyl-D-glucamine (NMDG) or Li+. The Na+/NMDG replacement caused an increase in baseline [Ca2+]i and a considerable delay in [Ca2+]i recovery following a glutamate (Glu) pulse in almost all the cells. In contrast Na+/Li+ replacement usually did not change baseline [Ca2+]i and produced only a small (if any) delay in the post-glutamate [Ca2+]i recovery. Previously [Storozhevykh et al. (1998) FEBS Lett. 431, 215-218] we revealed that perturbation of [Ca2+]i homeostasis caused by Na+/NMDG replacement cannot be explained by a reversal of the Na+/Ca2+ exchange but is mainly due to Ca2+ influx through NMDA channels activated by Na+ dependent release of endogenous excitatory amino acids ('reversed Glu uptake'). In the present work we confirmed this conclusion and obtained evidence suggesting that in contrast to NMDG Li+ interferes with the 'reversed Glu uptake' triggered by removal of external Na+. Thus it has been shown that the addition of Li+ (20 mM) to a Na+-free NMDG-containing solution suppressed both the perturbation of [Ca2+]i homeostasis and delayed neuronal death caused by Na+/NMDG replacement. Li+ is also able to abolish the [Ca2+]i response induced by PDC which at high concentrations (> 200 microM) is shown to stimulate the release of endogenous Glu. In contrast to Na+/Li+, Na+/NMDG replacement greatly enhances [Ca2+]i increase caused by PDC. Control experiments showed that Na+/Li+ replacement does not decrease the [Ca2+]i response to the Glu pulse. Therefore we concluded that a considerable quantitative difference between the effects of Na+/NMDG and Na+/Li+ replacements on both [Ca2+]i homeostasis and cell viability resulted mainly from the ability of Li+ to attenuate the release of endogenous Glu in response to the removal of external Na+.

Role of Na+/Ca2+ exchange in regulation of neuronal Ca2+ homeostasis requires re-evaluation

In cultured rat cerebellar granule cells an inhibition of plasma membrane Na+/Ca2+ exchange by removal of external Na+ (replacement with NMDG) caused an increase in [Ca2+]i at rest and a considerable delay in [Ca2+]i recovery from Glu-imposed [Ca2+]i load. These effects did not result from Ca2+ influx through reversed Na+/Ca2+ exchange since they were readily abolished or prevented by using the NMDA receptor inhibitor AP-5 (100 microM) or the NMDA channel blocker memantine (25-50 microM). The effect of Na+/NMDG replacement could be enhanced by: (1) an increase in cytoplasmic Na+ concentration by monensin pretreatment of neurons; (2) external alkalinity, pH 8.5; (3) blockade of the mitochondrial Ca2+ uptake with antimycin plus oligomycin. Analysis of the data obtained led us to conclude that all the changes in [Ca2+]i caused by Na+/NMDG replacement are mainly due to a release of endogenous Glu (reversed Glu uptake) and a subsequent Ca2+ influx through NMDA receptor-mediated channels.