Cathepsin B increases ENaC activity leading to hypertension early in nephrotic syndrome

The NPHS2 gene, encoding the slit diaphragm protein podocin, accounts for genetic and sporadic forms of nephrotic syndrome (NS). Patients with NS often present symptoms of volume retention, such as oedema formation or hypertension. The primary dysregulation in sodium handling involves an inappropriate activation of the epithelial sodium channel, ENaC. Plasma proteases in a proteinuria‐dependent fashion have been made responsible; however, referring to the timeline of symptoms occurring and underlying mechanisms, contradictory results have been published. Characterizing the mouse model of podocyte inactivation of NPHS2 (Nphs2^?pod) with respect to volume handling and proteinuria revealed that sodium retention, hypertension and gross proteinuria appeared sequentially in a chronological order. Detailed analysis of Nphs2^?pod during early sodium retention, revealed increased expression of full‐length ENaC subunits and αENaC cleavage product with concomitant increase in ENaC activity as tested by amiloride application, and augmented collecting duct Na⁺/K⁺‐ATPase expression. Urinary proteolytic activity was increased and several proteases were identified by mass spectrometry including cathepsin B, which was found to process αENaC. Renal expression levels of precursor and active cathepsin B were increased and could be localized to glomeruli and intercalated cells. Inhibition of cathepsin B prevented hypertension. With the appearance of gross proteinuria, plasmin occurs in the urine and additional cleavage of γENaC is encountered. In conclusion, characterizing the volume handling of Nphs2^?pod revealed early sodium retention occurring independent to aberrantly filtered plasma proteases. As an underlying mechanism cathepsin B induced αENaC processing leading to augmented channel activity and hypertension was identified.     

Direct Cloning of Human 10q25 Neocentromere DNA Using Transformation-Associated Recombination (TAR) in Yeast

The transformation-associated recombination (TAR) procedure allows rapid, site-directed cloning of specific human chromosomal regions as yeast artificial chromosomes (YACs). The procedure requires knowledge of only a single, relatively small genomic sequence that resides adjacent to the chromosomal region of interest. We applied this approach to the cloning of the neocentromere DNA of a marker chromosome that we have previously shown to have originated through the activation of a latent centromere at human chromosome 10q25. Using a unique 1.4-kb DNA fragment as a “hook” in TAR experiments, we achieved single-step isolation of the critical neocentromere DNA region as two stable, 110- and 80-kb circular YACs. For obtaining large quantities of highly purified DNA, these YACs were retrofitted with the yeast–bacteria–mammalian-cells shuttle vector BRV1, electroporated intoEscherichia coliDH10B, and isolated as bacterial artificial chromosomes (BACs). Extensive characterization of these YACs and BACs by PCR and restriction analyses revealed that they are identical to the corresponding regions of the normal chromosome 10 and provided further support for the formation of the neocentromere within the marker chromosome through epigenetic activation.     

A novel strategy for analysis of gene homologues and segmental genome duplications

Transformation-associated recombination (TAR) cloning allows selective isolation of a desired chromosomal region or gene from complex genomes. The method exploits a high level of recombination between homologous DNA sequences during transformation in the yeast Saccharomyces cerevisiae. We investigated the effect of nonhomology on the efficiency of gene capture and found that up to 15% DNA divergence did not prevent efficient gene isolation. Such tolerance to DNA divergence greatly expands the potential applications of TAR cloning for comparative genomics. In this study, we were able to use the technique to isolate nonidentical chromosomal duplications and gene homologues.     

Reduced susceptibility to eccentric exercise-induced muscle damage in resistance-trained men is not linked to resistance training-related neural adaptations

The purpose of this study was to examine the acute effects of maximal concentric vs. eccentric exercise on the isometric strength of the elbow flexor, as well as the biceps brachii muscle electromyographic (EMG) responses in resistance-trained (RT) vs. untrained (UT) men. Thirteen RT men (age: 24 ± 4 years; height: 180.2 ± 7.7 cm; body weight: 92.2 ± 16.9 kg) and twelve UT men (age: 23 ± 4 years; height: 179.2 ± 5.0 cm; body weight: 81.5 ± 8.6 kg) performed six sets of ten maximal concentric isokinetic (CON) or eccentric isokinetic (ECC) elbow flexion exercise in two separate visits. Before and after the exercise interventions, maximal voluntary contractions (MVCs) were performed for testing isometric strength. In addition, bipolar surface EMG signals were detected from the biceps brachii muscle during the strength testing. Both CON and ECC caused isometric strength to decrease, regardless of the training status. However, ECC caused greater isometric strength decline than CON did for the UT group (p = 0.006), but not for the RT group. Both EMG amplitude and mean frequency significantly decreased and increased, respectively, regardless of the training status and exercise intervention. Resistance-trained men are less susceptible to eccentric exercise-induced muscle damage, but this advantage is not likely linked to the chronic resistance training-induced neural adaptations.     

Recovery and potential utility of YACs as circular YACs/BACs

A method has been established to convert pYAC4-based linear yeast artificial chromosomes (YACs) into circular chromosomes that can also be propagated in Escherichia coli cells as bacterial artificial chromosomes (BACs). The circularization is based on use of a vector that contains a yeast dominant selectable marker (G418R), a BAC cassette and short targeting sequences adjacent to the edges of the insert in the pYAC4 vector. When it is introduced into yeast, the vector recombines with the YAC target sequences to form a circular molecule, retaining the insert but discarding most of the sequences of the YAC telomeric arms. YACs up to 670 kb can be efficiently circularized using this vector. Re-isolation of megabase-size YAC inserts as a set of overlapping circular YAC/BACs, based on the use of an Alu-containing targeting vector, is also described. We have shown that circular DNA molecules up to 250 kb can be efficiently and accurately transferred into E.coli cells by electroporation. Larger circular DNAs cannot be moved into bacterial cells, but can be purified away from linear yeast chromosomes. We propose that the described system for generation of circular YAC derivatives can facilitate sequencing as well as functional analysis of genomic regions.