Protocol endomyocardial biopsy beyond 6 months-It is time to move on.

The optimal duration and frequency of routine surveillance endomyocardial biopsy (EMB) have been questioned in the current era of heart transplantation (HT), where the advances in immunosuppression and donor selection strategies have led to a decline in acute allograft rejection. We investigated the utility of routine EMB beyond 6 months post-HT. A single-center retrospective review was performed on 2963 EMBs from 220 HT recipients over 10 years. Each EMB was categorized into protocol or symptom-triggered biopsy and reviewed for rejection. Heart transplant recipients with ≥2 known risk factors for rejection were designated as an elevated risk group. The majority of rejections occurred within 3 months following HT. The yield of routine protocol EMBs was significantly lower than symptom-triggered EMBs, not only during the first 6 months post-HT (1.6% vs. 33.3%, P < .0001), but more so during the 6-12 months (0.1% vs 83.0%, P < .0001). A similar pattern was observed in heart transplant recipients at both elevated and standard risk for rejection. In conclusion, EMB was found to be a low-yield screening modality for rejection beyond 6 months post-HT.

Functional characterization of an AQP0 missense mutation, R33C, that causes dominant congenital lens cataract, reveals impaired cell-to-cell adhesion.

Aquaporin 0 (AQP0) performs dual functions in the lens fiber cells, as a water pore and as a cell-to-cell adhesion molecule. Mutations in AQP0 cause severe lens cataract in both humans and mice. An arginine to cysteine missense mutation at amino acid 33 (R33C) produced congenital autosomal dominant cataract in a Chinese family for five generations. We re-created this mutation in wild type human AQP0 (WT-AQP0) cDNA by site-directed mutagenesis, and cloned and expressed the mutant AQP0 (AQP0-R33C) in heterologous expression systems. Mutant AQP0-R33C showed proper trafficking and membrane localization like WT-AQP0. Functional studies conducted in Xenopus oocytes showed no significant difference (P > 0.05) in water permeability between AQP0-R33C and WT-AQP0. However, the cell-to-cell adhesion property of AQP0-R33C was significantly reduced (P < 0.001) compared to that of WT-AQP0, indicated by cell aggregation and cell-to-cell adhesion assays. Scrape-loading assay using Lucifer Yellow dye showed reduction in cell-to-cell adhesion affecting gap junction coupling (P < 0.001). The data provided suggest that this mutation might not have caused significant alterations in protein folding since there was no obstruction in protein trafficking or water permeation. Reduction in cell-to-cell adhesion and development of cataract suggest that the conserved positive charge of Extracellular Loop A may play an important role in bringing fiber cells closer. The proposed schematic models illustrate that cell-to-cell adhesion elicited by AQP0 is vital for lens transparency and homeostasis.