Impact of Atrial Fibrillation and Sinus Rhythm Restoration on Reticulated Platelets.

OBJECTIVE: To assess the impact of nonvalvular atrial fibrillation (NVAF) and sinus rhythm restoration on the distribution of reticulated platelets (RPs), which are known to be associated with thrombotic propensity and have a greater predilection for thrombus participation. PARTICIPANTS AND METHODS: The RP content was assessed by flow cytometry (thiazole orange/CD61) in 110 consecutive patients with NVAF before and 3 to 4 months after catheter ablation of the pulmonary veins. Results were compared with those of 55 age- and sex-matched controls with normal sinus rhythm. RESULTS: The mean ± SD percentage of RPs was higher in patients with NVAF compared with controls (28.5%±7.3% vs 6.4%±5.3%; P<.001). The RP content did not vary by CHA2DS2-VASc score. After catheter ablation of the pulmonary veins, 63 patients were available for follow-up assessment. A significant reduction of RPs was observed compared with preintervention values (29.85%±7.1% vs 20.79%±7.6%; P<.001). During follow-up, 19% of patients (12 of 63) had confirmed AF recurrence. The mean ± SD percentage of RPs was higher in this group than in those without a recurrence (24.7%±6.5% vs 18.9%±7.5%; P=.01). CONCLUSION: Nonvalvular atrial fibrillation affects the percentage of RPs, independent of the CHA2DS2-VASc score. After ablation, RP content dropped significantly. High RP content in patients with NVAF may explain the potential mechanism of thromboembolic complications and the lack of efficacy of currently available antiplatelet therapy for stroke prevention in this dysrhythmia.

The transmembrane protein meckelin (MKS3) is mutated in Meckel-Gruber syndrome and the wpk rat.

Meckel-Gruber syndrome is a severe autosomal, recessively inherited disorder characterized by bilateral renal cystic dysplasia, developmental defects of the central nervous system (most commonly occipital encephalocele), hepatic ductal dysplasia and cysts and polydactyly. MKS is genetically heterogeneous, with three loci mapped: MKS1, 17q21-24 (ref. 4); MKS2, 11q13 (ref. 5) and MKS3 (ref. 6). We have refined MKS3 mapping to a 12.67-Mb interval (8q21.13-q22.1) that is syntenic to the Wpk locus in rat, which is a model with polycystic kidney disease, agenesis of the corpus callosum and hydrocephalus. Positional cloning of the Wpk gene suggested a MKS3 candidate gene, TMEM67, for which we identified pathogenic mutations for five MKS3-linked consanguineous families. MKS3 is a previously uncharacterized, evolutionarily conserved gene that is expressed at moderate levels in fetal brain, liver and kidney but has widespread, low levels of expression. It encodes a 995-amino acid seven-transmembrane receptor protein of unknown function that we have called meckelin.

Development of multiorgan pathology in the wpk rat model of polycystic kidney disease.

Rodent models of polycystic kidney disease (PKD) have provided valuable insight into the cellular changes associated with cystogenesis in humans. The present study characterizes the morphology of renal and extrarenal pathology of autosomal recessive PKD induced by the wpk gene in Wistar rats. In wpk(-/-) rats, proximal tubule and collecting duct cysts develop in utero and eventually consume the kidney. Increased apoptosis, mitosis, and extracellular tenascin deposition parallel cyst development. Extrarenal pathology occurs in the immune system (thymic and splenic hypoplasia) and central nervous system (CNS; hypoplasia to agenesis of the corpus callosum with severe hydrocephalus). Severity of hydrocephalus varied inversely with size of the corpus callosum. In wpk(-/-) rats, the corpus callosum exhibits relatively few axons that cross the midline. This CNS pathology is similar to that described in three human renal cystic syndromes: orofaciodigital, genitopatellar, and cerebrorenal-digital syndromes. Collecting duct and ventricular ependymal cilia appear morphologically normal. To determine if rodent background strain and the presence of modifier genes affect severity of the disease, we crossed the Wistar-wpk rat with Brown Norway (BN) and Long Evan (LE) rats and found the degree of renal and cerebral pathology was diminished as evidenced by lower kidney weight as a percent of body weight and serum urea nitrogen concentration in cystic rats on LE or BN strains as well as less prominent cranial enlargement. Crosses with BN rats allowed us to localize the wpk gene on chromosome 5 very close to the D5Rat73 marker. The wpk gene lies within a chromosomal region known to harbor a PKD modifier locus. In summary, the types of renal and cerebral pathology seen in the Wistar wpk rat are a unique combination seen only in this rodent model.

Cellular and subcellular localization of the ARPKD protein; fibrocystin is expressed on primary cilia.

Autosomal recessive polycystic kidney disease (ARPKD) is an infantile form of PKD characterized by fusiform dilation of collecting ducts and congenital hepatic fibrosis. The ARPKD gene, PKHD1, is large (approximately 470 kb; 67 exons) with a 12222 bp longest open reading frame, although multiple different splice forms may be generated. The predicted full-length ARPKD protein, fibrocystin, is membrane bound with 4074 amino acids (447 kDa molecular weight). To characterize the pattern of fibrocystin expression we have generated four monoclonal antibodies (mAb) to the cytoplasmic tail of the protein. Western analysis of human kidney membrane protein showed an identical pattern with each mAb; a strongly expressing large product (>450 kDa), consistent with the predicted protein size, and a weaker approximately 220 kDa band. The same large product was detected in rat and mouse kidney with lower level expression in liver. To further show that these mAbs recognize fibrocystin, tissue from ARPKD patients was analyzed and no fibrocystin products were detected. Immunohistochemical analysis of the developing kidney showed expression in the branching ureteric bud and collecting ducts, expression that persisted into adulthood. Biliary duct staining was found in the liver, plus staining in the pancreas and developing testis. Immunofluorescence analysis of MDCK cells showed a major site of expression in the primary cilia. Recent studies have associated the disease protein in various human and animal forms of PKD with cilia. The localization of fibrocystin to cilia further strengthens that correlation and indicates that the primary defect in ARPKD may be linked to ciliary dysfunction.