Learning during middle age: a resistance to stress?

Acute stressful experience enhances subsequent learning in males and impairs learning in females. These sex differences emerge soon after puberty in adulthood. Whether these opposite effects of stress on learning extend into older age is unknown. To examine this, young adult (2-3 months) and middle aged (17-18 months) Fischer 344 rats of both sexes were exposed to an acute stressor of brief tailshocks and trained 24 h later with classical eyeblink conditioning using a trace paradigm. Whereas stressful experience enhanced conditioning in adult males and impaired conditioning in adult females, it had no effect whatsoever on conditioning in the aging animals of either sex. There was no effect of aging itself on acquisition of the conditioned response, suggesting that trace conditioning is not necessarily compromised during this period of life. Together, these data indicate that associative learning in the aging animal is resistant to both the negative and positive consequences of stressful experience.     

Comprehensive approach to high-resolution KIR typing

Multiple studies suggest that prospective KIR typing may be beneficial for the outcome of bone marrow transplants, but to date no practical high-resolution KIR typing system has been developed. Here we propose a comprehensive high-resolution typing approach that provides allele level KIR typing. Based on the low-resolution typing obtained by SSO, the 14 KIR loci are divided in groups according to the level of polymorphism in exons coding for extracellular Ig-like domains and cytoplasmic tail. The first group is typed by sequence-specific oligonucleotide only; the second is typed by sequence-based typing (SBT) based on the amplification of a fragment coding the Ig-like domains; and the third is typed by SBT based on amplification of a fragment coding the cytoplasmic tail. SBT for the fourth group includes both the Ig-like and cytoplasmic domains. Because of a considerable number of polymorphisms scattered throughout all nine KIR exons, SBT results may still produce a number of ambiguities, which can be resolved by sequence-specific primers. This combined high-resolution approach was applied to the complete KIR typing of 205 Caucasian hematopoietic stem cell donors in support of the National Marrow Donor Program High-resolution KIR Typing Pilot Project. High-resolution typing of several KIR loci produced numerous novel alleles, whereas some loci demonstrated very limited polymorphism. Several of the novel alleles appeared in more than four donors, suggesting that these alleles are not rare. Our results showed that the comprehensive KIR typing approach presented here provides the balance of high-resolution typing and cost effectiveness.     

Essential role of Skp2-mediated p27 degradation in growth and adaptive expansion of pancreatic beta cells

Diabetes results from an inadequate mass of functional beta cells, due to either beta cell loss caused by immune assault or the lack of compensation to overcome insulin resistance. Elucidating the mechanisms that regulate beta cell mass has important ramifications for fostering beta cell regeneration and the treatment of diabetes. We report here that Skp2, a substrate recognition component of Skp1-Cul1-F-box (SCF) ubiquitin ligase, played an essential and specific role in regulating the cellular abundance of p27 and was a critical determinant of beta cell proliferation. In Skp2(-/-) mice, accumulation of p27 resulted in enlarged polyploid beta cells as a result of endoreduplication replacing proliferation. Despite beta cell hypertrophy, Skp2(-/-) mice exhibited diminished beta cell mass, hypoinsulinemia, and glucose intolerance. Increased insulin resistance resulting from diet-induced obesity caused Skp2(-/-) mice to become overtly diabetic, because beta cell growth in the absence of cell division was insufficient to compensate for increased metabolic demand. These results indicate that the Skp2-mediated degradation pathway regulating the cellular degradation of p27 is essential for establishing beta cell mass and to respond to increased metabolic demand associated with insulin resistance.     

Staged circumferential and ostial pulmonary vein ablation for the treatment of paroxysmal atrial fibrillation

BACKGROUND: Comparisons between segmental ostial disconnection of the pulmonary veins (PV) and circumferential ablation have produced conflicting results in patients with paroxysmal atrial fibrillation (AF). The aim of this study was to evaluate a staged ablation procedure, every step of which was assessed by means of AF inducibility. METHODS: Twenty-two patients with paroxysmal AF were subjected to three ablation stages during one session: (1) circumferential ablation around the PV ostia, (2) segmental ostial PV isolation, and (3) ablation of areas within the circumferential lines with fractionated electrograms or voltage >0.2 mV as well as linear ablation at the mitral isthmus and the left atrial roof. Endpoint of the procedure was noninducibility of AF at any stage. RESULTS: Average radiofrequency energy delivery, fluoroscopy, and procedure times were 43 +/- 11 minutes, 40 +/- 11 minutes, and 3.8 +/- 0.5 hours, respectively. At 6-months follow-up, four patients experienced recurrence of AF (18%), whereas two additional patients (9%) had left atrial arrhythmias not registered before the procedure. Ninety-five percent of the patients who did not have inducible AF (regardless of the stage of ablation at which noninducibility was achieved) were free of recurrent AF, as opposed to none of the patients in whom AF was inducible at the end of the procedure (log-rank test, P < 0.001). CONCLUSIONS: A staged ablation procedure combing circumferential and ostial PV ablation with AF noninducibilty as endpoint may result in high success rates without the need of prolonged ablation sessions in certain patients with paroxysmal atrial fibrillation.     

Ferroportin in monocytes of hemodialysis patients and its associations with hepcidin,inflammation, markers of iron status and resistance to erythropoietin

Purpose

Disturbed iron homeostasis contributes to resistance to recombinant human erythropoietin (rHuEpo) in hemodialysis (HD) patients. Increased hepcidin, which downregulates the iron exporter ferroportin, has been incriminated. However, other factors also control ferroportin expression in mononuclear phagocyte system. Ferroportin in monocytes, as well as serum hepcidin, interleukin-6 (IL-6) and common markers of iron status were measured and correlations with rHuEpo resistance index (ERI) were evaluated.

Methods

After a 4-week washout period from iron treatment, 34 HD patients and 20 healthy volunteers enrolled in the study. Ferroportin was assessed by means of western blotting, whereas hepcidin and IL-6 with enzyme-linked immunosorbent assay. Hemoglobin, serum iron, ferritin and transferrin saturation (TSAT) were also measured.

Results

Ferroportin in monocytes of HD patients was decreased. Serum hepcidin and IL-6 were increased, whereas serum iron and TSAT were decreased. ERI was negatively correlated with ferroportin and all the markers of iron adequacy, but not with hepcidin.

Conclusion

Decreased ferroportin in monocytes of HD patients accompanies increased hepcidin, inflammation, decreased iron availability and is correlated with resistance to rHuEpo treatment.     

Childhood Bone Mineral Content Is Associated With Methylation Status of the RXRA Promoter at Birth

Maternal vitamin D deficiency has been associated with reduced offspring bone mineral accrual. Retinoid‐X receptor‐alpha (RXRA) is an essential cofactor in the action of 1,25‐dihydroxyvitamin D (1,25[OH]₂‐vitamin D), and RXRA methylation in umbilical cord DNA has been associated with later offspring adiposity. We tested the hypothesis that RXRA methylation in umbilical cord DNA collected at birth is associated with offspring skeletal development, assessed by dual‐energy X‐ray absorptiometry, in a population‐based mother‐offspring cohort (Southampton Women's Survey). Relationships between maternal plasma 25‐hydroxyvitamin D (25[OH]‐vitamin D) concentrations and cord RXRA methylation were also investigated. In 230 children aged 4 years, a higher percent methylation at four of six RXRA CpG sites measured was correlated with lower offspring bone mineral content (BMC) corrected for body size (β = ?2.1 to ?3.4 g/SD, p = 0.002 to 0.047). In a second independent cohort (n = 64), similar negative associations at two of these CpG sites, but positive associations at the two remaining sites, were observed; however, none of the relationships in this replication cohort achieved statistical significance. The maternal free 25(OH)‐vitamin D index was negatively associated with methylation at one of these RXRA CpG sites (β = ?3.3 SD/unit, p = 0.03). Thus, perinatal epigenetic marking at the RXRA promoter region in umbilical cord was inversely associated with offspring size–corrected BMC in childhood. The potential mechanistic and functional significance of this finding remains a subject for further investigation. © 2014 American Society for Bone and Mineral Research.