Depletion of SAM leading to loss of heterochromatin drives muscle stem cell ageing

The global loss of heterochromatin during ageing has been observed in eukaryotes from yeast to humans, and this has been proposed as one of the causes of ageing. However, the cause of this age-associated loss of heterochromatin has remained enigmatic. Here we show that heterochromatin markers, including histone H3K9 di/tri-methylation and HP1, decrease with age in muscle stem cells (MuSCs) as a consequence of the depletion of the methyl donor S-adenosylmethionine (SAM). We find that restoration of intracellular SAM in aged MuSCs restores heterochromatin content to youthful levels and rejuvenates age-associated features, including DNA damage accumulation, increased cell death, and defective muscle regeneration. SAM is not only a methyl group donor for transmethylation, but it is also an aminopropyl donor for polyamine synthesis. Excessive consumption of SAM in polyamine synthesis may reduce its availability for transmethylation. Consistent with this premise, we observe that perturbation of increased polyamine synthesis by inhibiting spermidine synthase restores intracellular SAM content and heterochromatin formation, leading to improvements in aged MuSC function and regenerative capacity in male and female mice. Together, our studies demonstrate a direct causal link between polyamine metabolism and epigenetic dysregulation during murine MuSC ageing.

A randomized trial of hypothesis-driven vs screening neurologic examination

OBJECTIVE

We hypothesized that trainees would perform better using a hypothesis-driven rather than a traditional screening approach to the neurologic examination.

METHODS

We randomly assigned 16 medical students to perform screening examinations of all major aspects of neurologic function or hypothesis-driven examinations focused on aspects suggested by the history. Each student examined 4 patients, 2 of whom had focal deficits. Outcomes of interest were the correct identification of patients with focal deficits, number of specific deficits detected, and examination duration. Outcomes were assessed by an investigator blinded to group assignments. The McNemar test was used to compare the sensitivity and specificity of the 2 examination methods.

RESULTS

Sensitivity was higher with hypothesis-driven examinations than with screening examinations (78% vs 56%; p = 0.046), although specificity was lower (71% vs 100%; p = 0.046). The hypothesis-driven group identified 61% of specific examination abnormalities, whereas the screening group identified 53% (p = 0.008). Median examination duration was 1 minute shorter in the hypothesis-driven group (7.0 minutes vs 8.0 minutes; p = 0.13).

CONCLUSIONS

In this randomized trial comparing 2 methods of neurologic examination, a hypothesis-driven approach resulted in greater sensitivity and a trend toward faster examinations, at the cost of lower specificity, compared with the traditional screening approach. Our findings suggest that a hypothesis-driven approach may be superior when the history is concerning for an acute focal neurologic process.

Canine and feline pregnancy loss due to viral and non-infectious causes: a review

Among the causes for pregnancy loss, viruses and non-infectious factors are among the most important. In both dogs and cats, research and clinical evidence provide proof that there is an increasing incidence of pregnancy loss associated with infectious diseases like herpesvirus, as well as the presence of toxicants or chemicals in the animal's diet and environment. Endocrine causes must be taken into consideration when dealing with pregnancy loss. This review will cover the most recent knowledge regarding viral and non-infectious of pregnancy losses in the dog and cat.

Mucometra, cystic endometrial hyperplasia, and pyometra in the bitch: advances in treatment and assessment of future reproductive success

Pyometra is a common reproductive disorder which affects nearly one fourth of all female dogs before they reach 10 y of age. An association between pyometra and the most common uterine disease of the bitch, cystic endometrial hyperplasia, has been established, as the latter allows commensal bacteria originating from the vagina to proliferate in the uterus at the end of estrus. The progressive degenerative process in the development of cystic endometrial hyperplasia is usually proposed as the initiating lesion for pyometra in bitches; this is mediated by progesterone and potentially aggravated by estrogens. However, a separate process caused by local uterine irritation to trophoblastic reaction and bacterial proliferation has been recently proposed as an alternate mechanism leading to the development of pyometra. Pyometra is clinically distinct in pathogenesis, signs, treatment and prognosis from postpartum metritis or mucometra. Treatment of pyometra has historically involved ovariohysterectomy, however, during the last 10 y, numerous effective treatments have been proposed to treat both open and closed cervix pyometra with good success and future fertility. Among the treatments available, the use of repeated low doses of prostaglandins alone or in association with either dopamine agonists or progesterone-receptor antagonists has been demonstrated to be a viable alternative for valuable breeding dogs.