The nerve growth factor precursor proNGF exhibits neurotrophic activity but is less active than mature nerve growth factor

Nerve growth factor (NGF) promotes neuronal survival and differentiation and stimulates neurite outgrowth. NGF is synthesized as a precursor, proNGF, which undergoes post-translational processing to generate mature beta-NGF. It has been assumed that, in vivo, NGF is largely processed into the mature form and that mature NGF accounts for the biological activity. However, we recently showed that proNGF is abundant in CNS tissues whereas mature NGF is undetectable, suggesting that proNGF has biological functions beyond its role as a precursor. To determine whether proNGF exhibits biological activity, we mutagenized the precursor-processing site and expressed unprocessed, cleavage-resistant proNGF protein in insect cells. Survival and neurite outgrowth assays on murine superior cervical ganglion neurons and PC12 cells indicated that proNGF exhibits neurotrophic activity similar to mature 2.5S NGF, but is approximately fivefold less active. ProNGF binds to the high-affinity receptor, TrkA, as determined by cross-linking to PC12 cells, and is also slightly less active than mature NGF in promoting phosphorylation of TrkA and its downstream signaling effectors, Erk1/2, in PC12 and NIH3T3-TrkA cells. These data, coupled with our previous report that proNGF is the major form of NGF in the CNS, suggest that proNGF could be responsible for much of the biological activity normally attributed to mature NGF in vivo.     

APOBEC3G genetic variants and their influence on the progression to AIDS

The cytosine deaminase APOBEC3G, in the absence of the human immunodeficiency virus type 1 (HIV-1) accessory gene HIV-1 viral infectivity factor (vif), inhibits viral replication by introducing G-->A hypermutation in the newly synthesized HIV-1 DNA negative strand. We tested the hypothesis that genetic variants of APOBEC3G may modify HIV-1 transmission and disease progression. Single nucleotide polymorphisms were identified in the promoter region (three), introns (two), and exons (two). Genotypes were determined for 3,073 study participants enrolled in six HIV-AIDS prospective cohorts. One codon-changing variant, H186R in exon 4, was polymorphic in African Americans (AA) (f = 37%) and rare in European Americans (f < 3%) or Europeans (f = 5%). For AA, the variant allele 186R was strongly associated with decline in CD4 T cells (CD4 slope on square root scale: -1.86, P = 0.009), The 186R allele was also associated with accelerated progression to AIDS-defining conditions in AA. The in vitro antiviral activity of the 186R enzyme was not inferior to that of the common H186 variant. These studies suggest that there may be a modifying role of variants of APOBEC3G on HIV-1 disease progression that warrants further investigation.     

Differential effects of heptanoate and hexanoate on myocardial citric acid cycle intermediates following ischemia-reperfusion.

In the normal heart, there is loss of citric acid cycle (CAC) intermediates that is matched by the entry of intermediates from outside the cycle, a process termed anaplerosis. Previous in vitro studies suggest that supplementation with anaplerotic substrates improves cardiac function during myocardial ischemia and/or reperfusion. The present investigation assessed whether treatment with the anaplerotic medium-chain fatty acid heptanoate improves contractile function during ischemia and reperfusion. The left anterior descending coronary artery of anesthetized pigs was subjected to 60 min of 60% flow reduction and 30 min of reperfusion. Three treatment groups were studied: saline control, heptanoate (0.4 mM), or hexanoate as a negative control (0.4 mM). Treatment was initiated after 30 min of ischemia and continued through reperfusion. Myocardial CAC intermediate content was not affected by ischemia-reperfusion; however, treatment with heptanoate resulted in a more than twofold increase in fumarate and malate, with no change in citrate and succinate, while treatment with hexanoate did not increase fumarate or malate but increased succinate by 1.8-fold. There were no differences among groups in lactate exchange, glucose oxidation, oxygen consumption, and contractile power. In conclusion, despite a significant increase in the content of carbon-4 CAC intermediates, treatment with heptanoate did not result in improved mechanical function of the heart in this model of reversible ischemia-reperfusion. This suggests that reduced anaplerosis and CAC dysfunction do not play a major role in contractile and metabolic derangements observed with a 60% decrease in coronary flow followed by reperfusion.     

Myosin I and actin dynamics: the frogs weigh in

In this issue of Developmental Cell, Sokac et al. (2006) describe an intriguing new role for an actin-based motor protein in restraining actin polymerization during endocytosis in Xenopus oocytes.     

Chemical-induced, nonlethal, developmental model of dissecting aortic aneurysm

BACKGROUND: A chemical-induced, nonlethal, dissecting aortic aneurysm (DAA) is described following in utero exposure to semicarbazide, an inhibitor of the vascular enzyme semicarbazide sensitive amine oxidase (SSAO). METHODS: Sprague-Dawley rat dams were given semicarbazide (0.096-49.000 mg/kg/day) by IP injection on gestation days (GDs) 14-20, a period of rapid aortic development. Newborn rats (day 1) were killed and their thoracic organs were removed en bloc for near-serial cross sections and routine histopathology, Movat stain for elastin, and immunohistochemistry to differentiate cells involved in the evolution of the DAA. In subsequent experiments, pups from treated dams (0.096-6.125 mg/kg/day) were allowed to survive for 7 or 28 days. RESULTS: DAA occurred in nearly 100% of the rats at all doses except the lowest tested (1.530, 0.096 mg/kg/day). Dissections frequently extended to the carotids and, less frequently, to the abdominal aorta. Remodeling of vascular lesions proceeded by organization of collections of blood in vascular media (the "false lumen"), proliferation of vascular smooth muscle cells, fibrosis, and formation of irregular frayed elastic lamellae in healed vascular media. Biochemical quantitation and Western blot analysis of main extracellular matrix proteins on GD 20 showed no overt difference in expression of collagen type I, fibrillin-1, or elastin. CONCLUSION: This developmental model provides investigators an opportunity to explore the pathologic mechanisms of DAA and to examine the potential long-term effects of vascular remodeling of DAA.     

Assessment of nutritional status of gastroenterology patients in Croatia

Malnutrition is a common feature of gastroenterological diseases. In this study, nutritional status of the patients admitted to Department of Gastroenterology at University Hospital Center Zagreb was assessed. Anthropometric, dietetic, biochemical methods and method of Subjective Global Assessment (SGA) was used. The study group included 284 patients admitted to the Hospital. Malnutrition, as defined by SGA, was found in 61.1% of the patients, of whom 75% were moderately and 25% severely malnourished. Those patients classified as moderately and extremely malnourished by SGA were found to have statistically lower values of BMI, albumin, total proteins, calcium, iron, triglycerides, cholesterol, vitamin A and lymphocytes as compared to those who were adequately nourished. The prevalence of malnutrition in hospitalized patients treated at the Department of Gastroenterology is high. The use of nutritional screening with multiple measures would be important in the early identification and treatment of these patients and would help decrease this high prevalence.