Protein Tpr is required for establishing nuclear pore-associated zones of heterochromatin exclusion

Amassments of heterochromatin in somatic cells occur in close contact with the nuclear envelope (NE) but are gapped by channel- and cone-like zones that appear largely free of heterochromatin and associated with the nuclear pore complexes (NPCs). To identify proteins involved in forming such heterochromatin exclusion zones (HEZs), we used a cell culture model in which chromatin condensation induced by poliovirus (PV) infection revealed HEZs resembling those in normal tissue cells. HEZ occurrence depended on the NPC-associated protein Tpr and its large coiled coil-forming domain. RNAi-mediated loss of Tpr allowed condensing chromatin to occur all along the NE's nuclear surface, resulting in HEZs no longer being established and NPCs covered by heterochromatin. These results assign a central function to Tpr as a determinant of perinuclear organization, with a direct role in forming a morphologically distinct nuclear sub-compartment and delimiting heterochromatin distribution

Improved Learning and Memory in Aged Mice Deficient in Amyloid β-Degrading Neutral Endopeptidase

BACKGROUND: Neutral endopeptidase, also known as neprilysin and abbreviated NEP, is considered to be one of the key enzymes in initial human amyloid-beta (Abeta) degradation. The aim of our study was to explore the impact of NEP deficiency on the initial development of dementia-like symptoms in mice. METHODOLOGY/PRINCIPAL FINDINGS: We found that while endogenous Abeta concentrations were elevated in the brains of NEP-knockout mice at all investigated age groups, immunohistochemical analysis using monoclonal antibodies did not detect any Abeta deposits even in old NEP knockout mice. Surprisingly, tests of learning and memory revealed that the ability to learn was not reduced in old NEP-deficient mice but instead had significantly improved, and sustained learning and memory in the aged mice was congruent with improved long-term potentiation (LTP) in brain slices of the hippocampus and lateral amygdala. Our data suggests a beneficial effect of pharmacological inhibition of cerebral NEP on learning and memory in mice due to the accumulation of peptides other than Abeta degradable by NEP. By conducting degradation studies and peptide measurements in the brain of both genotypes, we identified two neuropeptide candidates, glucagon-like peptide 1 and galanin, as first potential candidates to be involved in the improved learning in aged NEP-deficient mice. CONCLUSIONS/SIGNIFICANCE: Thus, the existence of peptides targeted by NEP that improve learning and memory in older individuals may represent a promising avenue for the treatment of neurodegenerative diseases

Genetic Deficiency in Neprilysin or Its Pharmacological Inhibition Initiate Excessive Stress-Induced Alcohol Consumption in Mice

Both acquired and inherited genetic factors contribute to excessive alcohol consumption and the corresponding development of addiction. Here we show that the genetic deficiency in neprilysin [NEP] did not change the kinetics of alcohol degradation but led to an increase in alcohol intake in mice in a 2-bottle-free-choice paradigm after one single stress stimulus (intruder). A repetition of such stress led to an irreversible elevated alcohol consumption. This phenomenon could be also observed in wild-type mice receiving an orally active NEP inhibitor. We therefore elucidated the stress behavior in NEP-deficient mice. In an Elevated Plus Maze, NEP knockouts crossed more often the area between the arms, implicating a significant stronger stress response. Furthermore, such animals showed a decreased locomotor activity under intense light in a locomotor activity test, identifying such mice to be more responsive in aversive situations than their wild-type controls. Since the reduction in NEP activity itself does not lead to significant signs of an altered alcohol preference in mice but requires an environmental stimulus, our findings build a bridge between stress components and genetic factors in the development of alcoholism. Therefore, targeting NEP activity might be a very attractive approach for the treatment of alcohol abuse in a society with increasing social and financial stress

Influence of pharmacological inhibition of NEP activity on the alcohol-preference ratio.

<p>(<b>A</b>) Effects of candoxatril (200 mg/kg/day) on central and peripheral NEP activity; (<b>B</b>) Candoxatril-induced differences in the alcohol preference ratio and (<b>C</b>) total fluid intake. All data sets include at least measurements at 8 independent successive time points. **<i>P</i><0.01, ***<i>P</i><0.001 vs. control.</p

Influence of NEP activity on the alcohol-preference ratio in transgenic mice.

<p>(<b>A</b>) No significant differences between NEP-deficient (hatched bars) and NEP wild-type mice (white bars) in absolute alcohol consumption (left panel), total fluid consumption (second left panel), alcohol/total fluid ratio (second right panel), and in alcohol degradation (measured 2 h after alcohol i.p. injection; right panel) under stress-free conditions; (<b>B</b>) Development of stress-induced differences in the preference ratio between the both genotypes; (<b>C</b>) Development of stress-induced differences in the preference ratio between the both genotypes between days 22 and 70 of the experiment; (<b>D</b>) No fading of stress-induced differences after second stress phase in the preference ratio of NEP-deficient and NEP wild-type mice at 3 consecutive periods of approx 30 days. All data sets include at least measurements at 8 independent successive time points. **<i>P</i><0.01, ***<i>P</i><0.001 vs. wild-type.</p

Response of mice with NEP deficiency in two independent tests of emotional behavior.

<p>NEP deficient mice (hatched bars) did not show alterations in the time spent in the (<b>A</b>) closed arm and (<b>B</b>) in the time travelling, (<b>C</b>) but number of transitions between the chambers crossed the area between the arms significantly more frequent. (<b>D</b>) Using a motility monitor system, NEP-deficient mice did show significant reduction in travelling time, (<b>E</b>) distance travelled, and (<b>F</b>) time in the middle (open field) of the monitor system. All data sets include at least measurements at 8 independent successive time points. *<i>P</i><0.05, **<i>P</i><0.01 vs. control.</p