Enterococcus faecalis is a bacterium that normally inhabits the gastrointestinal tracts of humans and other animals. Although these bacteria are members of our native gut flora, they can cause life-threatening infections in hospitalized patients. Antibiotic resistance genes appear to be readily shared among high-risk E. faecalis strains, and multidrug resistance in these bacteria limits treatment options for infections. Here, we find that CRISPR-Cas and restriction-modification systems, which function as adaptive and innate immune systems in bacteria, significantly impact the spread of antibiotic resistance genes in E. faecalis populations. The loss of these systems in high-risk E. faecalis suggests that they are immunocompromised, a tradeoff that allows them to readily acquire new genes and adapt to new antibiotics.

Background:The role of HDAC1 in the regulation of neuronal survival is unresolved. Results: In cooperation with HDRP, HDAC1 promotes neuronal survival, but when it interacts with HDAC3, HDAC1 promotes neuronal death. Conclusion: HDAC1 can protect neurons or promote neuronal death depending on whether it interacts with HDRP or HDAC3. Significance: Our results provide insight into the role of HDAC1 in the regulation of neuronal survival.

The methyl-CpG Binding Protein 2 (MeCP2) is a widely expressed protein, mutations of which cause Rett syndrome. The level of MeCP2 is highest in the brain where it is expressed selectively in mature neurons. Its functions in postmitotic neurons are not known. The MeCP2 gene is alternatively-spliced to generate two proteins with different N-termini, designated as MeCP2-e1 and MeCP2-e2. The physiological significance of these two isoforms has not been elucidated and it is generally assumed they are functionally equivalent. We report that in cultured cerebellar granule neurons induced to die by low potassium treatment and in Aβ-treated cortical neurons, Mecp2-e2 expression is upregulated whereas expression of the Mecp2-e1 isoform is downregulated. Knockdown of Mecp2-e2 protects neurons from death whereas knockdown of the e1 isoform has no effect. Forced expression of MeCP2-e2, but not MeCP2-e1, promotes apoptosis in otherwise healthy neurons. We find that MeCP2-e2 interacts with the forkhead protein FoxG1, mutations of which also cause Rett syndrome. FoxG1 has been shown to promote neuronal survival and its downregulation leads to neuronal death. We find that elevated FoxG1 expression inhibits MeCP2-e2 neurotoxicity. MeCP2-e2 neurotoxicity is also inhibited by IGF-1, which prevents the neuronal death-associated downregulation of FoxG1 expression, and by Akt, activation of which is necessary for FoxG1-mediated neuroprotection. Finally, MeCP2-e2 neurotoxicity is enhanced if FoxG1 expression is suppressed or in neurons cultured from FoxG1-haplodeficient mice. Our results indicate that Mecp2-e2 promotes neuronal death and that this activity is normally inhibited by FoxG1. Reduced FoxG1expression frees Mecp2-e2 to promote neuronal death.

Neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Huntington's disease and conditions such as ischemic stroke affect millions of individuals annually and exert an enormous financial burden on society. A hallmark of these conditions is the abnormal loss of neurons. Currently, there are no effective strategies to prevent neuronal death in these pathologies. We report that several 2-arylidine and 2-hetarylidin derivatives of the 1,4-benzoxazines class of compounds are highly protective in tissue culture models of neurodegeneration. Results obtained using pharmcalogical inhibitors indicate that neuroprotection by these compounds does not involve the Raf-MEK-ERK or PI-3 kinase-Akt signaling pathways nor other survival-promoting molecules such as protein kinase A (PKA), calcium calmodulin kinase A (CaMK), and histone deacetylases (HDACs). We tested one of these compounds, (Z)-6-amino-2-(3',5'-dibromo-4'-hydroxybenzylidene)-2H-benzo[b][1,4]oxazin-3(4H)-one, designated as HSB-13, in the 3-nitropropionic acid (3-NP)-induced mouse model of Huntington's disease. HSB-13 reduced striatal degeneration and improved behavioral performance in mice administered with 3-NP. Furthermore, HSB-13 was protective in a Drosophila model of amyloid precursor protein (APP) toxicity. To understand how HSB-13 and other 1,4-benzoxazines protect neurons, we performed kinase profiling analyses. These analyses showed that HSB-13 inhibits GSK3, p38 MAPK, and cyclin-dependent kinases (CDKs). In comparison, another compound, called ASK-2a, that protects cerebellar granule neurons against low-potassium-induced death inhibits GSK3 and p38 MAPK but not CDKs. Despite its structural similarity to HSB-13, however, ASK-2a is incapable of protecting cortical neurons and HT22 cells against homocysteic acid (HCA)-induced or Abeta toxicity, suggesting that protection against HCA and Abeta depends on CDK inhibition. Compounds described in this study represent a novel therapeutic tool in the treatment of neurodegenerative diseases.

CRISPR-Cas systems are barriers to horizontal gene transfer (HGT) in bacteria. Little is known about CRISPR-Cas interactions with conjugative plasmids, and studies investigating CRISPR-Cas/plasmid interactions in in vivo models relevant to infectious disease are lacking. These are significant gaps in knowledge because conjugative plasmids disseminate antibiotic resistance genes among pathogens in vivo, and it is essential to identify strategies to reduce the spread of these elements. We use enterococci as models to understand the interactions of CRISPR-Cas with conjugative plasmids. Enterococcus faecalis is a native colonizer of the mammalian intestine and harbors pheromone-responsive plasmids (PRPs). PRPs mediate inter- and intraspecies transfer of antibiotic resistance genes. We assessed E. faecalis CRISPR-Cas anti-PRP activity in the mouse intestine and under different in vitro conditions. We observed striking differences in CRISPR-Cas efficiency in vitro versus in vivo. With few exceptions, CRISPR-Cas blocked intestinal PRP dissemination, while in vitro, the PRP frequently escaped CRISPR-Cas defense. Our results further the understanding of CRISPR-Cas biology by demonstrating that standard in vitro experiments do not adequately model the in vivo antiplasmid activity of CRISPR-Cas. Additionally, our work identifies several variables that impact the apparent in vitro antiplasmid activity of CRISPR-Cas, including planktonic versus biofilm settings, different donor-to-recipient ratios, production of a plasmid-encoded bacteriocin, and the time point at which matings are sampled. Our results are clinically significant because they demonstrate that barriers to HGT encoded by normal (healthy) human microbiota can have significant impacts on in vivo antibiotic resistance dissemination. IMPORTANCE CRISPR-Cas is a type of immune system in bacteria that is hypothesized to be a natural impediment to the spread of antibiotic resistance genes. In this study, we directly assessed the impact of CRISPR-Cas on antibiotic resistance dissemination in the mammalian intestine and under different in vitro conditions. We observed a robust effect of CRISPR-Cas on in vivo but not in vitro dissemination of antibiotic resistance plasmids in the native mammalian intestinal colonizer Enterococcus faecalis. We conclude that standard in vitro experiments currently do not appropriately model the in vivo conditions where antibiotic resistance dissemination occurs between E. faecalis strains in the intestine. Moreover, our results demonstrate that CRISPR-Cas present in native members of the mammalian intestinal microbiota can block the spread of antibiotic resistance plasmids.