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Mitochondrial fusion protein 2 (MFN2) deficiency has been shown to hinder the survival of bacteria in macrophages. Endoplasmic reticulum stress and apoptosis are vital defense mechanisms against Brucella infection, but the specific role of MFN2 in Brucella-infected macrophages remains unclear. In this study, we aimed to investigate the role of MFN2 in the infection of macrophages by Brucella abortus strain A19. The levels of CHOP and GRP78, which are molecules associated with endoplasmic reticulum stress, as well as Caspase-3 and BAX, which are pro-apoptotic molecules, were measured using confocal microscopy, qRT-PCR and Western blot in cell models infected with B. abortus A19. Additionally, the apoptosis rate of these cell models was assessed using flow cytometry. Our findings revealed a significant decrease in MFN2 levels 24 h post B. abortus A19 infection of macrophages. Interfering with MFN2 in macrophages led to an increase in Brucella-induced up-regulation of CHOP, GRP78, Caspase-3, and BAX, consequently hindering the survival of B. abortus A19 in macrophages. Conversely, infecting macrophages that overexpress MFN2 with B. abortus A19 resulted in the down-regulation of CHOP, GRP78, Caspase-3, and BAX. MFN2 mediated the downregulation of endoplasmic reticulum stress and programmed cell death in B. abortus A19-infected macrophages, thereby supported the intracellular survival of Brucella. This is the first report to highlight the key role of MFN2 in the intracellular survival of Brucella, providing a new perspective for understanding the mechanisms involved and offering a potential research direction for the development of targeted therapeutic agents against brucellosis. [ABSTRACT FROM AUTHOR]

Although synapsins are abundant synaptic vesicle proteins that are widely used as markers of presynaptic terminals, the mechanisms that target synapsins to presynaptic terminals have not been elucidated. We have addressed this question by imaging the targeting of green fluorescent protein-tagged synapsins in cultured hippocampal neurons. Whereas all synapsin isoforms targeted robustly to presynaptic terminals in wild-type neurons, synapsin Ib scarcely targeted in neurons in which all synapsins were knocked-out. Coexpression of other synapsin isoforms significantly strengthened the targeting of synapsin Ib in knock-out neurons, indicating that heterodimerization is required for synapsin Ib to target. Truncation mutagenesis revealed that synapsin la targets via distributed bin include domains B, C, and E. Although domain A was not necessary for targeting, its presence enhanced targeting. Domain D inhibited targeting, but this inhibition was overcome by domain E. Thus, multiple intermolecular and intramolecular interactions are required for synapsins to target to presynaptic terminals. [ABSTRACT FROM AUTHOR]

Tryptophan hydroxylase (TPH) is the initial and rate-limiting enzyme in serotonin biosynthesis. The enzyme activity is dependent on molecular oxygen, a tetra-hydropterin cosubstrate, and ferrous iron. The present study demonstrates that TPH is inhibited by a novel compound, p-ethynylphenylalanine (pEPA), produced by the Heck reaction of trimethylsilylacetylene with N-tertbutyloxycarbonyl- 4-iodo-L-phenylalanine methyl ester. pEPA is a more potent and specific inhibitor of TPH than p-chlorophenylalanine (pCPA). In the present study, pEPA was demonstrated to inhibit competitively and reversibly TPH in vitro (K[subi]=32.6plus or minus6.2 muM vs. tryptophan). pEPA displayed little inhibitory activity toward tyrosine hydroxylase (EC 1.14.16.2), the initial and rate-limiting enzyme for catecholamine biosynthesis, and no inhibition of phenylalanine hydroxylase or tyrosinase. In addition, pEPA was a poor ligand for the serotonin transporter and several serotonin receptors. Administration of pEPA (30 mg/kg) to rats produced a 95plus or minus5percent decrease in TPH activity in brain homogenates and a concomitant decrease in serotonin and 5-hydroxyindole-3-acetic acid levels (85percent) at 24 hours after injection. In contrast, pCPA produced a similar effect (87plus or minus5percent decrease in TPH activity) only at 10 times the concentration (300 mg/kg). These results suggest that pEPA is a selective, reversible, and potent inhibitor of TPH both in vitro and in vivo. The potential for pEPA to inhibit selectively and reversibly the biosynthesis of serotonin may contribute to the characterization of the role of serotonin in behavioral and physiological activities. [ABSTRACT FROM AUTHOR]