Large Room Temperature Magnetization Enhancement in a Copper-Based Photoactive Metal-Organic Framework.

The tris(pyridin-4-yl)amine ligand was found to exhibit a radical-actuated coloration phenomenon, and a novel copper-based color-changeable metal-organic framework (MOF) was synthesized via this photoactive ligand. After light irradiation, the photogenerated stable radicals in this framework induced increasing amplitude of magnetization (32%) at room temperature, being the largest enhancement among radical-based photochromic systems.

Cytomegalovirus retinitis in patients with AIDS before and after introduction of HAART in China.

PURPOSE: To determine the prevalence of cytomegalovirus retinitis (CMVR) and other fundus lesions in subjects with acquired immunodeficiency syndrome (AIDS) before and after the introduction of highly active antiretroviral therapy (HAART) in China. METHODS: The retrospective study included subjects with AIDS who consecutively attended a third referral center in Beijing before and after HAART was introduced. Comprehensive systemic and ophthalmic examinations, including CD4+ T-cell count, ophthalmoscopy, and fundus photography, were carried out. RESULTS: A total of 173 HIV-infected, HAART-naive individuals and 267 people undergoing HAART were included in the study. The HAART-naive group as compared with the HAART group was significantly older (39.5 ± 11.5 years versus 36.7 ± 11.2 years; p = 0.02) and included significantly more men (p = 0.045). Prevalence of CMVR, microvascular retinopathy, and optic neuropathy in the HAART group (9.0 ± 1.8%, 7.9 ± 1.7%, and 4.9 ± 1.3%, respectively) were significantly (all p≤0.001) lower than in the HAART-naive group (20.2 ± 3.1%, 31.2 ± 3.5%, and 13.9 ± 2.6%, respectively). Microvascular retinopathy was significantly associated with HAART-naive status (p<0.001; odds ratio [OR] 0.20; 95% confidence interval [CI] 0.12, 0.36) and higher age (p = 0.002; OR 1.04; 95% CI 1.10, 1.06). Cytomegalovirus retinitis was significantly associated with CD4+ cell count <50 cells/µL (p = 0.001; OR 5.50; 95% CI 1.95, 15.5), HAART-naive status (p = 0.02; OR 0.23; 95% CI 0.07, 0.79), and lower best-corrected visual acuity (p<0.001; OR 5.44; 95% CI 2.11, 14.0). CONCLUSIONS: As in Western countries, prevalence of CMVR and microvascular retinopathy in Chinese subjects with AIDS were significantly associated with a low CD4+ cell count and a HAART-naive status as the 2 major risk factors.

Reversible acetylation regulates salt-inducible kinase (SIK2) and its function in autophagy.

Salt-inducible kinase 2 (SIK2) is a serine/threonine protein kinase belonging to the AMP-activated protein kinase (AMPK) family. SIK2 has been shown to function in the insulin-signaling pathway during adipocyte differentiation and to modulate CREB-mediated gene expression in response to hormones and nutrients. However, molecular mechanisms underlying the regulation of SIK2 kinase activity remains largely elusive. Here we report a dynamic, post-translational regulation of its kinase activity that is coordinated by an acetylation-deacetylation switch, p300/CBP-mediated Lys-53 acetylation inhibits SIK2 kinase activity, whereas HDAC6-mediated deacetylation restores the activity. Interestingly, overexpression of acetylation-mimetic mutant of SIK2 (SIK2-K53Q), but not the nonacetylatable K53R variant, resulted in accumulation of autophagosomes. Further consistent with a role in autophagy, knockdown of SIK2 abrogated autophagosome and lysosome fusion. Consequently, SIK2 and its kinase activity are indispensable for the removal of TDP-43Δ inclusion bodies. Our findings uncover SIK2 as a critical determinant in autophagy progression and further suggest a mechanism in which the interplay among kinase and deacetylase activities contributes to cellular protein pool homeostasis.

Ferrophilic characteristics of Vibrio vulnificus and potential usefulness of iron chelation therapy.

We determined the ferrophilic characteristics of Vibrio vulnificus to evaluate the potential usefulness of iron chelation therapy for the prevention of V. vulnificus infection. Readily available non-transferrin-bound iron (NTBI) is required for the initiation of V. vulnificus growth under in vitro iron-limited conditions and human ex vivo conditions. NTBI aided efficient transferrin-bound iron (TBI) use by V. vulnificus, and the vulnibactin-mediated iron-uptake system was expressed after bacterial growth had been started by NTBI. V. vulnificus required higher NTBI levels for the initiation of growth, produced siderophores at lower levels, and used TBI less efficiently than other bacteria. In addition, the growth of V. vulnificus was inhibited by deferiprone, a clinically available iron chelator. These results show that V. vulnificus is a ferrophilic bacterium that requires higher NTBI levels than other pathogens and that iron chelation therapy might be an effective means of preventing the in vivo growth of V. vulnificus in susceptible patients.

Vibrio vulnificus metalloprotease VvpE has no direct effect on iron-uptake from human hemoglobin.

This study was designed to determine whether or not Vibrio vulnificus metalloprotease VvpE can promote iron uptake via the proteolytic cleavage of human hemoglobin. We found that V. vulnificus utilized hemoglobin as an iron source more efficiently via the vulnibactin-mediated iron-uptake system than via the HupA-mediated iron-uptake system and, of the proteases produced by V. vulnificus, VvpE was found to be the only protease capable of destroying hemoglobin. However, VvpE expression, on both the transcriptional and protein levels, was suppressed in iron-limited media. However, vvpE transcription, but not extracellular VvpE production, was reactivated by the addition of hemoglobin or inorganic iron into iron-limited media. Moreover, vvpE transcription began only in the late growth phase when V. vulnificus had already consumed most of the iron for growth. In addition, neither vvpE mutation nor in trans vvpE complementation affected the ability of V. vulnificus to acquire iron or to grow in iron-limited media or in cirrhotic ascites containing hemoglobin. Hemoglobin added into iron-limited media was not destroyed, but gradually formed an insoluble aggregate during culture; this aggregation of hemoglobin occurred regardless of vvpE mutation or complementation. These results indicate that VvpE is not required for efficient iron uptake from hemoglobin. On the contrary, hemoglobin or iron is required for efficient vvpE transcription. In addition, a discrepancy exists between vvpE transcription and extracellular VvpE production in iron-limited media containing inorganic iron or hemoglobin, which suggests that additional unknown posttranscriptional events may be involved in the extracellular production of VvpE.

Suppression and inactivation of Vibrio vulnificus hemolysin in cirrhotic ascites, a human ex vivo experimental system.

To elucidate the mechanisms underlying the in vivo suppression and inactivation of Vibrio vulnificus hemolysin (VvhA), we used cirrhotic ascites fluid as a human ex vivo experimental system. VvhA expression was suppressed in proportion to the amount of cirrhotic ascites. The expression of vvhA in undiluted cirrhotic ascites could be suppressed further by the addition of glucose, a constituent of cirrhotic ascites. VvhA was readily inactivated in the presence of cirrhotic ascites by a cholesterol-mediated oligomerization and interaction with an undefined constituent(s) of cirrhotic ascites. These results indicate that the expression of vvhA can be suppressed and that any VvhA produced is inactivated by the constituents of cirrhotic ascites. Our results suggest that only a very small portion of the VvhA that is produced in human body fluids may actually contribute to the pathogenesis of V. vulnificus septicemia. It is suggested that cirrhotic ascites could be used as a human ex vivo experimental system for the studies on the in vivo expression and the significance of V. vulnificus virulence factors.

Swarming differentiation of vibrio vulnificus downregulates the expression of the vvhBA hemolysin gene via the LuxS quorum-sensing system.

Swarming has proven to be a good in vitro model for bacterial surface adherence and colonization, and the swarming differentiation of a bacterium has been shown to be coupled with changes in the expression of virulence factors associated with its invasiveness, particularly in the early stages of infection. In this study, we attempted to determine whether the expression of vvhA, which encodes for hemolysin/cytolysin (VvhA), is either upregulated or downregulated during the swarming differentiation of V. vulnificus. The insertional inactivation of vvhA itself exerted no detectable effect on the expression of V. vulnificus swarming motility. However, in our lacZ-fused vvhA transcriptional reporter assay, vvhA expression decreased in swarming V. vulnificus as compared to non-swarming or planktonic V. vulnificus. The reduced expression of vvhA in swarming V. vulnificus increased as a result of the deletional inactivation of luxS, a gene associated with quorum sensing. These results show that vvhA expression in swarming V. vulnificus is downregulated via the activity of the LuxS quorum-sensing system, suggesting that VvhA performs no essential role in the invasiveness of V. vulnificus via the adherence to and colonization on the body surfaces required in the early stages of the infection. However, VvhA may play a significant role in the pathophysiological deterioration occurring after swarming V. vulnificus is differentiated into planktonic V. vulnificus.

Vibrio vulnificus vulnibactin, but not metalloprotease VvpE, is essentially required for iron-uptake from human holotransferrin.

The roles of metalloprotease (VvpE) and catechol-siderophore (vulnibactin) in the uptake of iron from human transferrins by Vibrio vulnificus have been determined using different experimental conditions and methods. Therefore, in this study, we attempted to elucidate the roles of VvpE and vulnibactin using the same methods and experimental conditions, in an in vitro and a human ex vivo system, and in accordance with the molecular version of Koch's postulates. Neither vvpE mutation nor in trans vvpE complementation affected vulnibactin production, iron-assimilation from human holotransferrin (HT), and bacterial growth in a HT-containing deferrated Heart-Infusion medium (HT-DF-HI) or a HT-containing cirrhotic ascites (HT-CA). In contrast, the mutation of fur gene encoding Fur, a repressor regulating expression of the vulnibactin-mediated iron-uptake system, derepressed vulnibactin production, and facilitated iron-assimilation from HT and bacterial growth in HT-DF-HI or HT-CA. The mutation of vis gene encoding isochorismate synthase required for vulnibactin synthesis abolished vulnibactin production, iron-assimilation from HT and bacterial growth in HT-DF-HI or HT-CA. These results demonstrate that vulnibactin is essentially required for iron-assimilation from transferrin, and that VvpE has no direct effect on facilitating vulnibactin-mediated iron-assimilation from transferrin in vitro or in a human ex vivo system.

Proteases of a Bacillus subtilis clinical isolate facilitate swarming and siderophore-mediated iron uptake via proteolytic cleavage of transferrin.

We isolated a highly serine protease-producing Bacillus subtilis strain (PRY) from a clinical sample and identified it through biochemical testing and ribosomal DNA sequencing. The PRY strain exhibited a robust swarming behavior and was able to digest human transferrin efficiently, concomitantly with the production of catechol-siderophore in the exponential growth phase. The growth of PRY was in proportion to increased iron availability resulting from transferrin destruction. These results suggest that proteases of the B. subtilis PRY strain may play a significant role in the pathogenesis of human infections by facilitating siderophore-mediated iron uptake from transferrin and swarming motility.

Effect of the crp mutation on the utilization of transferrin-bound iron by Vibrio vulnificus.

Cyclic AMP-cAMP receptor protein (CRP) complex plays an essential role in the global regulation of Vibrio vulnificus virulence. We found that growth retardation of V. vulnificus caused by mutation of the crp gene encoding CRP was exacerbated under iron-limited conditions. Accordingly, we investigated the effect of crp mutation on the expression of the vulnibactin-mediated iron-uptake system and the ability of V. vulnificus to utilize transferrin-bound iron, and thus to grow in cirrhotic ascites, a human ex vivo system. The production of vulnibactin was suppressed, and the transcription of the vis and vuuA genes, which encode an enzyme required for vulnibactin synthesis and vulnibactin receptor protein, was also suppressed in the crp mutant. Moreover, the crp mutant could not utilize transferrin-bound iron, and its growth was severely suppressed both on transferrin-bound iron and in cirrhotic ascites. All the defects in the crp mutant were recovered by the in trans complementation of the wild-type crp gene. Putative CRP-binding sequences were found in the regulatory regions of the fur, vis and vuuA genes. These results indicate that crp mutation attenuates the ability to grow on transferrin-bound iron and in a human body fluid by down-regulating the vulnibactin-mediated iron-uptake system.

Human serum albumin enhances the hemolytic activity of Vibrio vulnificus.

Vibrio vulnificus hemolysin (VvhA) is inactivated in the late growth phase by its oligomerization. Albumin is known to affect the activities of many bacterial toxins. In this study, we investigated the effects of human or bovine serum albumin (HSA or BSA) on the production and activity of VvhA. HSA did not affect V. vulnificus growth and vvhA transcription. However, VvhA hemolytic activity in culture supernatants was significantly higher in the presence of HSA than in the absence of HSA. By Western blot analysis, the oligomerization of VvhA was inhibited and the remaining active VvhA monomer was increased in culture supernatants containing HSA. BSA produced similar results. These findings indicate that both HSA and BSA stabilize VvhA and delay VvhA inactivation by oligomerization, and thus enhance VvhA activity.

Inactivation of Vibrio vulnificus hemolysin by oligomerization but not proteolysis.

Vibrio vulnificus extracellular protease (VvpE) is believed to destroy its hemolysin (VvhA) in the late growth phase, without obvious experimental evidence. So, we attempted to elucidate the mechanism. The hemolytic activity steeply increased with the expression of the VvhA in the early growth phase, and then abruptly declined with the expression of VvpE in the late growth phase. However, the VvhA activity also abruptly declined in a VvpE-deficient mutant. In Western blot, the degradation of VvhA was not observed; instead, the oligomerization of VvhA increased with the concomitant loss of hemolytic activity. These results evidently indicate that the inactivation of VvhA is due to the novel oligomerization of VvhA by unknown mechanism, but not to the destruction of VvhA by VvpE, so that the routine functional assay measuring hemolytic activity cannot reflect the actual production of VvhA.

Production of catechol-siderophore and utilization of transferrin-bound iron in Bacillus cereus.

In the present study we attempted to ascertain whether Bacillus cereus was able to produce catechol-siderophore(s), and whether it was able to utilize transferrin-bound iron. The growth of B. cereus was stimulated in proportion to the iron-saturation level of the transferrin, and catechol-siderophores were produced in inverse proportion to this level. B. cereus was proved to uptake iron from partially iron-saturated transferrin or holotransferrin, without destroying the transferrin by its proteases. The catechol-siderophores from B. cereus were able to sustain and augment its growth on the transferrin-bound iron. These results indicate that B. cereus has the ability to produce catechol-siderophores, and to utilize transferrin-bound iron as an iron source for growth, via the siderophore-mediated iron-uptake system.

Vibrio vulnificus metalloprotease VvpE has no direct effect on the iron-assimilation from human holotransferrin.

In order to elucidate the role of Vibrio vulnificus metalloprotease VvpE in the uptake of iron from human transferrin, we constructed a VvpE-deficient mutant and a merozygotic vvpE-transcriptional reporter from the wild type strain MO6-24/O. All three strains were able to grow only in deferrated Heart Infusion broth (DF-HI) with human holotransferrin (HT), but not in DF-HI containing partially iron-saturated transferrin or apotransferrin, without noticeable differences among the strains. All strains consumed most iron in the early growth phase. Both the transcription and extracellular production of VvpE proceeded at undetectable levels when bacterial growth was severely retarded in the DF-HI. When HT or FeCl(3) was added to the DF-HI, the retarded bacterial growth was restored and vvpE transcription dramatically increased in the late growth phase, but the extracellular VvpE production was negligible as compared to its transcription. All strains were unable to degrade HT even in normal HI broth containing HT, in which extracellular VvpE activity was remarkably high. The uptake of iron from HT in all strains was consistent with the production of catechol-siderophore rather than hydroxamate-siderophore. Similar results were also observed when clinical isolates from septicemic patients were used. In conclusion, we determined that VvpE was not directly involved in the siderophore-mediated iron-uptake from human transferrin. In addition, the discrepancy between the transcription and extracellular production of VvpE suggests that additional posttranscriptional events are involved in the extracellular production of VvpE.

Staphylococcus aureus siderophore-mediated iron-acquisition system plays a dominant and essential role in the utilization of transferrin-bound iron.

Staphylococcus aureus is known to be capable of utilizing transferrin-bound iron, via both siderophore- and transferrin-binding protein (named IsdA)-mediated iron-acquisition systems. This study was designed in order to determine which iron-acquisition system plays the essential or dominant role with respect to the acquisition of iron from human transferrin, in the growth of S. aureus. Holotransferrin (HT) and partially iron-saturated transferrin (PT), but not apotransferrin (AT), were found to stimulate the growth of S. aureus. S. aureus consumed most of the transferrin-bound iron during the exponential growth phase. Extracellular proteases were not, however, involved in the liberation of iron from transferrin. Transferrin-binding to the washed whole cells via IsdA was not observed during the culture. The expression of IsdA was observed only in the deferrated media with AT, but not in the media supplemented with PT or HT. In contrast, siderophores were definitely produced in the deferrated media with PT and HT, as well as in the media supplemented with AT. The siderophores proved to have the ability to remove iron directly from transferrin, but the washed whole cells expressing IsdA did not. In the bioassay, the growth of S. aureus on transferrin-bound iron was stimulated by the siderophores alone. These results demonstrate that the siderophore-mediated iron-acquisition system plays a dominant and essential role in the uptake of iron from transferrin, whereas the IsdA-mediated iron-acquisition system may play only an ancillary role in the uptake of iron from transferrin.

Growth of Staphylococcus aureus with defective siderophore production in human peritoneal dialysate solution.

In this study, we attempted to determine the effects of iron-availability and the activity of the bacterial iron-uptake system (IUS) on the growth of Staphylococcus aureus in human peritoneal dialysate (HPD) solution. A streptonigrin-resistant S. aureus (SRSA) strain, isolated from S. aureus ATCC 6538, exhibited defective siderophore production, thereby resulting in ineffective uptake of iron from low iron-saturated transferrin. The growth of both strains was stimulated in HPD solution supplemented with FeCl3 and holotransferrin, but growth was inhibited in HPD solution which had been supplemented with apotransferrin and dipyridyl. The SRSA strain grew less robustly than did its parental strain in both iron-supplemented HPD solution and regular HPD solution. These results indicate that iron-availability and siderophore-mediated IUS activity in particular, the ability to produce siderophores and thus capture iron from low iron-saturated transferrin play critical roles in the growth of S. aureus in HPD solution. Our results also indicated that the possibility of using iron chelators as therapeutic or preventive agents warrants further evaluation.

Bacterial growth in amniotic fluid is dependent on the iron-availability and the activity of bacterial iron-uptake system.

In the present study, the relationship among iron-availability, antibacterial activity, role of meconium as an iron source and the activity of bacterial iron-uptake system (IUS) for bacterial growth in amniotic fluid (AF) were investigated. Staphylococcus aureus ATCC 6538 and its streptonigrin-resistant (SR) mutant with defective IUS were used as the test strains. The growth of S. aureus in AF was stimulated dose-dependently by addition of meconium. Bacterial growth stimulated by meconium was re-inhibited dose-dependently by addition of iron-chelator, dipyridyl and apotransferrin. Iron concentration was correlated with the meconium content in AF (r(2)= 0.989, p=0.001). High-affinity IUS of S. aureus was expressed only in AF but not in AF with meconium. The growth of SR strain was more retarded than that of the parental strain in the iron-deficient brain heart infusion (ID-BHI), clear AF and AF containing apotransferrin. The retarded growth of both strains in the ID-BHI and AF was recovered by addition of holotransferrin, hemoglobin and FeCl3. Taken together, the antibacterial activity of AF is closely related with low iron-availability. Bacterial growth in AF considerably depends on the activity of bacterial IUS. Meconium acts as one of the exogenous iron-sources and thus can stimulate bacterial growth in AF.