Sleeping Beauty mRNA-LNP enables stable rAAV transgene expression in mouse and NHP hepatocytes and improves vector potency.

Recombinant adeno-associated virus (rAAV) vector gene delivery systems have demonstrated great promise in clinical trials but continue to face durability and dose-related challenges. Unlike rAAV gene therapy, integrating gene addition approaches can provide curative expression in mitotically active cells and pediatric populations. We explored a novel in vivo delivery approach based on an engineered transposase, Sleeping Beauty (SB100X), delivered as an mRNA within a lipid nanoparticle (LNP), in combination with an rAAV-delivered transposable transgene. This combinatorial approach achieved correction of ornithine transcarbamylase deficiency in the neonatal Spfash mouse model following a single delivery to dividing hepatocytes in the newborn liver. Correction remained stable into adulthood, while a conventional rAAV approach resulted in a return to the disease state. In non-human primates, integration by transposition, mediated by this technology, improved gene expression 10-fold over conventional rAAV-mediated gene transfer while requiring 5-fold less vector. Additionally, integration site analysis confirmed a random profile while specifically targeting TA dinucleotides across the genome. Together, these findings demonstrate that transposable elements can improve rAAV-delivered therapies by lowering the vector dose requirement and associated toxicity while expanding target cell types.

Systemic neutrophils are triggered by respiratory Bacillus Calmette- Guérin and mediate pulmonary mycobacterial clearance in synergy with the triggering receptor expressed on myeloid cells 1.

Tuberculosis remains a threat to public health. The only approved vaccine, Bacillus Calmette-Guérin (BCG), is administered intradermally and provides limited protection, and its effect on innate immunity via the respiratory route has not been fully elucidated. A mouse model with genetically depleted TREM1 and seven-color flow cytometry staining were used to characterize the comprehensive immune response induced by respiratory BCG, through evaluating organ bacterial loads, lung histopathology, and lung immunohistochemistry. During respiratory BCG infection, the murine lungs displayed effective bacterial clearance. Notably, marked differences in neutrophils were observed between thymus and bone marrow cells, characterized by a significant increase in the expression of the triggering receptor expressed on myeloid cells 1 (TREM1). Subsequently, upon depletion of TREM1, a reduction in pulmonary neutrophils was observed, which further exacerbated bacterial loads and resulted in worsened pathology following respiratory BCG infection. In summary, up-regulated expression of TREM1 in rapidly increasing circulating neutrophil by pulmonary BCG is required for an efficient host response to BCG infection, and suggests the important role of TREM1 in neutrophil-related pulmonary bacteria clearance and pathology.

Therapeutic effect of fastigial nucleus stimulation is mediated by the microRNA-182 & microRNA-382/BDNF signaling pathways in the treatment of post-stroke depression.

The deregulation of Brain-Derived Neurotrophic Factor (BDNF) was reported to be responsible for the development of post-stroke depression (PSD), while the stimulation of the fastigial nucleus (FN) can be used to treat PDS by down-regulating the expression of miR-182 and miR-382. Therefore, we aim to test the hypothesis that the therapeutic effect of FN stimulation obtained in the treatment of PSD is mediated by the miR-382&miR-182/BDNF mRNA signaling pathways. Rat models of PSD were established and divided into sham, stroke, PSD and PSD + FNS groups to receive different treatments. Post-stroke depression-like behaviors were observed after the initiation of the treatments. TUNEL assay, Western Blot, IHC assay, real-time PCR, bioinformatics tools and luciferase assays were performed to examine the effect of FN stimulation on the expression of miR-182, miR-382 and BDNF mRNA/protein, as well as to further clarify the role of miR-382&miR-182/BDNF mRNA signaling pathways in FN stimulation. Post-stroke depression-like behaviors were significantly reduced in PSD rats. In contrary, the treatment by FN stimulation alleviated the symptoms of PSD and reduced the apoptosis index in the PSD group. Furthermore, in the PSD group, BDNF mRNA/protein levels were suppressed while the miR-382/miR-182 levels were both significantly up-regulated. After the treatment of FN stimulation, BDNF mRNA/protein levels were partly recovered, while miR-382/miR-182 levels was decreased. Furthermore, BDNF was identified as a virtual target of miR-382 and miR-182. In conclusion, FN stimulation increases the expression of BDNF via down-regulating the expression of miR-382/miR-182, thus exhibiting a positive effect in the management of PSD.

The lip gene contributes to the virulence of Aeromonas veronii strain TH0426.

Aeromonas veronii (A. veronii) is a pathogen that can infect aquatic organisms and mammals and has caused irrecoverable economic losses to the aquaculture industry. The results of an epidemiological investigation showed that the number of cases of A. veronii have increased gradually in recent years, and its drug resistance and virulence has shown an upward trend. In this study, we constructed an A. veronii mutant strain Δlip, by homologous recombination and studied its function. The results showed that there was no significant difference in the biofilm formation ability between the Δlip and the wild-type strain, but the toxicity of the Δlip to EPC cells and its ability to adhere to EPC cells were significantly reduced. The LD50 value of the Δlip to zebrafish was 7.40-fold higher than that of the wild-type strain. In addition, after 24 h and 72 h, the bacterial loads of the Δlip in the organs of crucian carp were significantly lower than those in the wild-type strain. In conclusion, the mutant strain Δlip led to a decrease in the adhesion and virulence of the wild-type strain, which lays a foundation to further understand lip gene function and the pathogenic mechanism of A. veronii.

Novel mRNA-Based Therapy Reduces Toxic Galactose Metabolites and Overcomes Galactose Sensitivity in a Mouse Model of Classic Galactosemia.

Classic galactosemia (CG) is a potentially lethal inborn error of galactose metabolism that results from deleterious mutations in the human galactose-1 phosphate uridylyltransferase (GALT) gene. Previously, we constructed a GalT-/- (GalT-deficient) mouse model that exhibits galactose sensitivity in the newborn mutant pups, reduced fertility in adult females, impaired motor functions, and growth restriction in both sexes. In this study, we tested whether restoration of hepatic GALT activity alone could decrease galactose-1 phosphate (gal-1P) and plasma galactose in the mouse model. The administration of different doses of mouse GalT (mGalT) mRNA resulted in a dose-dependent increase in mGalT protein expression and enzyme activity in the liver of GalT-deficient mice. Single intravenous (i.v.) dose of human GALT (hGALT) mRNA decreased gal-1P in mutant mouse liver and red blood cells (RBCs) within 24 h with low levels maintained for over a week. Repeated i.v. injections increased hepatic GalT expression, nearly normalized gal-1P levels in liver, and decreased gal-1P levels in RBCs and peripheral tissues throughout all doses. Moreover, repeated dosing reduced plasma galactose by 60% or more throughout all four doses. Additionally, a single intraperitoneal dose of hGALT mRNA overcame the galactose sensitivity and promoted the growth in a GalT-/- newborn pup.

Convenient Agarose Preparation with Hydrogen Peroxide and Desulfation Process Analysis.

Agarose is a natural seaweed polysaccharide and widely used in the medicine, food, and biological fields because of its high gel strength, non-toxicity, and electrical neutrality. The sulfate group is one of the main charged groups that affect the performance of agarose. In the present study, a simple, eco-friendly, and efficient method was explored for agarose preparation. After desulfation with hydrogen peroxide (H2O2), the sulfate content of agar reached 0.21%. Together with gel strength, electroendosmosis, gelling and melting temperature, the indicators of desulfated agar met the standards of commercially available agarose. Notably, the desulfated agar can be used as an agarose gel electrophoresis medium to separate DNA molecules, and the separation effect is as good as that of commercially available agarose. Further, the H2O2 desulfation process was analyzed. The addition of a hydroxyl radical (HO•) scavenger remarkably decreased the H2O2 desulfation rate, indicating that HO• has a certain role in agar desulfation. Sulfate content detection indicated that sulfur was removed from agar molecules in the form of sulfate ions (SO42-) and metal sulfate. The band absence at 850 cm-1 indicated that the sulfate groups at C-4 of D-galactose in sulfated galactan were eliminated.

mRNA Therapy Improves Metabolic and Behavioral Abnormalities in a Murine Model of Citrin Deficiency.

Citrin deficiency is an autosomal recessive disorder caused by loss-of-function mutations in SLC25A13, encoding the liver-specific mitochondrial aspartate/glutamate transporter. It has a broad spectrum of clinical phenotypes, including life-threatening neurological complications. Conventional protein replacement therapy is not an option for these patients because of drug delivery hurdles, and current gene therapy approaches (e.g., AAV) have been hampered by immunogenicity and genotoxicity. Although dietary approaches have shown some benefits in managing citrin deficiency, the only curative treatment option for these patients is liver transplantation, which is high-risk and associated with long-term complications because of chronic immunosuppression. To develop a new class of therapy for citrin deficiency, codon-optimized mRNA encoding human citrin (hCitrin) was encapsulated in lipid nanoparticles (LNPs). We demonstrate the efficacy of hCitrin-mRNA-LNP therapy in cultured human cells and in a murine model of citrin deficiency that resembles the human condition. Of note, intravenous (i.v.) administration of the hCitrin-mRNA resulted in a significant reduction in (1) hepatic citrulline and blood ammonia levels following oral sucrose challenge and (2) sucrose aversion, hallmarks of hCitrin deficiency. In conclusion, mRNA-LNP therapy could have a significant therapeutic effect on the treatment of citrin deficiency and other mitochondrial enzymopathies with limited treatment options.

Sucrose nonfermenting AMPK-related kinase (SNARK) regulates exercise-stimulated and ischemia-stimulated glucose transport in the heart.

The signaling mechanisms mediating myocardial glucose transport are not fully understood. Sucrose nonfermenting AMP-activated protein kinase (AMPK)-related kinase (SNARK) is an AMPK-related protein kinase that is expressed in the heart and has been implicated in contraction-stimulated glucose transport in mouse skeletal muscle. We first determined if SNARK is phosphorylated on Thr208 , a site critical for SNARK activity. Mice were treated with exercise, ischemia, submaximal insulin, or maximal insulin. Treadmill exercise slightly, but significantly increased SNARK Thr208 phosphorylation. Ischemia also increased SNARK Thr208 phosphorylation, but there was no effect of submaximal or maximal insulin. HL1 cardiomyocytes were used to overexpress wild-type (WT) SNARK and to knockdown endogenous SNARK. Overexpression of WT SNARK had no effect on ischemia-stimulated glucose transport; however, SNARK knockdown significantly decreased ischemia-stimulated glucose transport. SNARK overexpression or knockdown did not alter insulin-stimulated glucose transport or glycogen concentrations. To study SNARK function in vivo, SNARK heterozygous knockout mice (SNARK+/- ) and WT littermates performed treadmill exercise. Exercise-stimulated glucose transport was decreased by ~50% in hearts from SNARK+/- mice. In summary, exercise and ischemia increase SNARK Thr208 phosphorylation in the heart and SNARK regulates exercise-stimulated and ischemia-stimulated glucose transport. SNARK is a novel mediator of insulin-independent glucose transport in the heart.

Association study of polymorphisms in the ABO gene and their gene-gene interactions with ischemic stroke in Chinese population.

AIMS: To investigate the impact of 4 single nucleotide polymorphisms (SNPs) within ABO gene and their gene-gene interactions on ischemic stroke (IS) susceptibility in Chinese Han population. METHODS: A total of 1993 participants (1375 males, 618 females) were selected, including 991 IS patients and 1002 normal controls. The SNPstats (http://bioinfo.iconcologia.net/SNPstats) was used for Hardy-Weinberg equilibrium (HWE) test. Generalized multifactor dimensionality reduction (GMDR) was used to screen the best interaction combination among 4 SNPs within ABO gene. Logistic regression was performed to calculate the ORs (95%CI) for interaction between SNPs. RESULTS: Both rs579459 and rs505922 within ABO gene were associated with IS risk in additive and dominant models. IS risks were higher in those with minor alleles of rs579459 and rs505922 than those with wild-type homozygotes, OR (95%CI) were 1.62 (1.19-2.10) and 1.69 (1.23-2.18), respectively. We did not find any relation of rs651007 and rs529565 with IS risk in both additive and dominant models. GMDR model indicated a significant two-locus model (P = .0010) involving rs505922 and rs579459, indicating a potential interaction between rs505922 and rs579459, the cross-validation consistency of the two-locus models was 9/10, and the testing accuracy was 60.72%. We also found that participants with rs505922- TC/CC and rs579459- TC/CC genotype have the highest IS risk, compared to participants with rs505922- TT and rs579459- TT genotype, OR (95%CI) was 2.94 (1.28-4.66). CONCLUSIONS: We found that rs579459 and rs505922 within ABO gene and their interaction were both associated with increased IS risk in Chinese population.

MicroRNA-455 regulates brown adipogenesis via a novel HIF1an-AMPK-PGC1α signaling network.

Brown adipose tissue (BAT) dissipates chemical energy as heat and can counteract obesity. MicroRNAs are emerging as key regulators in development and disease. Combining microRNA and mRNA microarray profiling followed by bioinformatic analyses, we identified miR-455 as a new regulator of brown adipogenesis. miR-455 exhibits a BAT-specific expression pattern and is induced by cold and the browning inducer BMP7. In vitro gain- and loss-of-function studies show that miR-455 regulates brown adipocyte differentiation and thermogenesis. Adipose-specific miR-455 transgenic mice display marked browning of subcutaneous white fat upon cold exposure. miR-455 activates AMPKα1 by targeting HIF1an, and AMPK promotes the brown adipogenic program and mitochondrial biogenesis. Concomitantly, miR-455 also targets the adipogenic suppressors Runx1t1 and Necdin, initiating adipogenic differentiation. Taken together, the data reveal a novel microRNA-regulated signaling network that controls brown adipogenesis and may be a potential therapeutic target for human metabolic disorders.

The Value of the Score for the Targeting of Atrial Fibrillation (STAF) Screening in Acute Stroke Patients.

BACKGROUND AND PURPOSE: Recently, the score for the targeting of atrial fibrillation (STAF) was introduced to identify the risk of atrial fibrillation (AF) in stroke patients. In this study, we aim to evaluate the usefulness of the STAF score for AF screening in acute stroke patients. METHODS: Patients with acute ischemic stroke who were admitted to our stroke unit were prospectively enrolled from March 2011 to March 2013. Baseline National Institutes of Health Stroke Scale (NIHSS), left atrial dilatation, and vascular etiology were assessed to calculate the STAF score. Logistic regression analysis was used to examine the relationship between AF and STAF factors. Univariate analysis of AF and age, history of coronary heart disease and rheumatic heart disease, NIHSS, left atrial dilatation, and vascular etiology was performed. RESULTS: A total of 472 patients were enrolled in our analysis. AF was documented in 78 (16.53%) patients, of which 50% were paroxysmal. Multivariable analysis demonstrated that age, NIHSS, left atrial dilatation, and the absence of vascular etiology can each function as independent predictors for AF. In addition, all AF patients with a STAF ≥5 show a sensitivity of 76.92% and a specificity of 78.68%. The area under the receiver operating characteristic for all AF patients was .842 versus .763 for the paroxysmal AF (pAF) patients. In addition, a sensitivity of 81% (95% CI 73-92) and a ROC of .829 were for new-AF. CONCLUSIONS: The value of the STAF system for predicting the risk of pAF and new-AF in stroke patients is relatively limited.

Loss of BMP receptor type 1A in murine adipose tissue attenuates age-related onset of insulin resistance.

AIMS/HYPOTHESIS: Adipose tissue dysfunction is a prime risk factor for the development of metabolic disease. Bone morphogenetic proteins (BMPs) have previously been implicated in adipocyte formation. Here, we investigate the role of BMP signalling in adipose tissue health and systemic glucose homeostasis. METHODS: We employed the Cre/loxP system to generate mouse models with conditional ablation of BMP receptor 1A in differentiating and mature adipocytes, as well as tissue-resident myeloid cells. Metabolic variables were assessed by glucose and insulin tolerance testing, insulin-stimulated glucose uptake and gene expression analysis. RESULTS: Conditional deletion of Bmpr1a using the aP2 (also known as Fabp4)-Cre strain resulted in a complex phenotype. Knockout mice were clearly resistant to age-related impairment of insulin sensitivity during normal and high-fat-diet feeding and showed significantly improved insulin-stimulated glucose uptake in brown adipose tissue and skeletal muscle. Moreover, knockouts displayed significant reduction of variables of adipose tissue inflammation. Deletion of Bmpr1a in myeloid cells had no impact on insulin sensitivity, while ablation of Bmpr1a in mature adipocytes partially recapitulated the initial phenotype from aP2-Cre driven deletion. Co-cultivation of macrophages with pre-adipocytes lacking Bmpr1a markedly reduced expression of proinflammatory genes. CONCLUSIONS/INTERPRETATION: Our findings show that altered BMP signalling in adipose tissue affects the tissue's metabolic properties and systemic insulin resistance by altering the pattern of immune cell infiltration. The phenotype is due to ablation of Bmpr1a specifically in pre-adipocytes and maturing adipocytes rather than an immune cell-autonomous effect. Mechanistically, we provide evidence for a BMP-mediated direct crosstalk between pre-adipocytes and macrophages.

[Study on Appraising Storage Periods of Moutan Cortex and Its Quality by Means of Colorimeter].

Objective: To examine the correlation between storage periods and L*, a* and b* color of Moutan Cortex. Methods: A optical density meter was used for the measurement of reflected light from sieved powder and section samples using the CIE 1976 L~*,a~*,b~* color system. The content of paeonol were determined by HPLC. The correlation between storage periods,paeonol content and color indices of Moutan Cortex was analyzed. Results: The measured color was significantly correlated with storage periods. The color of Moutan Cortex shift toward the red with the increase of storage periods. The storage periods were correlated with paeonol content. The measured color was equably correlated with paeonol content. Conclusion: The correlation between the color of Moutan Cortex and storage periods was found in this study. Measurment of the color of Moutan Cortex can be used to appraise its storage periods and quality.

Symptomatic intracerebral hemorrhage after intravenous thrombolysis in Chinese patients: comparison of prediction models.

BACKGROUND: To assess the performance of risk scores in predicting symptomatic intracranial hemorrhage (SICH) after intravenous thrombolysis (IVT). METHODS: A multicenter prospective study was performed in 811 patients who underwent IVT with standard-dose recombinant tissue plasminogen activator within 4.5 hours of acute ischemic stroke (AIS) onset in 67 stroke centers involved in the Thrombolysis Implementation and Monitor of acute ischemic Stroke in China program from May 2007 to April 2012. SEDAN (blood sugar, early infarct signs, [hyper]dense cerebral artery sign, age) score, Safe Implementation of Thrombolysis in Stroke (SITS)-SICH score, Glucose Race Age Sex Pressure Stroke Severity (GRASPS) score, Multicenter Stroke Survey (MSS) score, and Stroke Prognostication using Age and National Institutes of Health Stroke Scale (SPAN)-100 index were calculated in selected patients, and their predictive performance for SICH was compared according to the National Institute of Neurological Disorders and Stroke (NINDS), Safe Implementation of Thrombolysis in Stroke-Monitoring Study (SITS-MOST), and European Cooperative Acute Stroke Study (ECASS)-II criteria. RESULTS: For predicting the risk of SICH (NINDS definition) after IVT, the area under the receiver operating characteristic (ROC) curve of MSS score was the highest (.71, P < .0001). For predicting the risk of SICH (SITS-MOST definition) after IVT, the area under the ROC curve of GRASPS score was the highest (.73, P = .005). For predicting SICH (ECASS-II definition) after IVT, the area under the ROC curve of MSS score was the highest (.73, P < .0001). CONCLUSIONS: SITS-SICH, GRASPS, and MSS scores predicted the risk of SICH after IVT in patients with AIS, but only the latter 2 were better in the Chinese population. MSS score had the best predictive performance for SICH using NINDS and ECASS-II definitions, whereas GRASPS score was the best for SICH using the SITS-MOST definition.

Molecular mechanism by which surface antigen HP0197 mediates host cell attachment in the pathogenic bacteria Streptococcus suis.

Streptococcus suis, one of the most important and prevalent pathogens in swine, presents a major challenge to global public health. HP0197 is an S. suis surface antigen that was previously identified by immunoproteomics and can bind to the host cell surface. Here, we investigated the interaction between HP0197 and the host cell surface glycosaminoglycans (GAGs) using indirect immunofluorescence and cell adhesion inhibition assays. In addition, we determined that a novel 18-kDa domain in the N-terminal region of HP0197 functions as the GAG-binding domain. We then solved the three-dimensional structures of the N-terminal 18-kDa and C-terminal G5 domains using x-ray crystallography. Based on this structural information, the GAG-binding sites in HP0197 were predicted and subsequently verified using site-directed mutagenesis and indirect immunofluorescence. The results indicate that the positively charged residues on the exposed surface of the 18-kDa domain, which are primarily lysines, likely play a critical role in the HP0197-heparin interaction that mediates bacterium-host cell adhesion. Understanding this molecular mechanism may provide a basis for the development of effective drugs and therapeutic strategies for treating streptococcal infections.

Overexpression of TRB3 in muscle alters muscle fiber type and improves exercise capacity in mice.

Increasing evidence suggests that TRB3, a mammalian homolog of Drosophila tribbles, plays an important role in cell growth, differentiation, and metabolism. In the liver, TRB3 binds and inhibits Akt activity, whereas in adipocytes, TRB3 upregulates fatty acid oxidation. In cultured muscle cells, TRB3 has been identified as a potential regulator of insulin signaling. However, little is known about the function and regulation of TRB3 in skeletal muscle in vivo. In the current study, we found that 4 wk of voluntary wheel running (6.6 ± 0.4 km/day) increased TRB3 mRNA by 1.6-fold and protein by 2.5-fold in the triceps muscle. Consistent with this finding, muscle-specific transgenic mice that overexpress TRB3 (TG) had a pronounced increase in exercise capacity compared with wild-type (WT) littermates (TG: 1,535 ± 283; WT: 644 ± 67 joules). The increase in exercise capacity in TRB3 TG mice was not associated with changes in glucose uptake or glycogen levels; however, these mice displayed a dramatic shift toward a more oxidative/fatigue-resistant (type I/IIA) muscle fiber type, including threefold more type I fibers in soleus muscles. Skeletal muscle from TRB3 TG mice had significantly decreased PPARα expression, twofold higher levels of miR208b and miR499, and corresponding increases in the myosin heavy chain isoforms Myh7 and Myb7b, which encode these microRNAs. These findings suggest that TRB3 regulates muscle fiber type via a peroxisome proliferator-activated receptor-α (PPAR-α)-regulated miR499/miR208b pathway, revealing a novel function for TRB3 in the regulation of skeletal muscle fiber type and exercise capacity.

[Research on the characteristics of Ulva prolifera in Shandong Peninsula during 2008-2012 based on MODIS data].

In the present study, the MODIS data were used to monitor the situation of Ulva prolifera in the Shandong Peninsula waters during the period of 2008-2012. Those studies mainly calculate the area of NDVI, and get the information of the time, area , scope , floating path of Ulva prolifera by using threshold segmentation method. The feasibility of monitoring Ulva prolifera information based on MODIS data and the macroscopic regularity of the outburst of Ulva prolifera was elementally studied. The results showed that Ulva prolifera first generated in the middle of May or early June, the time, area, scope of Ulva prolifera reached a maximum, but the relative crowding density was earlier or later when Ulva prolifera developed into a outburst. Finally, Ulva prolifera died away after existing for 71 days in the late July or the early August. Wholly, the floating path moved to the northwest from off the coast to offshore. Based on those aspects above, the outburst of Ulva prolifera in 2008 and 2009 was more serious than others.

Intracranial hypertension as the primary symptom of malignant melanoma: A case report.

BACKGROUND: The etiological diagnosis of intracranial hypertension is quite complicated but important in clinical practice. Some common causes are craniocerebral injury, intracranial space-occupying lesion, subarachnoid hemorrhage, and hydrocephalus. When a patient presents with intracranial hypertension, the common causes are to be considered first so that other causes would be dismissed. With the morbidity lower than 9%, neuromelanin is very rare. Common symptoms include nerve damage symptoms, epilepsy, psychiatric symptoms, and cognitive disorders. CASE SUMMARY: We present a patient with melanoma which manifested with isolated intracranial hypertension without any other neurological signs. A 22-year-old male had repeated nausea and vomiting for 2 mo with Babinski sign (+) on both sides, nuchal rigidity, and subarachnoid hemorrhage. He had been diagnosed with melanoma and was given surgery and whole-brain radiation. Ultimately, the patient died 2 mo later. CONCLUSION: Malignant melanoma should be taken into consideration in the differential diagnosis of intracranial hypertension.

A unique regulator controls the activation threshold of quorum-regulated genes in Pseudomonas aeruginosa.

Quorum-sensing (QS) systems allow organisms, such as the pathogen Pseudomonas aeruginosa, to link gene expression with their population density and the diffusion and flow characteristics of their environment. The leading hypotheses about QS systems' biological functions necessitate that QS-controlled gene expression be suppressed until a threshold culture density (the quorum) is reached. Despite a detailed understanding of QS in P. aeruginosa, known regulatory elements do not fully explain how the quorum threshold for gene activation is produced. Here we investigated the mechanism with a screening approach that used random gene activation. These experiments uncovered a regulator without close homologs in other species that produces the quorum expression threshold. Expression of this regulator (named QteE) reduces LasR protein stability without affecting LasR transcription or translation. QteE also independently reduces RhlR levels. Because QteE can block QS when signal levels are high, it could provide a mechanism for individual cells to exert autonomous control over their QS regulons. This unique regulator governs two central QS control points in P. aeruginosa and shapes the expression pattern thought fundamental to the biological functions of QS.