Boosting the epoxidation of squalene to produce triterpenoids in Saccharomyces cerevisiae.

BACKGROUND: Polycyclic triterpenoids (PTs) are common in plants, and have attracted considerable interest due to their remarkable biological activities. Currently, engineering the ergosterol synthesis pathway in Saccharomyces cerevisiae is a safe and cost-competitive way to produce triterpenoids. However, the strict regulation of ERG1 involved in the epoxidation of squalene limits the triterpenoid production. RESULTS: In this study, we found that the decrease in ERG7 protein level could dramatically boost the epoxidation of squalene by improving the protein stability of ERG1. We next explored the potential factors that affected the degradation process of ERG1 and confirmed that ERG7 was involved in the degradation process of ERG1. Subsequently, expression of four different triterpene cyclases utilizing either 2,3-oxidosqualene or 2,3:22,23-dioxidosqualene as the substrate in ERG7-degraded strains showed that the degradation of ERG7 to prompt the epoxidation of squalene could significantly increase triterpenoid production. To better display the potential of the strategy, we increased the supply of 2,3-oxidosqualene, optimized flux distribution between ergosterol synthesis pathway and ß-amyrin synthesis pathway, and modified the GAL-regulation system to separate the growth stage from the production stage. The best-performing strain ultimately produced 4216.6 ± 68.4 mg/L of ß-amyrin in a two-stage fed-fermentation (a 47-fold improvement over the initial strain). CONCLUSIONS: This study showed that deregulation of the native restriction in ergosterol pathway was an effective strategy to increase triterpenoid production in yeast, which provided a new insight into triterpenoids biosynthesis.

Aging-induced atrial fibrosis in If current change and its effect on atrial fibrillation in dogs.

BACKGROUND: Atrial fibrillation (AF) is a very common type of cardiac arrhythmia that threatens public health. Aging is an independent AF risk factor. However, the mechanism of age-related AF remains unclear. METHODS: A total of 36 Beagle dogs were selected and divided into three groups (12 in each group): two groups were 9-year-old aged dogs, and one group was 4-year-old adult dogs. Electrophysiological testing was employed to determine if modeling is successful. Patch-clamp technique was employed to measure the If current. The expression of protein and mRNA related to If current were also tested. Collagen deposition was observed with the use of Masson staining. RESULTS: Aging resulted in a higher collagen deposition percentage in the left atrium. The hyperpolarization-activated cyclic nucleotide-gated (HCN)2 and HCN4 expressions were increased in the atria and pulmonary veins but decreased in the sinus node of the aged group. Moreover, in the aged group, the left atrium mRNA expressions of Kcnd2 (Potassium voltage-gated channel subfamily D member 2), Kcnh2, Kcnq1, Kcnj2, Kcnj11, and CACNA1H were significantly downregulated. The aged AF group also demonstrated sustained AF and significant changes in electrophysiological characteristics. The If current demonstrated an increased amplitude and was easier to activate in the aged AF group than in younger group. Finally, AF occurrence exacerbated aging-induced cardiac fibrosis, thereby aggravating the above-listed symptoms. CONCLUSION: With age, the increase in atrial fibrosis affected the expression of the ion channels, thereby modulating the If current. Moreover, AF also further exacerbated the degree of atrial fibrosis.

Engineering Saccharomyces cerevisiae for Hyperproduction of ß-Amyrin by Mitigating the Inhibition Effect of Squalene on ß-Amyrin Synthase.

The study aims to enhance ß-amyrin production in Saccharomyces cerevisiae by peroxisome compartmentalization. First, overaccumulated squalene was determined as a key limiting factor for the production of ß-amyrin since it could inhibit the activity of ß-amyrin synthase GgbAs1. Second, to mitigate the inhibition effect, the enhanced squalene synthesis pathway was compartmentalized into peroxisomes to insulate overaccumulated squalene from GgbAs1, and thus the specific titer of ß-amyrin reached 57.8 mg/g dry cell weight (DCW), which was 2.6-fold higher than that of the cytosol engineering strain. Third, by combining peroxisome compartmentalization with the "push-pull-restrain" strategy (ERG1 and GgbAs1 overexpression and ERG7 weakening), the production of ß-amyrin was further increased to 81.0 mg/g DCW (347.0 mg/L). Finally, through fed-batch fermentation in a 5 L fermenter, the titer of ß-amyrin reached 2.6 g/L, which is the highest reported to date. The study provides a new perspective to engineering yeasts as a platform for triterpene production.

A prospective comparison of four methods for preventing pacemaker pocket infections.

This study aims to evaluate four pacemaker pocket cleaning methods for preventing implantation-related infections. This single-center trial prospectively randomized 910 patients undergoing first-time pacemaker implantation or replacement into four pocket cleaning methods: hemocoagulase (group A, n = 228), gentamicin (group B, n = 228), hemocoagulase plus gentamicin (group C, n = 227), and normal saline (group D, n = 227). Before implanting the pacemaker battery, the pockets were cleaned with gauze presoaked in the respective cleaning solutions. Then, these patients were followed up to monitor the occurrence of infections for 1 month after implantation. Twelve implantation-related infections occurred in 910 patients (1.32%): four patients from group A (1.75%), three patients from group B (1.32%), two patients from group C (0.88%), and three patients from group D (1.32%) (P > .05). Furthermore, two patients developed bloodstream infections (0.22%), and both of these patients were associated with pocket infection (one patient was from group A, while the other patient was from group C, respectively). No cases of infective endocarditis occurred. The differences in the number of infections in these study groups were not statistically significant. The application of hemocoagulase, gentamicin, hemocoagulase plus gentamicin, or normal saline on the presoaked gauze before implantation was equally effective in preventing pocket-associated infections.

Renal Denervation Reduced Ventricular Arrhythmia After Myocardial Infarction by Inhibiting Sympathetic Activity and Remodeling.

Background Ventricular arrhythmia after myocardial infarction is the most important risk factor for sudden cardiac death, which poses a serious threat to human health. As the correlation between autonomic nervous systemic dysfunction and heart rhythm abnormality has been gradually revealed, remedies targeting autonomic nervous system dysfunction, especially the sympathetic nerve, have emerged. Among them, renal denervation is noted for its powerful effect on the inhibition of sympathetic nerve activity. We aim to investigate whether renal denervation can reduce ventricular arrhythmia after myocardial infarction and thus decrease the risk of sudden cardiac death. In addition, we explore the potential mechanism with respect to nerve activity and remodeling. Methods and Results Twenty-four beagles were randomized into the control (n=4), renal denervation (n=10), and sham (n=10) groups. Permanent left anterior descending artery ligation was performed to establish myocardial infarction in the latter 2 groups. Animals in the renal denervation group underwent both surgical and chemical renal denervation. Compared with dogs in the sham group, dogs in the renal denervation group demonstrated attenuated effective refractory period shortening and inhomogeneity, flattened restitution curve, increased ventricular threshold, and decreased ventricular arrhythmia. Heart rate variability assessment, catecholamine measurement, and nerve discharge recordings all indicated that renal denervation could reduce whole-body and local tissue sympathetic tone. Tissue analysis revealed a significant decrease in neural remodeling in both the heart and stellate ganglion. Conclusions Surgical and chemical renal denervation decreased whole-body and local tissue sympathetic activity and reversed neural remodeling in the heart and stellate ganglion. Consequently, renal denervation led to beneficial remodeling of the electrophysiological characteristics in the infarction border zone, translating to a decrease in ventricular arrhythmia after myocardial infarction.

TBX18 gene induces adipose-derived stem cells to differentiate into pacemaker-like cells in the myocardial microenvironment.

T-box 18 (TBX18) plays a crucial role in the formation and development of the head of the sinoatrial node. The objective of this study was to induce adipose-derived stem cells (ADSCs) to produce pacemaker-like cells by transfection with the TBX18 gene. A recombinant adenovirus vector carrying the human TBX18 gene was constructed to transfect ADSCs. The ADSCs transfected with TBX18 were considered the TBX18-ADSCs. The control group was the GFP-ADSCs. The transfected cells were co-cultured with neonatal rat ventricular cardiomyocytes (NRVMs). The results showed that the mRNA expression of TBX18 in TBX18-ADSCs was significantly higher than in the control group after 48 h and 7 days. After 7 days of co-culturing with NRVMs, there was no significant difference in the expression of the myocardial marker cardiac troponin I (cTnI) between the two groups. RT-qPCR and western blot analysis showed that the expression of HCN4 was higher in the TBX18-ADSCs than in the GFP-ADSCs. The If current was detected using the whole cell patch clamp technique and was blocked by the specific blocker CsCl. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSCMs) showed approximately twice the current density compared with the ADSCs. Our study indicated that the TBX18 gene induces ADSCs to differentiate into pacemaker­like cells in the cardiac microenvironment. Although further experiments are required in order to assess safety and efficacy prior to implementation in clinical practice, this technique may provide new avenues for the clinical therapy of bradycardia.