A Suitable Membrane Distance Regulated by the RBD_ACE2 Interaction is Critical for SARS-CoV-2 Spike-Mediated Viral Invasion

The receptor-binding domain (RBD) of spike recognizing the receptor angiotensin-converting enzyme 2 (ACE2) initiates membrane fusion between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and cell membrane. Although the structure of the RBD_ACE2 complex has been well studied, its functional mechanism in membrane fusion is still not fully understood. Here, using an in vitro cell-vesicle content-mixing assay, it is found that the cleavage at the S2' site by thrombin (Thr) protease strongly accelerates membrane fusion, compared to that of cleavage at the S1/S2 site by PreScission (3C) protease. Moreover, mutations at the RBD_ACE2 interface resulted in a positive correlation between binding affinity and fusion probability. In both the cell-vesicle and cell-cell fusion assays, by crosslinking two membranes via the neutravidin (NTV)_biotin interaction or complementary DNA strands, it is found that spike drives membrane fusion in the absence of ACE2, and a suitable distance between two membranes is critical for spike-mediated membrane fusion. Finally, unsuitable membrane crosslinkers significantly inhibited the fusion probability in the presence of ACE2. Taken together, the results suggest that the RBD_ACE2 complex may act as a crosslinker to bridge the viral and cell membranes at a suitable distance, which is critical, but also substitutable for spike-mediated SARS-CoV-2 entry.

Vesicle trafficking and vesicle fusion: mechanisms, biological functions, and their implications for potential disease therapy

Intracellular vesicle trafficking is the fundamental process to maintain the homeostasis of membrane-enclosed organelles in eukaryotic cells. These organelles transport cargo from the donor membrane to the target membrane through the cargo containing vesicles. Vesicle trafficking pathway includes vesicle formation from the donor membrane, vesicle transport, and vesicle fusion with the target membrane. Coat protein mediated vesicle formation is a delicate membrane budding process for cargo molecules selection and package into vesicle carriers. Vesicle transport is a dynamic and specific process for the cargo containing vesicles translocation from the donor membrane to the target membrane. This process requires a group of conserved proteins such as Rab GTPases, motor adaptors, and motor proteins to ensure vesicle transport along cytoskeletal track. Soluble N-ethyl-maleimide-sensitive factor (NSF) attachment protein receptors (SNARE)-mediated vesicle fusion is the final process for vesicle unloading the cargo molecules at the target membrane. To ensure vesicle fusion occurring at a defined position and time pattern in eukaryotic cell, multiple fusogenic proteins, such as synaptotagmin (Syt), complexin (Cpx), Munc13, Munc18 and other tethering factors, cooperate together to precisely regulate the process of vesicle fusion. Dysfunctions of the fusogenic proteins in SNARE-mediated vesicle fusion are closely related to many diseases. Recent studies have suggested that stimulated membrane fusion can be manipulated pharmacologically via disruption the interface between the SNARE complex and Ca²⁺ sensor protein. Here, we summarize recent insights into the molecular mechanisms of vesicle trafficking, and implications for the development of new therapeutics based on the manipulation of vesicle fusion.

[Association of abnormal metabolic indices and its clustering with carotid intima-media thickness in childhood]

Objective: To examine the association of abnormal metabolic indexes and its clustering with carotid intima-media thickness (cIMT) in childhood. Methods: A convenient sampling method was used to conduct a cross-sectional survey from November 2017 to January 2018 in a primary school in Huantai County, Zibo City, Shandong Province. A total of 1 240 children who had complete data of questionnaires, physical examinations, and blood biochemical tests were included for analysis. Covariance analysis was used to analyze the association of the single abnormal metabolic indices and its clustering with cIMT. The multivariable linear regression model was used to quantify the relationship between the number of abnormal metabolic indices and cIMT. Results: The age of 1 240 children was (8.9±1.5) years, and 657 boys accounted for 53.0%. The highest detection rate of abnormal metabolic indicators was found in abdominal obesity, accounting for 30.9% (203/657) of boys and 29.7% (173/583) girls respectively.The cIMT of boys and girls were (0.49±0.08) and (0.45±0.07) mm, respectively. After adjusting for sex, age, consumption of fruits, vegetables and carbonated drinks, sleep duration, screen time and physical activity, abdominal obesity, elevated blood pressure, total triglyceride and fasting glucose were associated with cIMT (all P values <0.001). Children with 0, 1, 2 and ≥3 abnormal metabolic indicators had cIMT values of (0.45±0.07), (0.48±0.08), (0.50±0.09) and (0.53±0.08) mm, respectively. That was, cIMT values increased with the number of abnormal metabolic indexes (P(trend)<0.001). Conclusion: Abdominal obesity, elevated blood pressure, total triglyceride, fasting glucose and clustering of the above factors are associated with cIMT.

[Operative treatment of delayed acetabular fractures through combined anterior and Kocher-Langenbeck approaches]

Objective: To discuss the clinical outcomes of treating delayed acetabular fractures by combined anterior and posterior approach. Methods: A retrospective analysis was conducted of 31 delayed acetabular fractures from February 2012 to February 2017 in the First Affiliated Hospital of Chongqing Medical University, including 18 males and 13 females with age of 48.5 years(23 to 67 years) .The injury to the operation time was 35.9 days(22 to 183 days). Of these 31 cases, there were 6 cases of transverse and posterior wall fracture, 8 cases with anterior column+ posterior half transverse fracture, 12 cases with double column fracture and 5 cases of "T" type fracture according to Letournel-Judet classification.All fractures were treated combined anterior and Kocher-Langenbeck approaches, including 13 cases of ilioinguinal approach+ Kocher-Langenbeck(K-L approach), 4 cases of extensile acetabular approach, 7 cases of stoppa approach + K-L approach and 7 cases of side rectus femoris approach.Correlation was analyzed by Pearson correlation regression testing. Results: Follow up to August 2017, all patients were followed up with 36.0 months(from 6 to 55 months). As calculated, the restorational effect was positively with result of the X-ray film and the clinical effect(r=0.823, 0.856; both P<0.05). The evaluation was conducted with Matta's reduction criteria: there were 11 cases classified as anatomic reduction(35.5%), 13 cases as satisfactory reduction(41.9%), and 7 cases as unsatisfactory reduction(22.6%). Excellent and good rate was 77.4%. Functional reductions were categorized by the standard of Matta hip score: 8 excellent cases(25.8%), 11 good cases(35.5%), 8 fail cases(25.8%), and 4 poor cases(12.9%). Conclusion: The treatment of delayed acetabular fracture by combined anterior and posterior approach can fully exposure the anterior and posterior acetabular fcloumns, which is beneficial to the release and fixation of the old acetabular fractures.

[Application of computer image process to the research on the contact characteristics of subtalar joint]

With the use of computer image processing technology, a new method was proposed for studying the contact characteristics of the subtalar joint. The results showed the total subtalar articulation area was 9.52 +/- 0.40 cm2. On neutral position and under 600 N load, the contact area of the subtalar joint was 2.00 +/- 0.11 cm2. The contact area of the posterior articulation was significantly larger than that of the anterior and medial articulation (p < 0.01). The average contact pressure was 19.3 +/- 1.38 N, the force transmitted by the subtalar was 389.16 +/- 28.75 N, which accounted for about 64.86% of the applied shank load (600 N), and 69.39% of the force was transmitted by the posterior articulation. The posterior articulation plays an important role in the load. The fracture line of the calcaneus often appears in this area.

Validation of a model predicting enrollment status in a chemoprevention trial for breast cancer

We evaluated the performance of a regression model in predicting enrollment status in a chemoprevention trial for breast cancer using a population independent of that from which the model was derived. In years 1 and 2 of recruitment, questionnaires were completed by eligible participants following attendance at informational meetings about the Breast Cancer Prevention Trial. The variables in the original model, based on women recruited in year 1, included not being able to take estrogen replacement therapy (ERT), concern about the side effects of tamoxifen, the possibility of getting a placebo, the out-of-pocket expenses associated with the trial, and disagreement with the statement "significant others would be reassured if the respondent was taking tamoxifen." These variables were used to predict enrollment status of women newly recruited to the trial in year 2. Among the 89 women in the study population who responded to the questionnaire, 66% did not enroll in the trial. By applying the original logistic regression model, enrollment status in the trial was correctly predicted for 72% of year 2 questionnaire respondents. Age and risk scores, as binary variables, were used in a derived logistic model to determine whether they provided additional predictive information on enrollment status. The resulting four-factor model, which predicted nonenrollment, included: age of > or = 50 years, not being able to take ERT, expressed concern that significant others would not be reassured if the respondent was taking tamoxifen, and concern about out-of-pocket expenses associated with the trial. This model correctly classified 76% of the respondents. The logistic regression models performed reasonably well in predicting enrollment status. Not being able to take ERT remained the strongest factor predicting nonenrollment. More research is needed to evaluate factors that motivate persons to seek participation in primary chemoprevention trials in culturally diverse populations.

[Experimental study on mechanism of xiukeyin in anti-bacterial translocation from gut]

OBJECTIVE

To provide a TCM therapeutic base for treatment of critical multiple organ failure (MOF) patients clinically, the mechanism of Xiukeyin (XKY, Shock Beverage) in anti-bacterial translocation from gut in rats was studied.

METHODS

Based on the pathophysiology of MOF following severe injury, such as shock caused enterogenous-sepsis and bacterial translocation from gut, a hemorrhagic shock model of rat was established and used to determine the effect of XKY on anti-bacterial translocation. XKY was formulated by modifying Wenpi Decoction.

RESULTS

The incidence of intestinal bacterial translocation to mesenteric lymph nodes, liver and spleen was lower in the model rats infused via gastrogavage with XKY (3/15) than that in the noninfused rats (11/13) (P < 0.01). The amount and species of intestinal flora in XKY infused or noninfused rats were not different statistically (P > 0.05). Histological examination showed that the intestinal edema was severer in the model group than that in the XKY treated group.

CONCLUSIONS

XKY could inhibit the shock induced enterogenous bacterial translocation, the mechanism might be due to its protective action on intestinal mucosa. XKY showed no effect on the growth of intestinal bacteria.