Spontaneous transfer of small peripheral peptides between supported lipid bilayer and giant unilamellar vesicles.

Vesicular trafficking facilitates material transport between membrane-bound organelles. Membrane protein cargos are trafficked for relocation, recycling, and degradation during various physiological processes. In vitro fusion studies utilized synthetic lipid membranes to study the molecular mechanisms of vesicular trafficking and to develop synthetic materials mimicking the biological membrane trafficking. Various fusogenic conditions which can induce vesicular fusion have been used to establish synthetic systems that can mimic biological systems. Despite these efforts, the mechanisms underlying vesicular trafficking of membrane proteins remain limited and robust in vitro methods that can construct synthetic trafficking systems for membrane proteins between large membranes (>1 µm2) are unavailable. Here, we provide data to show the spontaneous transfer of small membrane-bound peptides (∼4 kD) between a supported lipid bilayer (SLB) and giant unilamellar vesicles (GUVs). We found that the contact between the SLB and GUVs led to the occasional but notable transfer of membrane-bound peptides in a physiological saline buffer condition (pH 7.4, 150 mM NaCl). Quantitative and dynamic time-lapse analyses suggested that the observed exchange occurred through the formation of hemi-fusion stalks between the SLB and GUVs. Larger protein cargos with a size of ∼77 kD could not be transferred between the SLB and GUVs, suggesting that the larger-sized cargos limited diffusion across the hemi-fusion stalk, which was predicted to have a highly curved structure. Compositional study showed Ni-chelated lipid head group was the essential component catalyzing the process. Our system serves as an example synthetic platform that enables the investigation of small-peptide trafficking between synthetic membranes and reveals hemi-fused lipid bridge formation as a mechanism of peptide transfer.

Impact of Renal Function on Short-Term Outcome After Reperfusion Therapy in Patients With Ischemic Stroke.

BACKGROUND: A high and low estimated glomerular filtration rate (eGFR) could affect outcomes after reperfusion therapy for ischemic stroke. This study aimed to determine whether renal function based on eGFR affects mortality risk in patients with ischemic stroke within 6 months following reperfusion therapy. METHODS: This prospective registry-based cohort study included 2266 patients who received reperfusion therapy between January 2000 and September 2019 and were registered in the SECRET (Selection Criteria in Endovascular Thrombectomy and Thrombolytic Therapy) study or the Yonsei Stroke Cohort. A high and low eGFR were based on the Chronic Kidney Disease Epidemiology Collaboration equation and defined, respectively, as the 5th and 95th percentiles of age- and sex-specific eGFR. Occurrence of death within 6 months was compared among the groups according to their eGFR such as low, normal, or high eGFR. RESULTS: Of the 2266 patients, 2051 (90.5%) had a normal eGFR, 110 (4.9%) a low eGFR, and 105 (4.6%) a high eGFR. Patients with high eGFR were younger or less likely to have hypertension, diabetes, or atrial fibrillation than the other groups. Active cancer was more prevalent in the high-eGFR group. During the 6-month follow-up, there were 24 deaths (22.9%) in the high-eGFR group, 37 (33.6%) in the low-eGFR group, and 237 (11.6%) in the normal-eGFR group. After adjusting for variables with P<0.10 in the univariable analysis, 6-month mortality was independently associated with high eGFR (hazard ratio, 2.22 [95% CI, 1.36-3.62]; P=0.001) and low eGFR (HR, 2.29 [95% CI, 1.41-3.72]; P=0.001). These associations persisted regardless of treatment modality or various baseline characteristics. CONCLUSIONS: High eGFR as well as low eGFR were independently associated with 6-month mortality after reperfusion therapy. Kidney function could be considered a prognostic factor in patients with ischemic stroke after reperfusion therapy.

Early depression screening and short-term functional outcome in hospitalized patients for acute ischemic stroke.

Background: Patients with ischemic stroke are at high risk for post-stroke depression (PSD). There are limited data regarding the clinical impact of early PSD, assessed in hospitalized patients with acute ischemic stroke. Methods: This hospital-based observational cohort study included consecutive patients with acute ischemic stroke or transient ischemic attack between July 2019 and June 2021. In the study hospital, all admitted patients were systematically screened for depression. The depression was screened using the Patient Health Questionnaire-9 (PHQ-9), and PHQ-9 positivity indicated early PSD, which was defined as a score of >4. Logistic regression analyses were used to compare the rates of poor functional outcomes at 3 months in patients with and without PHQ-9 positivity. Results: Among 1339 patients admitted during the study period, 775 were included, with a median age of 68.0 years, and 316 (40.8%) were women. A total of 111 (14.3%) patients were PHQ-9 positive. History of cancer and early neurological deterioration were independently associated with PHQ-9 positivity. Poor functional outcomes at 3 months were observed in 147 patients (18.8%). PHQ-9 positivity independently showed a 2.2-fold increased risk of poor functional outcome at 3 months (Odds ratio 2.23; 95% confidence interval 1.05-4.73, P = 0.037). Conclusions: Patients with history of cancer and early neurological deterioration were at risk for early PSD. Early PSD was independently associated with poor functional outcomes at 3 months. The identification of early depression could offer opportunities for further questioning and exploration of symptoms, as well as interventions.

ATP-dependent force generation and membrane scission by ESCRT-III and Vps4.

The endosomal sorting complexes required for transport (ESCRTs) catalyze reverse-topology scission from the inner face of membrane necks in HIV budding, multivesicular endosome biogenesis, cytokinesis, and other pathways. We encapsulated ESCRT-III subunits Snf7, Vps24, and Vps2 and the AAA+ ATPase (adenosine triphosphatase) Vps4 in giant vesicles from which membrane nanotubes reflecting the correct topology of scission could be pulled. Upon ATP release by photo-uncaging, this system generated forces within the nanotubes that led to membrane scission in a manner dependent upon Vps4 catalytic activity and Vps4 coupling to the ESCRT-III proteins. Imaging of scission revealed Snf7 and Vps4 puncta within nanotubes whose presence followed ATP release, correlated with force generation and nanotube constriction, and preceded scission. These observations directly verify long-standing predictions that ATP-hydrolyzing assemblies of ESCRT-III and Vps4 sever membranes.

Negative membrane curvature catalyzes nucleation of endosomal sorting complex required for transport (ESCRT)-III assembly.

The endosomal sorting complexes required for transport (ESCRT) machinery functions in HIV-1 budding, cytokinesis, multivesicular body biogenesis, and other pathways, in the course of which it interacts with concave membrane necks and bud rims. To test the role of membrane shape in regulating ESCRT assembly, we nanofabricated templates for invaginated supported lipid bilayers. The assembly of the core ESCRT-III subunit CHMP4B/Snf7 is preferentially nucleated in the resulting 100-nm-deep membrane concavities. ESCRT-II and CHMP6 accelerate CHMP4B assembly by increasing the concentration of nucleation seeds. Superresolution imaging was used to visualize CHMP4B/Snf7 concentration in a negatively curved annulus at the rim of the invagination. Although Snf7 assemblies nucleate slowly on flat membranes, outward growth onto the flat membrane is efficiently nucleated at invaginations. The nucleation behavior provides a biophysical explanation for the timing of ESCRT-III recruitment and membrane scission in HIV-1 budding.

Activation-triggered subunit exchange between CaMKII holoenzymes facilitates the spread of kinase activity.

The activation of the dodecameric Ca(2+)/calmodulin dependent kinase II (CaMKII) holoenzyme is critical for memory formation. We now report that CaMKII has a remarkable property, which is that activation of the holoenzyme triggers the exchange of subunits between holoenzymes, including unactivated ones, enabling the calcium-independent phosphorylation of new subunits. We show, using a single-molecule TIRF microscopy technique, that the exchange process is triggered by the activation of CaMKII, and that exchange is modulated by phosphorylation of two residues in the calmodulin-binding segment, Thr 305 and Thr 306. Based on these results, and on the analysis of molecular dynamics simulations, we suggest that the phosphorylated regulatory segment of CaMKII interacts with the central hub of the holoenzyme and weakens its integrity, thereby promoting exchange. Our results have implications for an earlier idea that subunit exchange in CaMKII may have relevance for information storage resulting from brief coincident stimuli during neuronal signaling. DOI: http://dx.doi.org/10.7554/eLife.01610.001.