Real-time visualization of exo- and endocytosis membrane dynamics with confocal and super-resolution microscopy

Clathrin mediates membrane fission and budding by constricting membrane pores

Membrane budding, which underlies fundamental processes like endocytosis, intracellular trafficking, and viral infection, is thought to involve membrane coat-forming proteins, including the most observed clathrin, to form Ω-shape profiles and helix-forming proteins like dynamin to constrict Ω-profiles' pores and thus mediate fission. Challenging this fundamental concept, we report that polymerized clathrin is required for Ω-profiles' pore closure and that clathrin around Ω-profiles' base/pore region mediates pore constriction/closure in neuroendocrine chromaffin cells. Mathematical modeling suggests that clathrin polymerization at Ω-profiles' base/pore region generates forces from its intrinsically curved shape to constrict/close the pore. This new fission function may exert broader impacts than clathrin's well-known coat-forming function during clathrin (coat)-dependent endocytosis, because it underlies not only clathrin (coat)-dependent endocytosis, but also diverse endocytic modes, including ultrafast, fast, slow, bulk, and overshoot endocytosis previously considered clathrin (coat)-independent in chromaffin cells. It mediates kiss-and-run fusion (fusion pore closure) previously considered bona fide clathrin-independent, and limits the vesicular content release rate. Furthermore, analogous to results in chromaffin cells, we found that clathrin is essential for fast and slow endocytosis at hippocampal synapses where clathrin was previously considered dispensable, suggesting clathrin in mediating synaptic vesicle endocytosis and fission. These results suggest that clathrin and likely other intrinsically curved coat proteins are a new class of fission proteins underlying vesicle budding and fusion. The half-a-century concept and studies that attribute vesicle-coat contents' function to Ω-profile formation and classify budding as coat-protein (e.g., clathrin)-dependent or -independent may need to be re-defined and re-examined by considering clathrin's pivotal role in pore constriction/closure.

Membrane transformations of fusion and budding

Membrane fusion and budding mediate fundamental processes like intracellular trafficking, exocytosis, and endocytosis. Fusion is thought to open a nanometer-range pore that may subsequently close or dilate irreversibly, whereas budding transforms flat membranes into vesicles. Reviewing recent breakthroughs in real-time visualization of membrane transformations well exceeding this classical view, we synthesize a new model and describe its underlying mechanistic principles and functions. Fusion involves hemi-to-full fusion, pore expansion, constriction and/or closure while fusing vesicles may shrink, enlarge, or receive another vesicle fusion; endocytosis follows exocytosis primarily by closing Ω-shaped profiles pre-formed through the flat-to-Λ-to-Ω-shape transition or formed via fusion. Calcium/SNARE-dependent fusion machinery, cytoskeleton-dependent membrane tension, osmotic pressure, calcium/dynamin-dependent fission machinery, and actin/dynamin-dependent force machinery work together to generate fusion and budding modes differing in pore status, vesicle size, speed and quantity, controls release probability, synchronization and content release rates/amounts, and underlies exo-endocytosis coupling to maintain membrane homeostasis. These transformations, underlying mechanisms, and functions may be conserved for fusion and budding in general.

5-Fluorouracil and Anti-EGFR antibody scaffold chitosan-stabilized Pickering emulsion: Formulations, physical characterization, in-vitro studies in NCL-H226 cells, and in-vivo investigations in Wistar rats for the augmented therapeutic effects against squamous cell carcinoma

This research seeks to optimize a chitosan-stabilized Pickering emulsion (PE) containing 5-fluorouracil (5-FU) as a potential Squamous Cell Carcinoma therapy. The 5-Fluorouracil was also thoroughly analysed using UV spectrophotometry and RP-HPLC, demonstrating exceptional linearity, sensitivity, precision, and robustness. The techniques of characterization revealed Pickering emulsion (PE) morphology, solid-like gel properties, successful encapsulation, and promising anticancer effects. FTIR was used to validate the efficacy of encapsulation, and DSC was used to confirm the post-encapsulation drug stability. The 0.6 % chitosan-stabilized PE showed exceptional stability and drug loading efficiency. Anti-EGFR-5-FU-CS-PE gel was developed for sustained drug release in the treatment of Squamous Cell Carcinoma. Anti-EGFR-5-FU-CS-PE demonstrated potent anticancer effects in vitro, with a lower IC50 than 5-FU and 5-FU-CS-PE. Anti-EGFR-5-FU-PE Pickering emulsions based on chitosan were investigated for their rheological properties, cellular interactions, and therapeutic potential. Both emulsions and gel exhibited sustained in vitro drug release after successful encapsulation. Anti-EGFR-5-FU-CS-PE induced apoptosis, decreased mitochondrial membrane potential, and inhibited the migration of cancer cells. Wistar mice were tested for safety and tumour growth inhibition. All formulations exhibited exceptional six-month stability. Anti-EGFR-5-FU-CS-PE emerges as a viable therapeutic option, necessitating additional research.