ABSTRACT
Lysosomes act as terminal degradation organelles to hydrolyse macromolecules derived from both the extracellular space and the cytoplasm. In Caenorhabditis elegans fasting induces the lysosomal compartment to expand. However, the molecular and cellular mechanisms for this stress response remain largely unclear. In the present study, we find that short-term fasting leads to increased accumulation of polar lipids in lysosomes. The fasting response is co-ordinately regulated by EGL-4, the C. elegans PKG (protein kinase G) orthologue, and nuclear hormone receptor NHR-49. Further results demonstrate that EGL-4 acts in sensory neurons to enhance lysosomal lipid accumulation through inhibiting the DAF-3/SMAD pathway, whereas NHR-49 acts in intestine to inhibit lipids accumulation via activation of IPLA-2 (intracellular membrane-associated calcium-independent phospholipase A2) in cytoplasm and other hydrolases in lysosomes. Remarkably, the lysosomal lipid accumulation is independent of autophagy and RAB-7-mediated endocytosis. Taken together, our results reveal a new mechanism for lysosomal lipid metabolism during the stress response, which may provide new clues for investigations of lysosome function in energy homoeostasis.
Subject(s)
Caenorhabditis elegans Proteins/metabolism , Caenorhabditis elegans/physiology , Cyclic GMP-Dependent Protein Kinases/metabolism , Lipid Metabolism , Lysosomes/metabolism , Receptors, Cytoplasmic and Nuclear/metabolism , Signal Transduction , Stress, Physiological , Animals , Animals, Genetically Modified , Caenorhabditis elegans/enzymology , Caenorhabditis elegans/genetics , Caenorhabditis elegans/ultrastructure , Caenorhabditis elegans Proteins/agonists , Caenorhabditis elegans Proteins/antagonists & inhibitors , Caenorhabditis elegans Proteins/genetics , Cyclic GMP-Dependent Protein Kinases/genetics , Enzyme Activation , Fasting/adverse effects , Hydrolases/chemistry , Hydrolases/genetics , Hydrolases/metabolism , Kinetics , Lysosomes/ultrastructure , Mutation , Nerve Tissue Proteins/agonists , Nerve Tissue Proteins/antagonists & inhibitors , Nerve Tissue Proteins/genetics , Nerve Tissue Proteins/metabolism , Phospholipases A2, Calcium-Independent/chemistry , Phospholipases A2, Calcium-Independent/genetics , Phospholipases A2, Calcium-Independent/metabolism , RNA Interference , Receptors, Cytoplasmic and Nuclear/genetics , Sensory Receptor Cells/enzymology , Sensory Receptor Cells/metabolism , Sensory Receptor Cells/ultrastructure , Smad Proteins/antagonists & inhibitors , Smad Proteins/genetics , Smad Proteins/metabolism , Up-RegulationABSTRACT
AB diblock copolymers comprised of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and poly(3-methacryloxypropyl trimethoxysilane) (PMTSi) segments, which are used for biocompatible coatings, were investigated. Block copolymers with various compositions were synthesized by atomic transfer radical polymerization (ATRP). The obtained copolymers were dissolved in an ethanol solution, and dynamic light scattering showed that all block copolymers were capable of existing as micelles. After a convenient "one-step" reaction, the cellulose membranes could be covalently modified by these copolymers with stable chemical bonds (C-O-Si and Si-O-Si). Block copolymers with different PMPC chain length were applied to surface modification to find the most suitable copolymer. The functional MPC density can be controlled by adjusting the ratio of the two monomers (MPC and MTSi), which also affect surface properties, including the surface contact angle, surface morphology, and number of functional PC groups. The low-fouling properties were measured by protein adsorption, platelet adhesion and activation, and cell adhesion. Protein adsorption of bovine serum albumin (BSA), fibrinogen, and human plasma were also tested and a moderate monomer composite was attained. The protein adsorption behavior on the novel interfaces depends both on MPC density and PMPC chain length. Platelet adhesion and activation were reduced on all the modified surfaces. The adhesion of Human Embryonic Kidney 293 (293T) cells on the coated surfaces also decreased.
Subject(s)
Biocompatible Materials/chemistry , Cellulose/chemistry , Chemistry, Pharmaceutical/methods , Methacrylates/chemistry , Phosphorylcholine/analogs & derivatives , Polymers/chemistry , Silanes/chemistry , Adsorption , Animals , Blood Platelets/drug effects , Cattle , Cell Adhesion , Fibrinogen/chemistry , HEK293 Cells , Humans , Micelles , Phosphorylcholine/chemistry , Platelet Adhesiveness , Proteins/chemistry , Serum Albumin/chemistry , Surface PropertiesABSTRACT
A p-vinylbenzyl sulfobetaine was grafted from cellulose membrane (CM) using surface-initiated atom transfer radical polymerization for blood compatibility improvement. Surface structure, wettability, morphology, and thermal stability of the CM substrates before and after modification were characterized by attenuated total reflectance Fourier transform infrared spectra, X-ray photoelectron spectroscopy measurement, water contact angle measurement, atomic force microscopy, and thermogravimetric analysis, respectively. The results showed that zwitterionic brushes were successfully fabricated on the CM surfaces, and the content of the grafted layer increased gradually with the polymerization time. The blood compatibility of the CM substrates was evaluated by protein adsorption tests and platelet adhesion tests in vitro. It was found that all the CMs functionalized with zwitterionic brush showed improved resistance to nonspecific protein adsorption and platelet adhesion, even though the grafting polymerization was conducted for several minutes.