Insulin induces changes in the subcellular distribution of actin and 5'-nucleotidase

In Vivo Wound-Healing Efficacy of Insulin-Loaded Strontium-Cross-Linked Alginate-Based Hydrogels in Diabetic Rats

The wound-healing effect of insulin is well studied and reported. However, prolonged topical application of insulin without compromising its biological activity is still a challenge. In this study, the effect of topically delivered insulin on promoting wound healing in diabetic animals was evaluated. Alginate diamine PEG-g-poly(PEGMA) (ADPM2S2) was the material used for the topical delivery of insulin. ADPM2S2 hydrogels release insulin and strontium ions, and they synergistically act to regulate different phases of wound healing. Insulin was released from the ADPM2S2 hydrogel for a period of 48 h, maintaining its structural stability and biological activity. In vitro studies were performed under high-glucose conditions to evaluate the wound-healing potential of insulin. Insulin-loaded ADPM2S2 hydrogels showed significant improvement in cell migration, proliferation, and collagen deposition, compared to control cells under high-glucose conditions. Immunostaining studies in L929 cells showed a reduction in phospho Akt expression under high-glucose conditions, and in the presence of insulin, the expression increased. The gene expression studies revealed that insulin plays an important role in regulating the inflammatory phase and macrophage polarization, which favors accelerated wound closure. In vivo experiments in diabetic rat excision wounds treated with insulin-loaded ADPM2S2 showed 95% wound closure within 14 days compared with 82% in control groups. Thus, both the in vitro and in vivo results signify the therapeutic potential of topically delivered insulin in wound management under high-glucose conditions.

Methods to Study Epithelial Transport Protein Function and Expression in Native Intestine and Caco-2 Cells Grown in 3D

The intestinal epithelium has important transport and barrier functions that play key roles in normal physiological functions of the body while providing a barrier to foreign particles. Impaired epithelial transport (ion, nutrient, or drugs) has been associated with many diseases and can have consequences that extend beyond the normal physiological functions of the transporters, such as by influencing epithelial integrity and the gut microbiome. Understanding the function and regulation of transport proteins is critical for the development of improved therapeutic interventions. The biggest challenge in the study of epithelial transport is developing a suitable model system that recapitulates important features of the native intestinal epithelial cells. Several in vitro cell culture models, such as Caco-2, T-84, and HT-29-Cl.19A cells are typically used in epithelial transport research. These cell lines represent a reductionist approach to modeling the epithelium and have been used in many mechanistic studies, including their examination of epithelial-microbial interactions. However, cell monolayers do not accurately reflect cell-cell interactions and the in vivo microenvironment. Cells grown in 3D have shown to be promising models for drug permeability studies. We show that Caco-2 cells in 3D can be used to study epithelial transporters. It is also important that studies in Caco-2 cells are complemented with other models to rule out cell specific effects and to take into account the complexity of the native intestine. Several methods have been previously used to assess the functionality of transporters, such as everted sac and uptake in isolated epithelial cells or in isolated plasma membrane vesicles. Taking into consideration the challenges in the field with respect to models and the measurement of transport function, we demonstrate here a protocol to grow Caco-2 cells in 3D and describe the use of an Ussing chamber as an effective approach to measure serotonin transport, such as in intact polarized intestinal epithelia.

Reactive oxygen species exert opposite effects on Tyr23 phosphorylation of the nuclear and cortical pools of annexin A2

Annexin A2 (AnxA2) is a multi-functional and -compartmental protein whose subcellular localisation and functions are tightly regulated by its post-translational modifications. AnxA2 and its Tyr23-phosphorylated form (pTyr23AnxA2) are involved in malignant cell transformation, metastasis and angiogenesis. Here, we show that H₂O₂ exerts rapid, simultaneous and opposite effects on the Tyr23 phosphorylation status of AnxA2 in two distinct compartments of rat pheochromocytoma (PC12) cells. Reactive oxygen species induce dephosphorylation of pTyr23AnxA2 located in the PML bodies of the nucleus, whereas AnxA2 associated with F-actin at the cell cortex is Tyr23 phosphorylated. The H₂O₂-induced responses in both compartments are transient and the pTyr23AnxA2 accumulating at the cell cortex is subsequently incorporated into vesicles and then released to the extracellular space. Blocking nuclear export by leptomycin B does not affect the nuclear pool of pTyr23AnxA2, but increases the amount of total AnxA2 in this compartment, indicating that the protein might have several functions in the nucleus. These results suggest that Tyr23 phosphorylation can regulate the function of AnxA2 at distinct subcellular sites.

Summary: Reactive oxygen species cause two opposite and transient Tyr23-based modifications of annexin A2; its dephosphorylation in the nucleus and phosphorylation at the cell cortex, resulting in release of the protein in exosomes.

Effects of sperm treatments on the in vitro development of bovine oocytes in semidefined and defined media

Bovine in vitro matured oocytes were inseminated with frozen-thawed spermatozoa prepared by A) swim-up through Fert-TALP supplemented with hyaluronic acid (HYA, 1 mg/ml), heparin (5.0 microg/ml) and bovine serum albumin (BSA, 6 mg/ml) or B) washing by centrifugation in modified Brackett-Oliphant medium (mBO) supplemented with 10 mM caffeine-sodium benzoate. For Method A, in vitro fertilization (IVF) was performed in Fert-TALP supplemented with 6 mg/ml BSA, 5.0 microg/ml heparin, 20 microM D-penicillamine, 10 microM hypotaurine and 1 microM epinephrine. For Method B it was performed in mBO medium supplemented with 10 mg globulin-free BSA/ml and 10 microg heparin/ml. Presumptive zygotes were cultured in 1 of 3 culture media: 1) BSAITS - TCM 199 supplemented with 10 mg/ml BSA and ITS (5 microg/ml insulin, 5 microg/ml transferrin, and 5 ng/ml sodium selenite); 2) BECM - bovine embryo culture medium; and 3) BECM supplemented with ITS. Altogether, a significantly higher proportion of oocytes developed to the blastocyst stage after insemination with spermatozoa prepared by Method A than by Method B (17.9 vs 7.1%, respectively; P < 0.001). For Method A, the cleavage rate and the proportion of zygotes with >2 cells 48 h after insemination did not differ significantly between any of the 3 culture media assayed, but blastocyst formation was significantly stimulated in BSAITS and BECMITS compared with that in BECM (20.7 and 22.1% vs 10.7%, respectively; P < 0.05). For Method B, the cleavage rate and the proportion of zygotes with >2 cells were significantly lower in BSAITS than in BECM and BECMITS (56.4 and 28.7% vs 71.6 and 42.1%; and 70.2 and 51.1%, respectively; P < 0.05). However, no significant differences were recorded in blastocyst development rates between any of the culture media assayed (6.4 to 7.4%; P > 0.05).

Hormones and the cytoskeleton of animals and plants

It is often overlooked that a cell can exert its specific functions only after it has acquired a specific morphology: function follows form. The cytoskeleton plays an important role in establishing this form, and a variety of hormones can influence it. The cytoskeletal framework has also been shown to function in a variety of cellular processes, such as cell motility (important for behavior), migration (important for the interrelationship between the endocrine and immune systems, e.g., chemotaxis), intracellular transport of particles, mitosis and meiosis, maintenance of cellular morphology, spatial distribution of cell organelles (e.g., nucleus and Golgi system), cellular responses to membrane events (e.g., endocytosis and exocytosis), intracellular communication including conductance of electrical signals, localization of mRNA, protein synthesis, and--more specifically in plants--ordered cell wall deposition, cytoplasmic streaming, and spindle function followed by phragmoplast function. All classes of hormones seem to make use of the cytoskeleton, either during their synthesis, transport, secretion, degradation, or when influencing their target cells. In this review special attention is paid to cytoskeleton-mediated effects of selected hormones related to growth, transepithelial transport, steroidogenesis, thyroid and parathyroid functioning, motility, oocyte maturation, and cell elongation in plants.

A serum-free, cell-free culture system for development of bovine one-cell embryos up to blastocyst stage with improved viability

With the aim of developing a serum-free, cell-free culture system for embryo development, in vitro-matured (IVM) and -fertilized (IVF) bovine oocytes were cultured in TCM 199 with the following supplements: 1) BSA alone (10 mg/ml); 2) BSA with ITS (5 mug/ml insulin, 5 mug/ml transferrin and 5 ng/ml selenium; BSAITS medium); 3) estrous cow serum alone (ECS; 10%); or 4) ECS with BOEC (bovine oviduct epithelial cells) (Experiment 1). In Experiment 2, embryos were cultured in BSAITS medium with or without feeding with fresh medium on Day 4 (day of insemination = Day 0). Embryos were evaluated on Day 2 for first cleavage, on Day 7 for morulae and blastocysts, and on Day 8 for blastocysts. Blastocysts from Experiment 1 were frozen in 10% glycerol in PBS, thawed and further cultured in ECS medium with BOEC for 48 h, and evaluated for formation of a distinct blastocoel, or expansion and hatching of blastocysts. In vivo-developed, Grade-1 and Grade-2, 7-d-old embryos served as control for the freezing, thawing and subsequent culture procedures. The percentage of first cleavage did not differ between the treatments (74 to 79% in Experiment 1 and 80 to 83% in Experiment 2). The percentage of blastocysts developed in BSAITS medium did not differ from that in ECS medium whether BOEC were present or not. However, medium with BSA alone had fewer blastocysts than any other culture system (P<0.05). Feeding embryos with fresh BSAITS medium on Day 4 did not lead to any further increase in the proportion of blastocysts. The culture systems had a significant effect on the post-thaw viability of blastocysts developed in them (P<0.001). Blastocysts developed in BSAITS medium had better (P<0.05) viability (14/38) than those from medium with ECS alone (1/27) or with ECS and BOEC (3/37). The post-thaw survival of control embryos was 80% (n=30). One of the three transfers of BSAITS-treated, frozen-thawed blastocysts resulted in a pregnancy. The results indicate that a serum-free, cell-free culture system can support the development of IVM-IVF bovine oocytes up to the blastocyst stage with better viability than a complex co-culture system.

Morphological changes in Krebs II ascites tumour cells induced by insulin are associated with differences in protein composition and altered amounts of free, cytoskeletal-bound and membrane-bound polysomes

A three-step sequential detergent/salt extraction procedure was used in order to isolate three distinct subcellular fractions containing free (FP), cytoskeletal-bound (CBP) and membrane-bound polysomes (MBP), respectively, from Krebs II ascites cells (Vedeler et al., Mol Cell Biochem 100: 183-193, 1991). The purpose was to study changes in the distribution of polysomes in these three fractions during long-term incubation with insulin under either stationary conditions or in roller suspension culture. Insulin caused a redistribution of polysomes between FP, CBP and MBP fractions. The hormone appeared to promote an entry of ribosomes into polysomes both in CBP and MBP populations. When cells were grown in stationary culture in the presence of insulin and thus promoted to attach to the substratum and undergo morphological changes, a diversion of ribosomes from CBP into MBP was observed. The level of protein synthesis was apparently very high in this latter fraction since more than 70% of ribosomes were in polysomes. Morphological changes observed following insulin treatment were accompanied by a shift of certain proteins among subcellular fractions (for example actin and p35). The fibronectin content was about 20% higher in attached compared to non-attached cells. The results suggest that morphological changes induced by stimulation with insulin are associated with an increased activity of MBP, presumably reflecting a requirement for an increased synthesis of membrane proteins.

5'-Nucleotidase: molecular structure and functional aspects

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