Autocrine insulin pathway signaling regulates actin dynamics in cell wound repair

Two Septin complexes mediate actin dynamics during cell wound repair

Cells have robust wound repair systems to prevent further damage or infection and to quickly restore cell cortex integrity when exposed to mechanical and chemical stress. Actomyosin ring formation and contraction at the wound edge are major events during closure of the plasma membrane and underlying cytoskeleton during cell wound repair. Here, we show that all five Drosophila Septins are required for efficient cell wound repair. Based on their different recruitment patterns and knockdown/mutant phenotypes, two distinct Septin complexes, Sep1/Sep2/Pnut and Sep4/Sep5/Pnut, are assembled to regulate actin ring assembly, contraction, and remodeling during the repair process. Intriguingly, we find that these two Septin complexes have different F-actin bending activities. In addition, we find that Anillin regulates the recruitment of only one of two Septin complexes upon wounding. Our results demonstrate that two functionally distinct Septin complexes work side by side to discretely regulate actomyosin ring dynamics during cell wound repair.

Tyrosine-phosphorylated DNER sensitizes insulin signaling in hepatic gluconeogenesis by inducing proteasomal degradation of TRB3

OBJECTIVE

Hepatic insulin resistance, which leads to increased hepatic gluconeogenesis, is a major contributor to fasting hyperglycemia in type 2 diabetes mellitus (T2DM). However, the mechanism of impaired insulin-dependent suppression of hepatic gluconeogenesis remains elusive. Delta/Notch-like epidermal growth factor (EGF)-related receptor (DNER), firstly described as a neuron-specific Notch ligand, has been recently identified as a susceptibility gene for T2DM through genome-wide association studies. We herein investigated whether DNER regulates hepatic gluconeogenesis and whether this is mediated by enhanced insulin signaling.

METHODS

The association between DNER, tribbles homolog 3 (TRB3) and Akt signaling was evaluated in C57BL/6J, ob/ob and db/db mice by western blot analysis. DNER loss-of-function and gain-of-function in hepatic gluconeogenesis were analyzed by western blot analysis, quantitative real-time PCR, glucose uptake and output assay in AML-12 cells and partially validated in primary mouse hepatocytes. Hepatic DNER knockdown mice were generated by tail vein injection of adenovirus to confirm the effects of DNER in vivo. The interaction between DNER and TRB3 was investigated by rescue experiments, cycloheximide chase analysis, co-immunoprecipitation and immunofluorescence. The potential insulin-stimulated phosphorylation sites of DNER were determined by co-immunoprecipitation, LC-MS/MS analysis and site-specific mutagenesis.

RESULTS

Here we show that DNER enhanced hepatic insulin signaling in gluconeogenesis by inhibiting TRB3, an endogenous Akt inhibitor, through the ubiquitin-proteasome degradation pathway. In AML-12 hepatocytes, insulin-stimulated activation of Akt and suppression of gluconeogenesis are attenuated by DNER knockdown, but potentiated by DNER over-expression. In C57BL/6J mice, hepatic DNER knockdown is accompanied by impaired glucose and pyruvate tolerance. Furthermore, the in vitro effects of DNER knockdown or over-expression on both Akt activity and hepatic gluconeogenesis can be rescued by TRB3 knockdown or over-expression, respectively. In response to insulin stimulation, DNER interacted directly with insulin receptor and was phosphorylated at Tyr677. This site-specific phosphorylation is essential for DNER to upregulate Akt activity and then downregulate G6Pase and PEPCK expression, by interacting with TRB3 directly and inducing TRB3 proteasome-dependent degradation.

CONCLUSIONS

Taken together, the crosstalk between insulin-Akt and DNER-TRB3 pathways represents a previously unrecognized mechanism by which insulin regulates hepatic gluconeogenesis.

Calcium influx rapidly establishes distinct spatial recruitments of Annexins to cell wounds

To survive daily damage, the formation of actomyosin ring at the wound periphery is required to rapidly close cell wounds. Calcium influx is one of the start signals for these cell wound repair events. Here, we find that rapid recruitment of all three Drosophila calcium responding and phospholipid binding Annexin proteins (AnxB9, AnxB10, AnxB11) to distinct regions around the wound are regulated by the quantity of calcium influx rather than their binding to specific phospholipids. The distinct recruitment patterns of these Annexins regulate the subsequent recruitment of RhoGEF2 and RhoGEF3 through actin stabilization to form a robust actomyosin ring. Surprisingly, we find that reduced extracellular calcium and depletion of intracellular calcium affect cell wound repair differently, despite these two conditions exhibiting similar GCaMP signals. Thus, our results suggest that, in addition to initiating repair events, both the quantity and sources of calcium influx are important for precise Annexin spatiotemporal protein recruitment to cell wounds and efficient wound repair.

Relative quantification of progressive changes in healthy and dysferlin-deficient mouse skeletal muscle proteomes

INTRODUCTION/AIMS

Individuals with dysferlinopathies, a group of genetic muscle diseases, experience delay in the onset of muscle weakness. The cause of this delay and subsequent muscle wasting are unknown, and there are currently no clinical interventions to limit or prevent muscle weakness. To better understand molecular drivers of dysferlinopathies, age-dependent changes in the proteomic profile of skeletal muscle (SM) in wild-type (WT) and dysferlin-deficient mice were identified.

METHODS

Quadriceps were isolated from 6-, 18-, 42-, and 77-wk-old C57BL/6 (WT, Dysf+/+ ) and BLAJ (Dysf-/- ) mice (n = 3, 2 male/1 female or 1 male/2 female, 24 total). Whole-muscle proteomes were characterized using liquid chromatography-mass spectrometry with relative quantification using TMT10plex isobaric labeling. Principle component analysis was utilized to detect age-dependent proteomic differences over the lifespan of, and between, WT and dysferlin-deficient SM. The biological relevance of proteins with significant variation was established using Ingenuity Pathway Analysis.

RESULTS

Over 3200 proteins were identified between 6-, 18-, 42-, and 77-wk-old mice. In total, 46 proteins varied in aging WT SM (p < .01), while 365 varied in dysferlin-deficient SM. However, 569 proteins varied between aged-matched WT and dysferlin-deficient SM. Proteins with significant variation in expression across all comparisons followed distinct temporal trends.

DISCUSSION

Proteins involved in sarcolemma repair and regeneration underwent significant changes in SM over the lifespan of WT mice, while those associated with immune infiltration and inflammation were overly represented over the lifespan of dysferlin-deficient mice. The proteins identified herein are likely to contribute to our overall understanding of SM aging and dysferlinopathy disease progression.

Early Endosomes Act as Local Exocytosis Hubs to Repair Endothelial Membrane Damage

The plasma membrane of a cell is subject to stresses causing ruptures that must be repaired immediately to preserve membrane integrity and ensure cell survival. Yet, the spatio-temporal membrane dynamics at the wound site and the source of the membrane required for wound repair are poorly understood. Here, it is shown that early endosomes, previously only known to function in the uptake of extracellular material and its endocytic transport, are involved in plasma membrane repair in human endothelial cells. Using live-cell imaging and correlative light and electron microscopy, it is demonstrated that membrane injury triggers a previously unknown exocytosis of early endosomes that is induced by Ca²⁺ entering through the wound. This exocytosis is restricted to the vicinity of the wound site and mediated by the endosomal soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) VAMP2, which is crucial for efficient membrane repair. Thus, the newly identified Ca²⁺ -evoked and localized exocytosis of early endosomes supplies the membrane material required for rapid resealing of a damaged plasma membrane, thereby providing the first line of defense against damage in mechanically challenged endothelial cells.

Wrangling Actin Assemblies: Actin Ring Dynamics during Cell Wound Repair

To cope with continuous physiological and environmental stresses, cells of all sizes require an effective wound repair process to seal breaches to their cortex. Once a wound is recognized, the cell must rapidly plug the injury site, reorganize the cytoskeleton and the membrane to pull the wound closed, and finally remodel the cortex to return to homeostasis. Complementary studies using various model organisms have demonstrated the importance and complexity behind the formation and translocation of an actin ring at the wound periphery during the repair process. Proteins such as actin nucleators, actin bundling factors, actin-plasma membrane anchors, and disassembly factors are needed to regulate actin ring dynamics spatially and temporally. Notably, Rho family GTPases have been implicated throughout the repair process, whereas other proteins are required during specific phases. Interestingly, although different models share a similar set of recruited proteins, the way in which they use them to pull the wound closed can differ. Here, we describe what is currently known about the formation, translocation, and remodeling of the actin ring during the cell wound repair process in model organisms, as well as the overall impact of cell wound repair on daily events and its importance to our understanding of certain diseases and the development of therapeutic delivery modalities.

The Actin Regulators Involved in the Function and Related Diseases of Lymphocytes

Actin is an important cytoskeletal protein involved in signal transduction, cell structure and motility. Actin regulators include actin-monomer-binding proteins, Wiskott-Aldrich syndrome (WAS) family of proteins, nucleation proteins, actin filament polymerases and severing proteins. This group of proteins regulate the dynamic changes in actin assembly/disassembly, thus playing an important role in cell motility, intracellular transport, cell division and other basic cellular activities. Lymphocytes are important components of the human immune system, consisting of T-lymphocytes (T cells), B-lymphocytes (B cells) and natural killer cells (NK cells). Lymphocytes are indispensable for both innate and adaptive immunity and cannot function normally without various actin regulators. In this review, we first briefly introduce the structure and fundamental functions of a variety of well-known and newly discovered actin regulators, then we highlight the role of actin regulators in T cell, B cell and NK cell, and finally provide a landscape of various diseases associated with them. This review provides new directions in exploring actin regulators and promotes more precise and effective treatments for related diseases.