Rho/ROCK-dependent inhibition of 3T3-L1 adipogenesis by G-protein-deamidating dermonecrotic toxins: differential regulation of Notch1, Pref1/Dlk1, and β-catenin signaling

GPCR-mediated regulation of beige adipocyte formation: Implications for obesity and metabolic health

Obesity and its associated complications pose a significant burden on health. The non-shivering thermogenesis (NST) and metabolic capacity properties of brown adipose tissue (BAT), which are distinct from those of white adipose tissue (WAT), in combating obesity and its related metabolic diseases has been well documented. However, beige adipose tissue, the third and relatively novel type of adipose tissue, which emerges in extensive presence of WAT and shares similar favorable metabolic properties with BAT, has garnered considerable attention in recent years. In this review, we focused on the role of G protein-coupled receptors (GPCRs), the largest receptor family and the most successful class of drug targets in humans, in the induction of beige adipocytes. More importantly, we highlight researchers' clinical treatment attempts to ameliorate obesity and other related metabolic diseases through the formation and activation of beige adipose tissue. In summary, this review provides valuable insights into the formation of beige adipose tissue and the involvement of GPCRs, based on the latest advancements in scientific research.

Pasteurella multocida toxin - lessons learned from a mitogenic toxin

The gram-negative, zoonotic bacterium Pasteurella multocida was discovered in 1880 and found to be the causative pathogen of fowl cholera. Pasteurella-related diseases can be found in domestic and wild life animals such as buffalo, sheep, goat, deer and antelope, cats, dogs and tigers and cause hemorrhagic septicemia in cattle, rhinitis or pneumonia in rabbits or fowl cholera in poultry and birds. Pasteurella multocida does not play a major role in the immune-competent human host, but can be found after animal bites or in people with close contact to animals. Toxigenic strains are most commonly found in pigs and express a phage-encoded 146 kDa protein, the Pasteurella multocida toxin (PMT). Toxin-expressing strains cause atrophic rhinitis where nasal turbinate bones are destroyed through the inhibition of bone building osteoblasts and the activation of bone resorbing osteoclasts. After its uptake through receptor-mediated endocytosis, PMT specifically targets the alpha subunit of several heterotrimeric G proteins and constitutively activates them through deamidation of a glutamine residue to glutamate in the alpha subunit. This results in cytoskeletal rearrangement, proliferation, differentiation and survival of cells. Because of the toxin's mitogenic effects, it was suggested that it might have carcinogenic properties, however, no link between Pasteurella infections and cell transformation could be established, neither in tissue culture models nor through epidemiological data. In the recent years it was shown that the toxin not only affects bone, but also the heart as well as basically all cells of innate and adaptive immunity. During the last decade the focus of research shifted from signal transduction processes to understanding how the bacteria might benefit from a bone-destroying toxin. The primary function of PMT seems to be the modulation of immune cell activation which at the same time creates an environment permissive for osteoclast formation. While the disease is restricted to pigs, the implications of the findings from PMT research can be used to explore human diseases and have a high translational potential. In this review our current knowledge will be summarized and it will be discussed what can be learned from using PMT as a tool to understand human pathologies.

Effects of the Escherichia coli Bacterial Toxin Cytotoxic Necrotizing Factor 1 on Different Human and Animal Cells: A Systematic Review

Cytotoxic necrotizing factor 1 (CNF1) is a bacterial virulence factor, the target of which is represented by Rho GTPases, small proteins involved in a huge number of crucial cellular processes. CNF1, due to its ability to modulate the activity of Rho GTPases, represents a widely used tool to unravel the role played by these regulatory proteins in different biological processes. In this review, we summarized the data available in the scientific literature concerning the observed in vitro effects induced by CNF1. An article search was performed on electronic bibliographic resources. Screenings were performed of titles, abstracts, and full-texts according to PRISMA guidelines, whereas eligibility criteria were defined for in vitro studies. We identified a total of 299 records by electronic article search and included 76 original peer-reviewed scientific articles reporting morphological or biochemical modifications induced in vitro by soluble CNF1, either recombinant or from pathogenic Escherichia coli extracts highly purified with chromatographic methods. Most of the described CNF1-induced effects on cultured cells are ascribable to the modulating activity of the toxin on Rho GTPases and the consequent effects on actin cytoskeleton organization. All in all, the present review could be a prospectus about the CNF1-induced effects on cultured cells reported so far.

Gα12/13 signaling in metabolic diseases

As the key governors of diverse physiological processes, G protein-coupled receptors (GPCRs) have drawn attention as primary targets for several diseases, including diabetes and cardiovascular disease. Heterotrimeric G proteins converge signals from ~800 members of the GPCR family. Among the members of the G protein α family, the Gα₁₂ family members comprising Gα₁₂ and Gα₁₃ have been referred to as gep oncogenes. Gα_12/13 levels are altered in metabolic organs, including the liver and muscles, in metabolic diseases. The roles of Gα_12/13 in metabolic diseases have been investigated. In this review, we highlight findings demonstrating Gα_12/13 amplifying or dampening regulators of phenotype changes. We discuss the molecular basis of G protein biology in the context of posttranslational modifications to heterotrimeric G proteins and the cell signaling axis. We also highlight findings providing insights into the organ-specific, metabolic and pathological roles of G proteins in changes associated with specific cells, energy homeostasis, glucose metabolism, liver fibrosis and the immune and cardiovascular systems. This review summarizes the currently available knowledge on the importance of Gα_12/13 in the physiology and pathogenesis of metabolic diseases, which is presented according to the basic understanding of their metabolic actions and underlying cellular and molecular bases.

Understanding the activities of two members of a vital category of proteins called G proteins, which initiate metabolic changes when signaling molecules bind to cells, could lead to new therapies for many diseases. Researchers in South Korea and Japan, led by Sang Geon Kim at Seoul National University, review the significance of the Gα12 and Gα13 proteins in diseases characterised by significant changes in metabolism, including liver conditions and disorders of the cardiovascular and immune systems. Specific roles for the proteins have been identified by a variety of methods, including studying the effect of disabling the genes that code for them in mice. Recent insights suggest that drugs interfering with the activity of these Gα proteins might help treat many conditions in which the molecular signalling networks involving the proteins are disrupted.

Adhesion G-protein coupled receptor 56 is required for 3T3-L1 adipogenesis

Obesity-associated conditions represent major global health and financial burdens and understanding processes regulating adipogenesis could lead to novel intervention strategies. This study shows that adhesion G-protein coupled receptor 56 (GPR56) gene transcripts are reduced in abdominal visceral white adipose tissue derived from obese Zucker rats versus lean controls. Immunostaining in 3T3-L1 preadipocytes reveals both mitotic cell restricted surface and low level general expression patterns of Gpr56. Gpr56 transcripts are differentially expressed in 3T3-L1 cells during adipogenesis. Transient knockdown (KD) of Gpr56 in 3T3-L1 cells dramatically inhibits differentiation through reducing the accumulation of both neutral cellular lipids (56%) and production of established adipogenesis Pparγ ₂ (60-80%), C/ebpα (40-78%) mediator, and Ap2 (56-80%) marker proteins. Furthermore, genome editing of Gpr56 in 3T3-L1 cells created CW2.2.4 and RM4.2.5.5 clones (Gpr56 ^-/- cells) with compound heterozygous deletion frameshift mutations which abolish adipogenesis. Genome edited cells have sustained levels of the adipogenesis inhibitor β-catenin, reduced proliferation, reduced adhesion, altered profiles, and or abundance of extracellular matrix component gene transcripts for fibronectin, types I, III, and IV collagens and loss of actin stress fibers. β-catenin KD alone is insufficient to restore adipogenesis in Gpr56 ^-/- cells. Together these data show that Gpr56 is required for adipogenesis in 3T3-L1 cells. This report is the first demonstration that Gpr56 participates in regulation of the adipogenesis developmental program. Modulation of the levels of this protein and/or its biological activity may represent a novel target for development of therapeutic agents for the treatment of obesity.

Anti-adipogenic effects of KD025 (SLx-2119), a ROCK2-specific inhibitor, in 3T3-L1 cells

Adipose tissue is a specialized organ that synthesizes and stores fat. During adipogenesis, Rho and Rho-associated kinase (ROCK) 2 are inactivated, which enhances the expression of pro-adipogenic genes and induces the loss of actin stress fibers. Furthermore, pan ROCK inhibitors enhance adipogenesis in 3T3-L1 cells. Here, we show that KD025 (formerly known as SLx-2119), a ROCK2-specific inhibitor, suppresses adipogenesis in 3T3-L1 cells partially through a ROCK2-independent mechanism. KD025 downregulated the expression of key adipogenic transcription factors PPARγ and C/EBPα during adipogenesis in addition to lipogenic factors FABP4 and Glut4. Interestingly, adipogenesis was blocked by KD025 during days 1~3 of differentiation; after differentiation terminated, lipid accumulation was unaffected. Clonal expansion occurred normally in KD025-treated cells. These results suggest that KD025 could function during the intermediate stage after clonal expansion. Data from depletion of ROCKs showed that KD025 suppressed cell differentiation partially independent of ROCK’s activity. Furthermore, no further loss of actin stress fibers emerged in KD025-treated cells during and after differentiation compared to control cells. These results indicate that in contrast to the pro-adipogenic effect of pan-inhibitors, KD025 suppresses adipogenesis in 3T3-L1 cells by regulating key pro-adipogenic factors. This outcome further implies that KD025 could be a potential anti-adipogenic/obesity agent.

Selective Membrane Redistribution and Depletion of Gαq-Protein by Pasteurella multocida Toxin

Pasteurella multocida toxin (PMT), the major virulence factor responsible for zoonotic atrophic rhinitis, is a protein deamidase that activates the alpha subunit of heterotrimeric G proteins. Initial activation of G alpha-q-coupled phospholipase C-beta-1 signaling by PMT is followed by uncoupling of G alpha-q-dependent signaling, causing downregulation of downstream calcium and mitogenic signaling pathways. Here, we show that PMT decreases endogenous and exogenously expressed G alpha-q protein content in host cell plasma membranes and in detergent resistant membrane (DRM) fractions. This membrane depletion of G alpha-q protein was dependent upon the catalytic activity of PMT. Results indicate that PMT-modified G alpha-q redistributes within the host cell membrane from the DRM fraction into the soluble membrane and cytosolic fractions. In contrast, PMT had no affect on G alpha-s or G beta protein levels, which are not substrate targets of PMT. PMT also had no affect on G alpha-11 levels, even though G alpha-11 can serve as a substrate for deamidation by PMT, suggesting that membrane depletion of PMT-modified G-alpha-q has specificity.

miR-125a-3p and miR-483-5p promote adipogenesis via suppressing the RhoA/ROCK1/ERK1/2 pathway in multiple symmetric lipomatosis

Multiple symmetric lipomatosis (MSL) is a rare disease characterized by symmetric and abnormal distribution of subcutaneous adipose tissue (SAT); however, the etiology is largely unknown. We report here that miR-125a-3p and miR-483-5p are upregulated in the SAT of MSL patients, promoting adipogenesis through suppressing the RhoA/ROCK1/ERK1/2 pathway. TaqMan microRNA (miR) array analysis revealed that 18 miRs were upregulated in the SAT of MSL patients. Transfection of human adipose-derived mesenchymal stem cells (hADSCs) with the individual agomirs of these 18 miRs showed that miR-125a-3p and miR-483-5p significantly promoted adipogenesis. A dual-luciferase assay showed that RhoA and ERK1 were the targets of miR-125a-3p and miR-483-5p, respectively. Moreover, transfection of hADSCs with mimics of miR-125a-3p and miR-483-5p resulted in a pronounced decrease of ERK1/2 phosphorylation in the nucleus; conversely, transfection of hADSCs with inhibitors of miR-125a-3p and miR-483-5p led to a significant increase of ERK1/2 phosphorylation in the nucleus. Most importantly, we found that miR-125a-3p and miR-483-5p promoted de novo adipose tissue formation in nude mice. These results demonstrated that miR-125a-3p and miR-483-5p coordinately promoted adipogenesis through suppressing the RhoA/ROCK1/ERK1/2 pathway. Our findings may provide novel strategies for the management and treatment of MSL or obesity.

Pasteurella multocida: from zoonosis to cellular microbiology

In a world where most emerging and reemerging infectious diseases are zoonotic in nature and our contacts with both domestic and wild animals abound, there is growing awareness of the potential for human acquisition of animal diseases. Like other Pasteurellaceae, Pasteurella species are highly prevalent among animal populations, where they are often found as part of the normal microbiota of the oral, nasopharyngeal, and upper respiratory tracts. Many Pasteurella species are opportunistic pathogens that can cause endemic disease and are associated increasingly with epizootic outbreaks. Zoonotic transmission to humans usually occurs through animal bites or contact with nasal secretions, with P. multocida being the most prevalent isolate observed in human infections. Here we review recent comparative genomics and molecular pathogenesis studies that have advanced our understanding of the multiple virulence mechanisms employed by Pasteurella species to establish acute and chronic infections. We also summarize efforts being explored to enhance our ability to rapidly and accurately identify and distinguish among clinical isolates and to control pasteurellosis by improved development of new vaccines and treatment regimens.