A role for prohibitin in mast cell activation: location matters

Prohibitions in the meta-inflammatory response: a review

Prohibitins are the central regulatory element of cellular homeostasis, especially by modulating the response at different levels: Nucleus, mitochondria and membranes. Their localization and interaction with various proteins, homons, transcription and nuclear factors, and mtDNA indicate the globality and complexity of their pleiotropic properties, which remain to be investigated. A more detailed deciphering of cellular metabolism in relation to prohibitins under normal conditions and in various metabolic diseases will allow us to understand the precise role of prohibitins in the signaling cascades of PI3K/Akt, Raf/MAP/ERK, STAT3, p53, and others and to fathom their mutual influence. A valuable research perspective is to investigate the role of prohibitins in the molecular and cellular interactions between the two major players in the pathogenesis of obesity-adipocytes and macrophages - that form the basis of the meta-inflammatory response. Investigating the subtle intercellular communication and molecular cascades triggered in these cells will allow us to propose new therapeutic strategies to eliminate persistent inflammation, taking into account novel molecular genetic approaches to activate/inactivate prohibitins.

Therapeutic anti-amyloid β antibodies cause neuronal disturbances

INTRODUCTION

Recent published clinical trial safety data showed that 41% of Alzheimer patients experienced amyloid-related imaging abnormalities (ARIA), marks of microhemorrhages and edema in the brain, following administration of Biogen's Aduhelm/aducanumab (amino acids 3-7 of the Aβ peptide). Similarly, Janssen/Pfizer's Bapineuzumab (amino acids 1-5 of the Aβ peptide) and Roche's Gantenerumab (amino acids 2-11/18-27 of the Aβ peptide) also displayed ARIA in clinical trials, including microhemorrhage and focal areas of inflammation or vasogenic edema, respectively. The molecular mechanisms underlying ARIA caused by therapeutic anti-Aβ antibodies remain largely unknown, however, recent reports demonstrated that therapeutic anti-prion antibodies activate neuronal allergenic proteomes following cross-linking cellular prion protein.

METHODS

Here, we report that treatment of human induced pluripotent stem cells- derived neurons (HSCN) from a non-demented donor, co-cultured with human primary microglia with anti-Aβ1-6, or anti-Aβ17-23 antibodies activate a significant number of allergenic-related proteins as assessed by mass spectrometry.

RESULTS

Interestingly, a large proportion of the identified proteins included cytokines such as interleukin (IL)-4, IL-12, and IL-13 suggesting a type-1 hypersensitivity response. Following flow cytometry analysis, several proinflammatory cytokines were significantly elevated following anti-Aβ1-6, or anti-Aβ17-23 antibody treatment.

DISCUSSION

These results justify further and more robust investigation of the molecular mechanisms of ARIA during immunotherapy study trials of AD.

HIGHLIGHTS

Allergenic-related proteins are often linked with Alzheimer's disease (AD). We investigated the effects of amyloid beta (Aβ) immunotherapy on stem cell derived neurons and primary neuronal cells co-cultured with microglia. Anti-Aβ antibody treatment of neurons or neurons co-cultured with microglia led to activation of a substantial number of allergenic-related genes. These allergenic-related genes are associated with endothelial dysfunction possibly responsible for ARIA.

Prohibitin 2/PHB2 in Parkin-Mediated Mitophagy: A Potential Therapeutic Target for Non-Small Cell Lung Carcinoma

Background

Mitophagy, a selective autophagy process, plays various roles in tumors. Prohibitin 2 (PHB2) is an inner-mitochondrial membrane protein that participates in parkin-induced mitophagy. However, the role of PHB2 in non-small cell lung carcinoma (NSCLC) has not been previously reported.

Material/Methods

PHB2 protein or PHB2-mRNA in NSCLC and paired normal tissues was determined by Western blot, qRT-PCR, and immunohistochemical staining. Cell proliferation was detected by CCK-8 assay. Cell migration was evaluated by wound healing and transwell migration assays. A 3D live-cell confocal system was used to monitor autophagic flux. Mitochondrial autolysosomes were observed by transmission electron microscopy (TEM). Finally, we performed JC-1 assay to measure mitochondrial membrane potential (MMP).

Results

The level of PHB2 was significantly increased in human NSCLC specimens compared to paired adjacent specimens. Inhibition of PHB2 expression attenuated mitophagy in A549 and H1299 cells, as indicated by decreased levels of LC3 II/I and parkin markers and increased level of p62 protein. Furthermore, the inhibition caused reduction in mitochondrial autolysosomes and autophagic flux, as shown by TEM and live-cell imaging, respectively. In addition, PHB2 inhibition caused a remarkable increase in MMP and suppressed the proliferation and migration of A549 and H1299 cells.

Conclusions

Our results suggest that downregulation of PHB2 reduced parkin-mediated mitophagy, which suppressed proliferation and migration of A549 and H1299 cells.

The role of lipid raft translocation of prohibitin in regulation of Akt and Raf-protected apoptosis of HaCaT cells upon ultraviolet B irradiation

Prohibitin (PHB) plays a role in regulation of ultraviolet B light (UVB)-induced apoptosis of human keratinocytes, HaCaT cells. The regulatory function of PHB appears to be associated with its lipid raft translocation. However, the detailed mechanism for PHB-mediated apoptosis of these keratinocytes upon UVB irradiation is not clear. In this report, we determined the role of lipid raft translocation of PHB in regulation of UVB-induced apoptosis. Our data show that upon UVB irradiation PHB is translocated from the non-raft membrane to the lipid rafts, which is correlated with a release of both Akt and Raf from membrane. Overexpression of Akt and/or Raf impedes UVB-induced lipid raft translocation of PHB. Immunoprecipitation analysis indicates that UVB alters the interactions among PHB, Akt, and Raf. Reduced expression of PHB leads to a decreased phosphorylation of Akt and ERK, as well as a decreased activity of Akt, and increased apoptosis of the cells upon UVB irradiation. These results suggest that PHB regulates UVB-induced apoptosis of keratinocytes via a mechanism that involves detachment from Akt and Raf on the plasma membrane, and sequential lipid raft translocation.

Prohibitin confers cytoprotection against ISO-induced hypertrophy in H9c2 cells via attenuation of oxidative stress and modulation of Akt/Gsk-3β signaling

Numerous hypertrophic stimuli, including β-adrenergic agonists such as isoproterenol (ISO), result in generation of reactive oxygen species (ROS) and alteration in the mitochondrial membrane potential (Δψ) leading to oxidative stress. This process is well associated with phosphorylation of thymoma viral proto-oncogene Akt (Ser473) and glycogen synthase kinase-3β (Gsk-3β) (Ser9), with resultant inactivation of Gsk-3β. In the present study, we found that the protective defensive role of prohibitin (PHB) against ISO-induced hypertrophic response in rat H9c2 cells is via attenuation of oxidative stress-dependent signaling pathways. The intracellular levels of mitochondrial membrane potential along with cellular ROS levels and mitochondrial superoxide generation were determined. In order to understand the regulation of Akt/Gsk-3β signaling pathway, we carried out immmunoblotting for key proteins of the pathway such as PTEN, PI3K, phosphorylated, and unphosphorylated forms of Akt, Gsk-3β, and immunofluorescence experiments of p-Gsk-3β. Enforced expression of PHB in ISO-treated H9c2 cells suppressed cellular ROS production with mitochondrial superoxide generation and enhanced the mitochondrial membrane potential resulting in suppression of oxidative stress which likely offered potent cellular protection, led to the availability of more healthy cells, and also, significant constitutive activation of Gsk-3β via inactivation of Akt was observed. Knockdown of PHB expression using PHB siRNA in control H9c2 cells reversed these effects. Overall, our results demonstrate that PHB confers cytoprotection against oxidative stress in ISO-induced hypertrophy and this process is associated with modulation of Akt/Gsk-3β signaling mechanisms as evident from our PHB overexpression and knockdown experiments.

Spatial mapping of juxtacrine axo-glial interactions identifies novel molecules in peripheral myelination

Cell–cell interactions promote juxtacrine signals in specific subcellular domains, which are difficult to capture in the complexity of the nervous system. For example, contact between axons and Schwann cells triggers signals required for radial sorting and myelination. Failure in this interaction causes dysmyelination and axonal degeneration. Despite its importance, few molecules at the axo-glial surface are known. To identify novel molecules in axo-glial interactions, we modified the ‘pseudopodia' sub-fractionation system and isolated the projections that glia extend when they receive juxtacrine signals from axons. By proteomics we identified the signalling networks present at the glial-leading edge, and novel proteins, including members of the Prohibitin family. Glial-specific deletion of Prohibitin-2 in mice impairs axo-glial interactions and myelination. We thus validate a novel method to model morphogenesis and juxtacrine signalling, provide insights into the molecular organization of the axo-glial contact, and identify a novel class of molecules in myelination.

Neuron–glia interactions are critical in the nervous system, where they result in the extension of glial pseudopodia. Poitelon et al. isolate these protrusions using an in vitro assay, and, by characterising their proteomes, identify Prohibitin-2 as a regulator of myelination.

Why do we study animal toxins?

Venom (toxins) is an important trait evolved along the evolutionary tree of animals. Our knowledges on venoms, such as their origins and loss, the biological relevance and the coevolutionary patterns with other organisms are greatly helpful in understanding many fundamental biological questions, i.e., the environmental adaptation and survival competition, the evolution shaped development and balance of venoms, and the sophisticated correlations among venom, immunity, body power, intelligence, their genetic basis, inherent association, as well as the cost-benefit and trade-offs of biological economy. Lethal animal envenomation can be found worldwide. However, from foe to friend, toxin studies have led lots of important discoveries and exciting avenues in deciphering and fighting human diseases, including the works awarded the Nobel Prize and lots of key clinic therapeutics. According to our survey, so far, only less than 0.1% of the toxins of the venomous animals in China have been explored. We emphasize on the similarities shared by venom and immune systems, as well as the studies of toxin knowledge-based physiological toxin-like proteins/peptides (TLPs). We propose the natural pairing hypothesis. Evolution links toxins with humans. Our mission is to find out the right natural pairings and interactions of our body elements with toxins, and with endogenous toxin-like molecules. Although, in nature, toxins may endanger human lives, but from a philosophical point of view, knowing them well is an effective way to better understand ourselves. So, this is why we study toxins.

Characterization of Prohibitin 1 as a Host Partner of Vibrio vulnificus RtxA1 Toxin

RtxA1 toxin, which results in cytoskeletal rearrangement, contact cytotoxicity, hemolysis, tissue invasion, and lethality in mice, is the most potent cytotoxic virulence factor of Vibrio vulnificus. Bioinformatics analysis of rtxA1 predicted 4 functional domains that presumably performed discrete functions during host cell killing. V. vulnificus RtxA1 has a unique domain designated as RtxA1-D2, corresponding to amino acids 1951-2574, which is absent in Vibrio cholerae multifunctional-autoprocessing repeats-in-toxin, suggesting that this domain confers specific biological functions to V. vulnificus RtxA1. HeLa cells expressing green fluorescent protein-RtxA1-D2 became round and lost their viability. A yeast 2-hybrid system identified prohibitin (PHB) 1 as the host partner of RtxA1-D2. The specific interaction of RtxA1-D2 with PHB1 was confirmed by performing immunoprecipitation. Interestingly, V. vulnificus RtxA1 up-regulated PHB1 expression on the cytoplasmic membrane of host cells. Extracellular signal-regulated kinase and p38 mitogen-activated protein kinase pathways were confirmed as being important in the up-regulation of PHB1 by using inhibitors. Down-regulation of PHB1 by small interfering RNAs decreased the cytotoxicity of RtxA1-D2 against HeLa cells. The pretreatment of an anti-PHB1 antibody impaired the cytotoxicity of V. vulnificus RtxA1. These results suggest that the involvement PHB1 in the RtxA1 cytotoxicity has significant implications for the pathogenesis of V. vulnificus infections.

Characterization of PHB1 and its role in mitochondrial maturation and yolk platelet degradation during development of Artemia embryos

BACKGROUND

To cope with harsh environments, crustaceans such as Artemia produce diapause gastrula embryos (cysts) with suppressed metabolism. Metabolism and development resume during post-diapause development, but the mechanism behind these cellular events remains largely unknown.

PRINCIPAL FINDING

Our study investigated the role of prohibitin 1 (PHB1) in metabolic reinitiation during post-diapause development. We found that PHB1 was developmentally regulated via changes in phosphorylation status and localization. Results from RNA interference experiments demonstrated PHB1 to be critical for mitochondrial maturation and yolk degradation during development. In addition, PHB1 was present in yolk platelets, and it underwent ubiquitin-mediated degradation during the proteolysis of yolk protein.

CONCLUSIONS/SIGNIFICANCE

PHB1 has an indispensable role in coordinating mitochondrial maturation and yolk platelet degradation during development in Artemia. This novel function of PHB1 provides new clues to comprehend the roles of PHB1 in metabolism and development.

Mast cell-derived serine proteinase regulates T helper 2 polarization

Although mast cells play a critical role in allergic reactions, the cells are also involved in the protective immunity in the body. This study aims to investigate the role of mast cells in immune regulation during aberrant T helper (Th)2 responses. In this study, an adoptive antigen-specific Th2 response model was established with mast cell-deficient mice to test the role of mast cell in the immune regulation. Cell culture was employed to test the role of mast cells in the modulation of the expression of B cell lymphoma 6 protein (Bcl-6) in Th2 cells. The results showed that after adoptive transfer with immune cells, the mast cell-deficient mice showed stronger Th2 pattern responses in the intestine than that in the mast cell-sufficient mice. Mast cell-derived mouse mast cell protease-6 increased the expression of Bcl-6 in Th2 cells. Bcl-6 inhibited the expression of GATA-3 in Th2 cells, subsequently, forkhead box P3 was increased and the Th2 cytokines were reduced in the cells; the cells thus showed the immune regulatory properties similar to regulatory T cells. We conclude that bedsides initiating immune inflammation, mast cells also contribute to the immune regulation on Th2 polarization.