Proprotein convertase 1/3 (PC1/3) in the rat alveolar macrophage cell line NR8383: localization, trafficking and effects on cytokine secretion

From Cell to Symptoms: The Role of SARS-CoV-2 Cytopathic Effects in the Pathogenesis of COVID-19 and Long COVID

Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS-CoV-2) infection triggers various events from molecular to tissue level, which in turn is given by the intrinsic characteristics of each patient. Given the molecular diversity characteristic of each cellular phenotype, the possible cytopathic, tissue and clinical effects are difficult to predict, which determines the heterogeneity of COVID-19 symptoms. The purpose of this article is to provide a comprehensive review of the cytopathic effects of SARS-CoV-2 on various cell types, focusing on the development of COVID-19, which in turn may lead, in some patients, to a persistence of symptoms after recovery from the disease, a condition known as long COVID. We describe the molecular mechanisms underlying virus-host interactions, including alterations in protein expression, intracellular signaling pathways, and immune responses. In particular, the article highlights the potential impact of these cytopathies on cellular function and clinical outcomes, such as immune dysregulation, neuropsychiatric disorders, and organ damage. The article concludes by discussing future directions for research and implications for the management and treatment of COVID-19 and long COVID.

G protein-coupled receptor kinase 6 (GRK6) regulates insulin processing and secretion via effects on proinsulin conversion to insulin

Recent studies identified a missense mutation in the gene coding for G protein–coupled receptor kinase 6 (GRK6) that segregates with type 2 diabetes (T2D). To better understand how GRK6 might be involved in T2D, we used pharmacological inhibition and genetic knockdown in the mouse β-cell line, MIN6, to determine whether GRK6 regulates insulin dynamics. We show inhibition of GRK5 and GRK6 increased insulin secretion but reduced insulin processing while GRK6 knockdown revealed these same processing defects with reduced levels of cellular insulin. GRK6 knockdown cells also had attenuated insulin secretion but enhanced proinsulin secretion consistent with decreased processing. In support of these findings, we demonstrate GRK6 rescue experiments in knockdown cells restored insulin secretion after glucose treatment. The altered insulin profile appears to be caused by changes in the proprotein convertases, the enzymes responsible for proinsulin to insulin conversion, as GRK6 knockdown resulted in significantly reduced convertase expression and activity. To identify how the GRK6-P384S mutation found in T2D patients might affect insulin processing, we performed biochemical and cell biological assays to study the properties of the mutant. We found that while GRK6-P384S was more active than WT GRK6, it displayed a cytosolic distribution in cells compared to the normal plasma membrane localization of GRK6. Additionally, GRK6 overexpression in MIN6 cells enhanced proinsulin processing, while GRK6-P384S expression had little effect. Taken together, our data show that GRK6 regulates insulin processing and secretion in a glucose-dependent manner and provide a foundation for understanding the contribution of GRK6 to T2D.

Therapeutic anti-glioma effect of the combined action of PCSK inhibitor with the anti-tumoral factors secreted by Poly (I:C)-stimulated macrophages

Macrophages plasticity is a key feature in cancer progression. Neoplastic cells can alter their immune functions and orient them into a pro-tumoral phenotype. In this context, we developed a new therapeutic strategy to switch macrophages phenotype and reactivate their anti-tumoral functions. We showed a dual activity of a proprotein convertases inhibitor as anti-glioma drug and anti-tumoral macrophages' reactivation drug. Proprotein convertases are proteases that cleave proteins into functional proteins. Several of their substrates are involved in tumorigenesis and immunosuppression. We combine here proprotein convertases inhibitor with Poly (I:C), a TLR3 ligand, to increase the anti-tumoral activity of macrophages. With mass spectrometry-based proteomics, system biology, combined with biological assays, we established that a stimulation of macrophages with Poly (I:C) increased their secretion of pro-inflammatory cytokines and anti-tumoral factors. 3D invasion assay showed the efficacy of these anti-tumoral factors against mixed glioma cells and macrophages spheroids. Besides, immunofluorescence and proliferation assays showed an additive effect of the proprotein convertases inhibitor and the anti-tumoral factors secreted by Poly (I:C)-treated macrophages on both anti-glioma activity and macrophages anti-tumoral orientation directly in tumor microenvironment, leading to an innovative glioma therapy.

Semysinthetic biflavonoid Morelloflavone-7,4',7″,3‴,4‴-penta-O-butanoyl is a more potent inhibitor of Proprotein Convertases Subtilisin/Kexin PC1/3 than Kex2 and Furin

BACKGROUND

Garcinia brasiliensis is a species native to the Amazon forest. The white mucilaginous pulp is used in folk medicine as a wound healing agent and for peptic ulcer, urinary, and tumor disease treatments. The activity of the proprotein convertases (PCs) Subtilisin/Kex is associated with the development of viral, bacterial and fungal infections, osteoporosis, hyperglycemia, atherosclerosis, cardiovascular, neurodegenerative and neoplastic diseases.

METHODS

Morelloflavone (BF1) and semisynthetic biflavonoid (BF2, 3 and 4) from Garcinia brasiliensis were tested as inhibitor of PCs Kex2, PC1/3 and Furin, and determined IC₅₀, K_i, human proinflammatory cytokines secretion in Caco-2 cells, mechanism of inhibition, and performed molecular docking studies.

RESULTS

Biflavonoids were more effective in the inhibition of neuroendocrine PC1/3 than mammalian Furin and fungal Kex2. BF1 presented a mixed inhibition mechanism for Kex2 and PC1, and competitive inhibition for Furin. BF4 has no good interaction with Kex2 and Furin since carboxypropyl groups results in steric hindrance to ligand-protein interactions. Carboxypropyl groups of BF4 promote steric hindrance with Kex2 and Furin, but effective in the affinity of PC1/3. BF4 was more efficient at inhibiting PCl/3 (IC₅₀ = 1.13 μM and K_i = 0,59 μM, simple linear competitive mechanism of inhibition) than Kex2, Furin. Also, our results strongly suggested that BF4 also inhibits the endogenous cellular PC1/3 activity in Caco-2 cells, since PC1/3 inhibition by BF4 causes a large increase in IL-8 and IL-1β secretion in Caco-2 cells.

CONCLUSIONS

BF4 is a potent and selective inhibitor of PC1/3.

GENERAL SIGNIFICANCE

BF4 is the best candidate for further clinical studies on inhibition of PC1/3.

Immune mediating molecules and pathogenesis of COVID-19-associated neurological disease

Background

Long period of SARS-CoV-2 infection has been associated with psychiatric and cognitive disorders in adolescents and children. SARS-CoV-2 remains dormant in the CNS leading to neurological complications. The wide expression of ACE2 in the brain raises concern for its involvement in SARS-CoV-2 infection. Though, the mechanistic insights about blood-brain barriers (BBB) crossing by SARS-CoV-2 and further brain infection are still not clear. Moreover, the mechanism behind dormant SARS-CoV-2 infections leading to chronic neurological disorders needs to be unveiled. There is an urgent need to find out the risk factor involved in COVID-19-associated neurological disease. Therefore, the role of immune-associated genes in the pathogenesis of COVID-19 associated neurological diseases is presented which could contribute to finding associated genetic risk factors.

Method

The search utilizing multiple databases, specifically, EMBASE, PubMed (Medline), and Google Scholar was performed. Moreover, the literature survey on the involvement of COVID-19, neuropathogenesis, and its consequences was done.

Description

Persistent inflammatory stimuli may promote the progression of neurodegenerative diseases. An increased expression level of cytokine, chemokine, and decreased expression level of immune cells has been associated with the COVID-19 patient. Cytokine storm was observed in severe COVID-19 patients. The nature of SARS-CoV-2 infection can be neuroinflammatory. Genes of immune response could be associated with neurodegenerative diseases.

Conclusion

The present review will provide a useful framework and help in understanding COVID-19-associated neuropathogenesis. Experimental studies on immune-associated genes in COVID-19 patients with neurological manifestations could be helpful to establish its neuropathogenesis.

The Role of Proprotein Convertases in the Regulation of the Function of Immune Cells in the Oncoimmune Response

Proprotein convertases (PC) are a family of 9 serine proteases involved in the processing of cellular pro-proteins. They trigger the activation, inactivation or functional changes of many hormones, neuropeptides, growth factors and receptors. Therefore, these enzymes are essential for cellular homeostasis in health and disease. Nine PC subtilisin/kexin genes (PCSK1 to PCSK9) encoding for PC1/3, PC2, furin, PC4, PC5/6, PACE4, PC7, SKI-1/S1P and PCSK9 are known. The expression of PC1/3, PC2, PC5/6, Furin and PC7 in lymphoid organs such as lymph nodes, thymus and spleen has suggested a role for these enzymes in immunity. In fact, knock-out of Furin in T cells was associated with high secretion of pro-inflammatory cytokines and autoantibody production in mice. This suggested a key role for this enzyme in immune tolerance. Moreover, Furin through its proteolytic activity, regulates the suppressive functions of Treg and thus prevents chronic inflammation and autoimmune diseases. In macrophages, Furin is also involved in the regulation of their inflammatory phenotype. Similarly, PC1/3 inhibition combined with TLR4 stimulation triggers the activation of the NF-κB signaling pathway with an increased secretion of pro-inflammatory cytokines. Factors secreted by PC1/3 KD macrophages stimulated with LPS exert a chemoattractive effect on naive auxiliary T lymphocytes (Th0) and anti-tumoral activities. The link between TLR and PCs is thus very important in inflammatory response regulation. Furin regulates TL7 and TLR8 processing and trafficking whereas PC1/3 controls TLR4 and TLR9 trafficking. Since PC1/3 and Furin are key regulators of both the innate and adaptive immune responses their inhibition may play a major role in oncoimmune therapy. The role of PCs in the oncoimmune response and therapeutic strategies based on PCs inhibition are proposed in the present review.

Epigenetic Studies Revealed a Ghost Proteome in PC1/3 KD Macrophages under Antitumoral Resistance Induced by IL-10

Our previous investigation on macrophages has allowed us to show that the inhibition of the enzyme proprotein convertase (PC1/3) controls the activation of macrophages. We demonstrated that PC1/3 knockdown (KD) in macrophages exhibits an increased secretion of proinflammatory and antitumoral factors. In this biological context, we assessed the presence of histone modifications and the presence and contribution of a "ghost proteome" in these macrophages. We identified a set of alternative proteins (AltProts) that have a key role in the regulation of various signaling pathways. In this study, to further investigate the underlying mechanisms involved in the resistance of PC1/3-KD macrophages to anti-inflammatory stimuli, we have conducted a proteomic system biology study to assess the epigenome variation, focusing on histone modifications. Results from our study have indicated the presence of significant variations in histone modifications along with the identification of 28 AltProts, which can be correlated with antitumoral resistance under IL-10 stimulation. These findings highlight a key role of altered epigenome histone modifications in driving resistance and indicate that like the reference proteins, AltProts can have a major impact in the field of epigenetics and regulation of gene expression, as shown in our results.

The Lung Macrophage in SARS-CoV-2 Infection: A Friend or a Foe?

Respiratory, circulatory, and renal failure are among the gravest features of COVID-19 and are associated with a very high mortality rate. A common denominator of all affected organs is the expression of angiotensin-converting enzyme 2 (ACE2), a protease responsible for the conversion of Angiotensin 1-8 (Ang II) to Angiotensin 1-7 (Ang 1-7). Ang 1-7 acts on these tissues and in other target organs via Mas receptor (MasR), where it exerts beneficial effects, including vasodilation and suppression of inflammation and fibrosis, along an attenuation of cardiac and vascular remodeling. Unfortunately, ACE2 also serves as the binding receptor of SARS viral spike glycoprotein, enabling its attachment to host cells, with subsequent viral internalization and replication. Although numerous reports have linked the devastating organ injuries to viral homing and attachment to organ-specific cells widely expressing ACE2, little attention has been given to ACE-2 expressed by the immune system. Herein we outline potential adverse effects of SARS-CoV2 on macrophages and dendritic cells, key cells of the immune system expressing ACE2. Specifically, we propose a new hypothesis that, while macrophages play an important role in antiviral defense mechanisms, in the case of SARS-CoV, they may also serve as a Trojan horse, enabling viral anchoring specifically within the pulmonary parenchyma. It is tempting to assume that diverse expression of ACE2 in macrophages among individuals might govern the severity of SARS-CoV-2 infection. Moreover, reallocation of viral-containing macrophages migrating out of the lung to other tissues is theoretically plausible in the context of viral spread with the involvement of other organs.

The Role of a Proprotein Convertase Inhibitor in Reactivation of Tumor-Associated Macrophages and Inhibition of Glioma Growth

Tumors are characterized by the presence of malignant and non-malignant cells, such as immune cells including macrophages, which are preponderant. Macrophages impact the efficacy of chemotherapy and may lead to drug resistance. In this context and based on our previous work, we investigated the ability to reactivate macrophages by using a proprotein convertases inhibitor. Proprotein convertases process immature proteins into functional proteins, with several of them having a role in immune cell activation and tumorigenesis. Macrophages were treated with a peptidomimetic inhibitor targeting furin, PC1/3, PC4, PACE4, and PC5/6. Their anti-glioma activity was analyzed by mass spectrometry-based proteomics and viability assays in 2D and 3D in vitro cultures. Comparison with temozolomide, the drug used for glioma therapy, established that the inhibitor was more efficient for the reduction of cancer cell density. The inhibitor was also able to reactivate macrophages through the secretion of several immune factors with antitumor properties. Moreover, two proteins considered as good glioma patient survival indicators were also identified in 3D cultures treated with the inhibitor. Finally, we established that the proprotein convertases inhibitor has a dual role as an anti-glioma drug and anti-tumoral macrophage reactivation drug. This strategy could be used together with chemotherapy to increase therapy efficacy in glioma.

PC1/3 KD Macrophages Exhibit Resistance to the Inhibitory Effect of IL-10 and a Higher TLR4 Activation Rate, Leading to an Anti-Tumoral Phenotype

During tumorigenesis, macrophages are recruited by tumors and orientated towards a pro-tumoral phenotype. One of the main anti-tumoral immunotherapy consists of their re-polarization in an anti-tumoral phenotype. We have demonstrated that the inhibition of proprotein convertase 1/3 combined with TLR4 activation in macrophages is a promising strategy. These macrophages display pro-inflammatory and anti-tumoral phenotypes. A hallmark is a stronger activation of the pro-inflammatory NFKB pathway. We believe that this can be explained by a modification of TLR4 expression at the cell surface or MYD88 cleavage since it exhibits a potential cleavage site for proprotein convertases. We tested these hypotheses through immunofluorescence and Western blot experiments. A proteomics study was also performed to test the sensitivity of these macrophages to IL-10. We demonstrated that these macrophages treated with LPS showed a quicker re-expression of TLR4 at the cell surface. The level of MYD88 was also higher when TLR4 was internalized. Moreover, these macrophages were resistant to the pro-tumoral effect of IL-10 and still produced pro-inflammatory factors. This established that the sensitivity to anti-inflammatory molecules and the length of TLR4 desensitization were reduced in these macrophages. Therefore, during antitumoral immunotherapy, a repeated stimulation of TLR4 may reactivate PC1/3 inhibited macrophages even in an anti-inflammatory environment.

Water-assisted laser desorption/ionization mass spectrometry for minimally invasive in vivo and real-time surface analysis using SpiderMass

Rapid, sensitive, precise and accurate analysis of samples in their native in vivo environment is critical to better decipher physiological and physiopathological mechanisms. SpiderMass is an ambient mass spectrometry (MS) system designed for mobile in vivo and real-time surface analyses of biological tissues. The system uses a fibered laser, which is tuned to excite the most intense vibrational band of water, resulting in a process termed water-assisted laser desorption/ionization (WALDI). The water molecules act as an endogenous matrix in a matrix-assisted laser desorption ionization (MALDI)-like scenario, leading to the desorption/ionization of biomolecules (lipids, metabolites and proteins). The ejected material is transferred to the mass spectrometer through an atmospheric interface and a transfer line that is several meters long. Here, we formulate a three-stage procedure that includes (i) a laser system setup coupled to a Waters Q-TOF or Thermo Fisher Q Exactive mass analyzer, (ii) analysis of specimens and (iii) data processing. We also describe the optimal setup for the analysis of cell cultures, fresh-frozen tissue sections and in vivo experiments on skin. With proper optimization, the system can be used for a variety of different targets and applications. The entire procedure takes 1-2 d for complex samples.

Deciphering molecular consequences of the proprotein convertase 1/3 inhibition in macrophages for application in anti-tumour immunotherapy

During tumour development, macrophages are recruited to the tumour site and orientated towards an anti-inflammatory phenotype. Due to their immunosuppressive function, tumour associated macrophages (TAMs) are recognized as major components in tumour progression. Changing these macrophages to a pro-inflammatory phenotype is thus extensively studied as a potential means for developing novel anti-tumour therapy. In this context, we found that the Proprotein convertase 1/3 (PC1/3) is a relevant target. Proteomic analysis reveals that PC1/3 knockdown (KD) macrophages present all the characteristic of activated pro-inflammatory macrophages. Moreover, in PC1/3 KD macrophages, TLR4 and TLR9 signaling pathways can be enhanced leading to the secretion of pro-inflammatory factors and anti-tumour factors. To develop an efficient anti-tumour immunotherapy, we may (i) target TAMs directly inside the tumour site for PC1/3 inhibition and TLR activation and used them as "Trojan macrophages" or (ii) directly take advantage of PC1/3 inhibited macrophages and use them as "drone macrophages" by activating them "at distance" with a TLR ligand. Therefore, PC1/3 inhibited macrophages constitute an innovative cell therapy to treat tumours efficiently.

Paclitaxel Treatment and Proprotein Convertase 1/3 (PC1/3) Knockdown in Macrophages is a Promising Antiglioma Strategy as Revealed by Proteomics and Cytotoxicity Studies

High grade gliomas are the most common brain tumors in adult. These tumors are characterized by a high infiltration in microglial cells and macrophages. The immunosuppressive tumor environment is known to orient immune cells toward a pro-tumoral and anti-inflammatory phenotype. Therefore, the current challenge for cancer therapy is to find a way to reorient macrophages toward an antitumoral phenotype. Previously, we demonstrated that macrophages secreted antitumoral factors when they were invalidated for the proprotein converstase 1/3 (PC1/3) and treated with LPS. However, achieving an activation of macrophages via LPS/TLR4/Myd88-dependent pathway appears yet unfeasible in cancer patients. On the contrary, the antitumor drug Paclitaxel is also known to activate the TLR4 MyD88-dependent signaling pathway and mimics LPS action. Therefore, we evaluated if PC1/3 knock-down (KD) macrophages could be activated by Paclitaxel and efficient against glioma. We report here that such a treatment of PC1/3 KD macrophages drove to the overexpression of proteins mainly involved in cytoskeleton rearrangement. In support of this finding, we found that these cells exhibited a Ca²⁺ increase after Paclitaxel treatment. This is indicative of a possible depolymerization of microtubules and may therefore reflect an activation of inflammatory pathways in macrophages. In such a way, we found that PC1/3 KD macrophages displayed a repression of the anti-inflammatory pathway STAT3 and secreted more pro-inflammatory cytokines. Extracellular vesicles isolated from these PC1/3 KD cells inhibited glioma growth. Finally, the supernatant collected from the coculture between glioma cells and PC1/3 KD macrophages contained more antitumoral factors. These findings unravel the potential value of a new therapeutic strategy combining Paclitaxel and PC1/3 inhibition to switch macrophages toward an antitumoral immunophenotype.

Brain-Cortex Microglia-Derived Exosomes: Nanoparticles for Glioma Therapy

The function and integrity of the nervous system require interactive exchanges among neurons and glial cells. Exosomes and other extracellular vesicles (EVs) are emerging as a key mediator of intercellular communication, capable of transferring nucleic acids, proteins and lipids influencing numerous functional and pathological aspects of both donor and recipient cells. The immune response mediated by microglia-derived exosomes is most prominently involved in the spread of neuroinflammation, neurodegenerative disorders, and brain cancer. Therefore, in the present study we describe a reproducible and highly efficient method for yielding purified primary microglia cells, followed by exosome isolation and their characterization. An in vitro biological assay demonstrates that microglia-derived exosomes tested on a 3D spheroid glioma culture were able to inhibit tumor invasion in time course. These results evidence that brain microglia-derived exosomes could be used as nanotherapeutic agents against glioma cells.

Proprotein convertase 1/3 inhibited macrophages: A novel therapeutic based on drone macrophages

We demonstrated here thanks to proteomic, that proprotein convertase 1/3 knockdown macrophages present all the characteristic of activated pro-inflammatory macrophages. TLR4 and TLR9 signaling pathways can be enhanced leading to the secretion of pro-inflammatory factors and antitumor factors. We can control their activation by controlling one enzyme, PC1/3. In a tumor context, PC1/3 inhibition in macrophages may reactivate them and lead to a cytokine storm after stimulation "at distance" with a TLR ligand. Therefore, we name these proprotein convertase inhibited macrophages the "drone macrophages". They constitute an innovative cell therapy to treat efficiently tumors.

The proprotein convertase PC1/3 regulates TLR9 trafficking and the associated signaling pathways

Endosomal TLR9 is considered as a potent anti-tumoral therapeutic target. Therefore, it is crucial to decipher the mechanisms controlling its trafficking since it determines TLR9 activation and signalling. At present, the scarcity of molecular information regarding the control of this trafficking and signalling is noticeable. We have recently demonstrated that in macrophages, proprotein convertase 1/3 (PC1/3) is a key regulator of TLR4 Myd88-dependent signalling. In the present study, we established that PC1/3 also regulates the endosomal TLR9. Under CpG-ODN challenge, we found that PC1/3 traffics rapidly to co-localize with TLR9 in CpG-ODN-containing endosomes with acidic pH. In PC1/3 knockdown macrophages, compartmentalization of TLR9 was altered and TLR9 clustered in multivesicular bodies (MVB) as demonstrated by co-localization with Rab7. This demonstrates that PC1/3 controls TLR9 trafficking. This clustering of TLR9 in MVB dampened the anti-inflammatory STAT3 signalling pathway while it promoted the pro-inflammatory NF-kB pathway. As a result, macrophages from PC1/3 KO mice and rat PC1/3-KD NR8383 macrophages secreted more pro-inflammatory cytokines such as TNF-α, IL6, IL1α and CXCL2. This is indicative of a M1 pro-inflammatory phenotype. Therefore, PC1/3 KD macrophages represent a relevant mean for cell therapy as “Trojan” macrophages.

Molecular Consequences of Proprotein Convertase 1/3 (PC1/3) Inhibition in Macrophages for Application to Cancer Immunotherapy: A Proteomic Study

Macrophages provide the first line of host immune defense. Their activation triggers the secretion of pro-inflammatory cytokines and chemokines recruiting other immune cells. In cancer, macrophages present an M2 anti-inflammatory phenotype promoting tumor growth. In this way, strategies need to be develop to reactivate macrophages. Previously thought to be expressed only in cells with a neural/neuroendocrine phenotype, the proprotein convertase 1/3 has been shown to also be expressed in macrophages and regulated as a function of the Toll-like receptor immune response. Here, we investigated the intracellular impact of the down-regulation of the proprotein convertase 1/3 in NR8383 macrophages and confirmed the results on macrophages from PC1/3 deficient mice. A complete proteomic study of secretomes and intracellular proteins was undertaken and revealed that inhibition of proprotein convertase 1/3 orient macrophages toward an M1 activated phenotype. This phenotype is characterized by filopodial extensions, Toll-like receptor 4 MyD88-dependent signaling, calcium entry augmentation and the secretion of pro-inflammatory factors. In response to endotoxin/lipopolysaccharide, these intracellular modifications increased, and the secreted factors attracted naïve T helper lymphocytes to promote the cytotoxic response. Importantly, the application of these factors onto breast and ovarian cancer cells resulted in a decrease viability or resistance. Under inhibitory conditions using interleukin 10, PC1/3-knockdown macrophages continued to secrete inflammatory factors. These data indicate that targeted inhibition of proprotein convertase 1/3 could represent a novel type of immune therapy to reactivate intra-tumoral macrophages.