Plant-Produced Asialo-Erythropoietin Restores Pancreatic Beta-Cell Function by Suppressing Mammalian Sterile-20-like Kinase (MST1) and Caspase-3 Activation

Mechanism and therapeutic potential of hippo signaling pathway in type 2 diabetes and its complications

Loss of pancreatic islet cell mass and function is one of the most important factors in the development of type 2 diabetes mellitus, and hyperglycemia-induced lesions in other organs are also associated with apoptosis or hyperproliferation of the corresponding tissue cells. The Hippo signaling pathway is a key signal in the regulation of cell growth, proliferation and apoptosis, which has been shown to play an important role in the regulation of diabetes mellitus and its complications. Excessive activation of the Hippo signaling pathway under high glucose conditions triggered apoptosis and decreased insulin secretion in pancreatic islet cells, while dysregulation of the Hippo signaling pathway in the cells of other organ tissues led to proliferation or apoptosis and promoted tissue fibrosis, which aggravated the progression of diabetes mellitus and its complications. This article reviews the mechanisms of Hippo signaling, its individual and reciprocal regulation in diabetic pancreatic pathology, and its emerging role in the pathophysiology of diabetic complications. Potential therapeutics for diabetes mellitus that have been shown to target the Hippo signaling pathway are also summarized to provide information for the clinical management of type 2 diabetes mellitus.

GLDC promotes colorectal cancer metastasis through epithelial-mesenchymal transition mediated by Hippo signaling pathway

Cancer metastasis remains a major cause of death in cancer patients, and epithelial-mesenchymal transition (EMT) plays a decisive role in cancer metastasis. Recently, abnormal expression of Glycine Decarboxylase (GLDC) has been demonstrated in tumor progression, and GLDC is up-regulated in cancers, such as lung, prostate, bladder, and cervical cancers. However, the exact role of GLDC in colorectal cancer (CRC) progression remains to be elucidated. The aim of our study was to explore the role of GLDC in CRC metastasis. The GSE75117 database was used to investigate GLDC expression in tumor center and invasive front tissues and we found that GLDC expression levels were higher in the invasive front tissue. GLDC expression levels were negatively correlated with the prognosis of CRC patients. In vitro studies have showed that GLDC can promote invasion and migration of CRC cells by inhibiting the Hippo signaling pathway and regulating the EMT process. Blocking the Hippo signaling pathway with Verteporfin reduced the effect of GLDC on CRC metastasis. In vivo metastasis assays further confirmed that tail vein injection of GLDC+/+ cells induced more lung metastasis, compared to normal CRC cells. The results of this study suggest that GLDC promotes EMT through the Hippo signaling pathway, providing a new therapeutic target for CRC metastasis.

The hippo kinases MST1/2 in cardiovascular and metabolic diseases: A promising therapeutic target option for pharmacotherapy

Cardiovascular diseases (CVDs) and metabolic disorders are major components of noncommunicable diseases, causing an enormous health and economic burden worldwide. There are common risk factors and developmental mechanisms among them, indicating the far-reaching significance in exploring the corresponding therapeutic targets. MST1/2 kinases are well-established proapoptotic effectors that also bidirectionally regulate autophagic activity. Recent studies have demonstrated that MST1/2 influence the outcome of cardiovascular and metabolic diseases by regulating immune inflammation. In addition, drug development against them is in full swing. In this review, we mainly describe the roles and mechanisms of MST1/2 in apoptosis and autophagy in cardiovascular and metabolic events as well as emphasis on the existing evidence for their involvement in immune inflammation. Moreover, we summarize the latest progress of pharmacotherapy targeting MST1/2 and propose a new mode of drug combination therapy, which may be beneficial to seek more effective strategies to prevent and treat CVDs and metabolic disorders.

Cadmium inhibits signal transducer and activator of transcription 6 leading to pancreatic β cell apoptosis

The toxic heavy metal cadmium has been proven to cause pancreatic dysfunction and lead to the development of DM. However, the underlying mechanisms have not been completely elucidated. Here, we investigated the effects of cadmium on the pancreatic β cell line MIN6 and explored the underlying mechanisms. The Cell Counting Kit-8 (CCK8) assay and flow cytometry were used to determine cell viability and apoptosis in MIN6 cells. The expression levels of signal transducer and activator of transcription 6 (STAT6) were assessed by western blotting. We further assessed the effects of cadmium on the function of pancreatic β cells under high glucose levels using enzyme-linked immunosorbent assay (ELISA) and western blotting. Insulin secretion and expression were decreased by cadmium in MIN6 cells. In addition, cadmium suppressed cell viability and promoted apoptosis of MIN6 cells, downregulated insulin secretion and genesis of MIN6 cells under high glucose conditions, while inhibiting STAT6. Furthermore, after treatment with IL-4, the activator of STAT6, the MIN6 cell viability suppression and apoptosis promotion effect caused by cadmium were blocked. In conclusion, cadmium inhibits pancreatic β cell MIN6 growth by regulating the activation of STAT6. Our findings reveal a new mechanism of cadmium toxicity in pancreatic β cells.

Apoptosis in Type 2 Diabetes: Can It Be Prevented? Hippo Pathway Prospects

Diabetes mellitus is a heterogeneous disease of complex etiology and pathogenesis. Hyperglycemia leads to many serious complications, but also directly initiates the process of β cell apoptosis. A potential strategy for the preservation of pancreatic β cells in diabetes may be to inhibit the implementation of pro-apoptotic pathways or to enhance the action of pancreatic protective factors. The Hippo signaling pathway is proposed and selected as a target to manipulate the activity of its core proteins in therapy-basic research. MST1 and LATS2, as major upstream signaling kinases of the Hippo pathway, are considered as target candidates for pharmacologically induced tissue regeneration and inhibition of apoptosis. Manipulating the activity of components of the Hippo pathway offers a wide range of possibilities, and thus is a potential tool in the treatment of diabetes and the regeneration of β cells. Therefore, it is important to fully understand the processes involved in apoptosis in diabetic states and completely characterize the role of this pathway in diabetes. Therapy consisting of slowing down or stopping the mechanisms of apoptosis may be an important direction of diabetes treatment in the future.

Erythropoietin, as a biological macromolecule in modification of tissue engineered constructs: A review

In recent years, tissue engineering has emerged as a promising approach to address limitations of organ transplantation. The ultimate goal of tissue engineering is to provide scaffolds that closely mimic the physicochemical and biological cues of native tissues' extracellular matrix. In this endeavor, new generation of scaffolds have been designed that utilize the incorporation of signaling molecules in order to improve cell recruitment, enhance angiogenesis, exert healing activities, and increase the engraftment of the scaffolds. Among different signaling molecules, the role of erythropoietin (EPO) in regenerative medicine is increasingly being appreciated. It is a biological macromolecule which can prevent programed cell death, modulate inflammation, induce cell proliferation, and provide tissue protection in different disease models. In this review, we have outlined and critically analyzed different techniques of scaffolds' modification with EPO or EPO-loaded nanoparticles. We have also explored different strategies for the incorporation of EPO into scaffolds. Non-hematopoietic functions of EPO have also been discussed. Finalizing with detailed discussion surrounding the applications, challenges, and future perspectives of EPO-modified scaffolds in regenerative medicine.

A Novel Plant-Produced Asialo-rhuEPO Protects Brain from Ischemic Damage Without Erythropoietic Action

Mammalian cell-produced recombinant human erythropoietin (rhuEPO^M) has been shown to be a multimodal neuroprotectant targeting an array of key pathological mechanisms in experimental stroke models. However, the rhuEPO^M clinical trials were terminated due to increased risk of thrombosis, largely ascribed to its erythropoietic function. We recently took advantage of a plant-based expression system lacking sialylation capacity to produce asialo-rhuEPO^P, a rhuEPO derivative without sialic acid residues. In the present study, we proved that asialo-rhuEPO^P is non-erythropoietic by repeated intravenous injection (44 μg/kg bw) in mice showing no increase in hemoglobin levels and red blood cell counts, and confirmed that it is non-immunogenic by measuring humoral response after immunizing the mice. We demonstrate that it is neuroprotective in a cerebral ischemia and reperfusion (I/R) mouse model, exhibiting ~ 50% reduction in cerebral infarct volume and edema, and significant improvement in neurological deficits and histopathological outcome. Our studies further revealed that asialo-rhuEPO^P, like rhuEPO^M, displays pleiotropic neuroprotective effects, including restoring I/R-interrupted mitochondrial fission and fusion proteins, preventing I/R injury-induced increase in mitophagy and autophagy markers, and inhibiting apoptosis to benefit nerve cell survival. Most importantly, asialo-rhuEPO^P lacking erythropoietic activity and immunogenicity holds great translational potential as a multimodal neuroprotectant for stroke treatment.

Glycoengineering tobacco plants to stably express recombinant human erythropoietin with different N-glycan profiles

Plant-based expression system has many potential advantages to produce biopharmaceuticals, but plants cannot be directly used to express human glycoproteins because of their differences in glycosylation abilities from mammals. To exploit plant-based expression system for producing recombinant human erythropoietin (rhuEPO), we glycoengineered tobacco plants by stably introducing seven to eight mammalian genes including a target human EPO into tobacco in order to generate capacities for β1,4-galactosylation, bisecting N-acetylglucosamine (GlcNAc) and sialylation. Wild type human β1,4-galactosyltransferase gene (GalT) or a chimeric GalT gene (ST/GalT) was co-expressed to produce rhuEPO bearing β1,4-galactose-extended N-glycan chains as well as compare their β1,4-galactosylation efficiencies. Five mammalian genes encoding enzymes/transporter for sialic acid biosynthesis, transport and transfer were co-expressed to build sialylation capacity in plants. The human MGAT3 was co-expressed to produce N-glycan chains with bisecting GlcNAc. Our results demonstrated that the above transgenes were incorporated into tobacco genome and transcribed. ST/GalT was found to be more efficient than GalT for β1,4-galactosylation. Furthermore, co-expressing MGAT3 generated N-glycans likely bearing bisected GlcNAc. However, our current efforts did not result in generating sialylation capacity. Created transgenic plants expressing EPO and ST/GalT could be used to produce rhuEPO with high proportion of β1,4-galactose-extended N-glycan chains for tissue protective purposes.

The MEK-ERK-MST1 Axis Potentiates the Activation of the Extrinsic Apoptotic Pathway during GDC-0941 Treatment in Jurkat T Cells

The discrete activation of individual caspases is essential during T-cell development, activation, and apoptosis. Humans carrying nonfunctional caspase-8 and caspase-8 conditional knockout mice exhibit several defects in the progression of naive CD4⁺ T cells to the effector stage. MST1, a key kinase of the Hippo signaling pathway, is often presented as a substrate of caspases, and its cleavage by caspases potentiates its activity. Several studies have focused on the involvement of MST1 in caspase activation and also reported several defects in the immune system function caused by MST1 deficiency. Here, we show the rapid activation of the MEK-ERK-MST1 axis together with the cleavage and activation of caspase-3, -6, -7, -8, and -9 after PI3K signaling blockade by the selective inhibitor GDC-0941 in Jurkat T cells. We determined the phosphorylation pattern of MST1 using a phosphoproteomic approach and identified two amino acid residues phosphorylated in an ERK-dependent manner after GDC-0941 treatment together with a novel phosphorylation site at S21 residue, which was extensively phosphorylated in an ERK-independent manner during PI3K signaling blockade. Using caspase inhibitors and the inhibition of MST1 expression using siRNA, we identified an exclusive role of the MEK-ERK-MST1 axis in the activation of initiator caspase-8, which in turn activates executive caspase-3/-7 that finally potentiate MST1 proteolytic cleavage. This mechanism forms a positive feed-back loop that amplifies the activation of MST1 together with apoptotic response in Jurkat T cells during PI3K inhibition. Altogether, we propose a novel MEK-ERK-MST1-CASP8-CASP3/7 apoptotic pathway in Jurkat T cells and believe that the regulation of this pathway can open novel possibilities in systemic and cancer therapies.

Recombinant asialoerythropoetin protects HL-1 cardiomyocytes from injury via suppression of Mst1 activation

Background

Recombinant human erythropoietin (rhuEPO) and asialoerythropoietin (asialo-rhuEPO) are cardioprotective. However, the protective effects of rhuEPO could not be translated into clinical practice because of its hematopoiesis-associated side effects while non-erythropoietic asialo-rhuEPO is unavailable in large quantities for clinical studies. This study was designed to investigate the cardiomyocyte protective potential of plant-produced asialo-rhuEPO (asialo-rhuEPO^P) against staurosporine (STS)-induced injury in HL-1 murine cardiomyocytes and identify cellular pathway(s) responsible for its cardioprotection.

Methods

HL-1 cardiomyocytes were simultaneously treated with STS and asialo-rhuEPO^P. Cellular injury, apoptosis, and cell viabilities were measured by LDH assay, Hoechst staining and trypan blue exclusion method, respectively while western blotting was used to study its effects on apoptosis and autophagy hallmarks.

Results

Our results showed that 20 IU/ml asialo-rhuEPO^P provided 39% protection to cardiomyocytes compared to STS-treated cells, which is 2-fold better than that of mammalian cell-produce rhuEPO (rhuEPO^M). Asialo-rhuEPO^P was found to suppress activation of proapoptotic kinase Mst1 (mammalian Sterile-20-like kinase 1) and FOXO3, leading to inhibition of apoptotic pathway and restoration of autophagy as indicated by the reduction of fragmented/condensed nuclei, altered ratios of Bax/Bcl2, p-Bad/Bad, cytosol/mitochondrial cyt c and caspase-3 activation, and the restored levels of autophagy markers Beclin1, p62 and LC3B-II. Additionally, Akt was found to be activated and FOXO3 was phosphorylated on Ser253, suggesting inhibition of FOXO3 transcriptional function.

Conclusions

Asialo-rhuEPO^P-mediated cardioprotection occurs through activation of PI3K/Akt pathway leading to suppression of Mst1 activation and promoting cardiomyocyte survival.

General significance

Asialo-rhuEPO^P could be used to modulate Mst1 activity elevated under numerous pathological states.

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Recombinant asialo-rhuEPO protect HL-1 cardiomyocytes against STS-induced injury.

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Protective effect of recombinant asialo-rhuEPO is superior to sialylated EPO.

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Asialo-rhuEPO suppresses activation of proapoptotic kinase MSt1 by activating Akt.

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Asialo-rhuEPO restores autophagy and inhibits apoptosis to promote cell survival.

Hippo Signaling: Key Emerging Pathway in Cellular and Whole-Body Metabolism

The evolutionarily conserved Hippo pathway is a key regulator of organ size and tissue homeostasis. Its dysregulation is linked to multiple pathological disorders. In addition to regulating development and growth, recent studies show that Hippo pathway components such as MST1/2 and LATS1/2 kinases, as well as YAP/TAZ transcriptional coactivators, are regulated by metabolic pathways and that the Hippo pathway controls metabolic processes at the cellular and organismal levels in physiological and metabolic disease states such as obesity, type 2 diabetes (T2D), nonalcoholic fatty liver disease (NAFLD), cardiovascular disorders, and cancer. In this review we summarize the connection between key Hippo components and metabolism, and how this interplay regulates cellular metabolism and metabolic pathways. The emerging function of Hippo in the regulation of metabolic homeostasis under physiological and pathological conditions is highlighted.

mTORC2 Signaling: A Path for Pancreatic β Cell's Growth and Function

The mechanistic target of rapamycin (mTOR) signaling pathway is an evolutionary conserved pathway that senses signals from nutrients and growth factors to regulate cell growth, metabolism and survival. mTOR acts in two biochemically and functionally distinct complexes, mTOR complex 1 (mTORC1) and 2 (mTORC2), which differ in terms of regulatory mechanisms, substrate specificity and functional outputs. While mTORC1 signaling has been extensively studied in islet/β-cell biology, recent findings demonstrate a distinct role for mTORC2 in the regulation of pancreatic β-cell function and mass. mTORC2, a key component of the growth factor receptor signaling, is declined in β cells under diabetogenic conditions and in pancreatic islets from patients with type 2 diabetes. β cell-selective mTORC2 inactivation leads to glucose intolerance and acceleration of diabetes as a result of reduced β-cell mass, proliferation and impaired glucose-stimulated insulin secretion. Thereby, many mTORC2 targets, such as AKT, PKC, FOXO1, MST1 and cell cycle regulators, play an important role in β-cell survival and function. This indicates mTORC2 as important pathway for the maintenance of β-cell homeostasis, particularly to sustain proper β-cell compensatory response in the presence of nutrient overload and metabolic demand. This review summarizes recent emerging advances on the contribution of mTORC2 and its associated signaling on the regulation of glucose metabolism and functional β-cell mass under physiological and pathophysiological conditions in type 2 diabetes.