The MST3/STK24 kinase mediates impaired fasting blood glucose after a high-fat diet

GCKIII kinases control hepatocellular lipid homeostasis via shared mode of action

Metabolic dysfunction-associated steatotic liver disease has emerged as a leading global cause of chronic liver disease. Our recent translational investigations have shown that the STE20-type kinases comprising the GCKIII subfamily-MST3, STK25, and MST4-associate with hepatic lipid droplets and regulate ectopic fat storage in the liver; however, the mode of action of these proteins remains to be resolved. By comparing different combinations of the silencing of MST3, STK25, and/or MST4 in immortalized human hepatocytes, we found that their single knockdown results in a similar reduction in hepatocellular lipid content and metabolic stress, without any additive or synergistic effects observed when all three kinases are simultaneously depleted. A genome-wide yeast two-hybrid screen of the human hepatocyte library identified several interaction partners contributing to the GCKIII-mediated regulation of liver lipid homeostasis, that is, PDCD10 that protects MST3, STK25, and MST4 from degradation, MAP4K4 that regulates their activity via phosphorylation, and HSD17B11 that controls their action via a conformational change. Finally, using in vitro kinase assays on microfluidic microarrays, we pinpointed various downstream targets that are phosphorylated by the GCKIII kinases, with known functions in lipogenesis, lipolysis, and lipid secretion, as well as glucose uptake, glycolysis, hexosamine synthesis, and ubiquitination. Together, this study demonstrates that the members of the GCKIII kinase subfamily regulate hepatocyte lipid metabolism via common pathways. The results shed new light on the role of MST3, STK25, and MST4, as well as their interactions with PDCD10, MAP4K4, and HSD17B11, in the control of liver lipid homeostasis and metabolic dysfunction-associated steatotic liver disease susceptibility.

7-Hydroxyflavone improves nonalcoholic fatty liver disease by acting on STK24

The escalating incidence of nonalcoholic fatty liver disease (NAFLD) is closely associated with a high-fat diet, leading to a decline in quality of life and significant health impairment. 7-Hydroxyflavone (7-HY) is a flavonoid known for its anti-inflammatory, anticarcinogenic, and antioxidant effects. This study aims to assess the ameliorative effects of 7-HY on NAFLD induced by a high-fat diet and elucidate underlying mechanisms. Oleic acid/palmitic acid-induced HepG2 cells and C57BL/6 mice on a high-fat diet were utilized as in vitro and in vivo models. In animal experiments, 7-HY was utilized as a dietary supplement. The 15-week in vivo experiment monitored body weight, body fat percentage, glucose tolerance, insulin tolerance, and metabolic indexes. Commercial kits assessed triglyceride (TG) and total cholesterol levels in cells, liver tissue, and blood. Discovery Studio identified potential targets of 7-HY, compared with NAFLD-associated targets in the GeneCards database. Results indicated 7-HY mitigated fat accumulation, hepatic steatosis, and oxidative stress induced by a high-fat diet. Furthermore, 7-HY showed potential efficacy in ameliorating abnormal glucose metabolism and promoting energy metabolism. Reverse target finding and molecular docking demonstrated a robust interaction between 7-HY and serine/threonine kinase 24 (STK24). Subsequent experimental results confirmed 7-HY's ability to inhibit TG deposition in HepG2 cells through interaction with STK24. In conclusion, 7-HY demonstrated the capacity to alleviate high-fat diet-induced NAFLD, presenting a novel strategy for the prevention and treatment of NAFLD.

Genetic Ablation of STE20-Type Kinase MST4 Does Not Alleviate Diet-Induced MASLD Susceptibility in Mice

Metabolic dysfunction-associated steatotic liver disease (MASLD) and its advanced subtype, metabolic dysfunction-associated steatohepatitis (MASH), have emerged as the most common chronic liver disease worldwide, yet there is no targeted pharmacotherapy presently available. This study aimed to investigate the possible in vivo function of STE20-type protein kinase MST4, which was earlier implicated in the regulation of hepatocellular lipotoxic milieu in vitro, in the control of the diet-induced impairment of systemic glucose and insulin homeostasis as well as MASLD susceptibility. Whole-body and liver-specific Mst4 knockout mice were generated by crossbreeding conditional Mst4fl/fl mice with mice expressing Cre recombinase under the Sox2 or Alb promoters, respectively. To replicate the environment in high-risk subjects, Mst4-/- mice and their wild-type littermates were fed a high-fat or a methionine-choline-deficient (MCD) diet. Different in vivo tests were conducted in obese mice to describe the whole-body metabolism. MASLD progression in the liver and lipotoxic damage to adipose tissue, kidney, and skeletal muscle were analyzed by histological and immunofluorescence analysis, biochemical assays, and protein and gene expression profiling. In parallel, intracellular fat storage and oxidative stress were assessed in primary mouse hepatocytes, where MST4 was silenced by small interfering RNA. We found that global MST4 depletion had no effect on body weight or composition, locomotor activity, whole-body glucose tolerance or insulin sensitivity in obese mice. Furthermore, we observed no alterations in lipotoxic injuries to the liver, adipose, kidney, or skeletal muscle tissue in high-fat diet-fed whole-body Mst4-/- vs. wild-type mice. Liver-specific Mst4-/- mice and wild-type littermates displayed a similar severity of MASLD when subjected to an MCD diet, as evidenced by equal levels of steatosis, inflammation, hepatic stellate cell activation, fibrosis, oxidative/ER stress, and apoptosis in the liver. In contrast, the in vitro silencing of MST4 effectively protected primary mouse hepatocytes against ectopic lipid accumulation and oxidative cell injury triggered by exposure to fatty acids. In summary, these results suggest that the genetic ablation of MST4 in mice does not mitigate the initiation or progression of MASLD and has no effect on systemic glucose or insulin homeostasis in the context of nutritional stress. The functional compensation for the genetic loss of MST4 by yet undefined mechanisms may contribute to the apparent discrepancy between in vivo and in vitro phenotypic consequences of MST4 silencing.

Epinephrine inhibits PI3Kα via the Hippo kinases

The phosphoinositide 3-kinase p110α is an essential mediator of insulin signaling and glucose homeostasis. We interrogated the human serine, threonine, and tyrosine kinome to search for novel regulators of p110α and found that the Hippo kinases phosphorylate p110α at T1061, which inhibits its activity. This inhibitory state corresponds to a conformational change of a membrane-binding domain on p110α, which impairs its ability to engage membranes. In human primary hepatocytes, cancer cell lines, and rodent tissues, activation of the Hippo kinases MST1/2 using forskolin or epinephrine is associated with phosphorylation of T1061 and inhibition of p110α, impairment of downstream insulin signaling, and suppression of glycolysis and glycogen synthesis. These changes are abrogated when MST1/2 are genetically deleted or inhibited with small molecules or if the T1061 is mutated to alanine. Our study defines an inhibitory pathway of PI3K signaling and a link between epinephrine and insulin signaling.

Signaling pathways and intervention for therapy of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) represents one of the fastest growing epidemic metabolic disorders worldwide and is a strong contributor for a broad range of comorbidities, including vascular, visual, neurological, kidney, and liver diseases. Moreover, recent data suggest a mutual interplay between T2DM and Corona Virus Disease 2019 (COVID-19). T2DM is characterized by insulin resistance (IR) and pancreatic β cell dysfunction. Pioneering discoveries throughout the past few decades have established notable links between signaling pathways and T2DM pathogenesis and therapy. Importantly, a number of signaling pathways substantially control the advancement of core pathological changes in T2DM, including IR and β cell dysfunction, as well as additional pathogenic disturbances. Accordingly, an improved understanding of these signaling pathways sheds light on tractable targets and strategies for developing and repurposing critical therapies to treat T2DM and its complications. In this review, we provide a brief overview of the history of T2DM and signaling pathways, and offer a systematic update on the role and mechanism of key signaling pathways underlying the onset, development, and progression of T2DM. In this content, we also summarize current therapeutic drugs/agents associated with signaling pathways for the treatment of T2DM and its complications, and discuss some implications and directions to the future of this field.

Molecular mechanisms involved in regulating protein activity and biological function of MST3

Mammalian sterile 20-like (Ste20-like) protein kinase 3 (MST3) or serine/threonine-protein kinase 24 (STK24) is a serine/threonine protein kinase that belongs to the mammalian STE20-like protein kinase family. MST3 is a pleiotropic protein that plays a critical role in regulating a variety of events, including apoptosis, immune response, metabolism, hypertension, tumor progression, and development of the central nervous system. The MST3-mediated regulation is intricately related to protein activity, post-translational modification, and subcellular location. Here, we review the recent progress on the regulatory mechanisms against MST3 and its-mediated control of disease progression.

NDR kinase tricornered genetically interacts with Ccm3 and metabolic enzymes in Drosophila melanogaster tracheal development

The Germinal Center Kinase III (GckIII) pathway is a Hippo-like kinase module defined by sequential activation of Ste20 kinases Thousand and One (Tao) and GckIII, followed by nuclear dbf2-related (NDR) kinase Tricornered (Trc). We previously uncovered a role for the GckIII pathway in Drosophila melanogaster tracheal (respiratory) tube morphology. The trachea form a network of branched epithelial tubes essential for oxygen transport, and are structurally analogous to branched tubular organs in vertebrates, such as the vascular system. In the absence of GckIII pathway function, aberrant dilations form in tracheal tubes characterized by mislocalized junctional and apical proteins, suggesting that the pathway is important in maintaining tube integrity in development. Here, we observed a genetic interaction between trc and Cerebral cavernous malformations 3 (Ccm3), the Drosophila ortholog of a human vascular disease gene, supporting our hypothesis that the GckIII pathway functions downstream of Ccm3 in trachea, and potentially in the vertebrate cerebral vasculature. However, how GckIII pathway signaling is regulated and the mechanisms that underpin its function in tracheal development are unknown. We undertook biochemical and genetic approaches to identify proteins that interact with Trc, the most downstream GckIII pathway kinase. We found that known GckIII and NDR scaffold proteins are likely to control GckIII pathway signaling in tracheal development, consistent with their conserved roles in Hippo-like modules. Furthermore, we show genetic interactions between trc and multiple enzymes in glycolysis and oxidative phosphorylation, suggesting a potential function of the GckIII pathway in integrating cellular energy requirements with maintenance of tube integrity.

Serine/threonine-protein kinase STK24 induces tumorigenesis by regulating the STAT3/VEGFA signaling pathway

Lung cancer is the most common cause of cancer-related death. Although anti-angiogenesis therapy has been effective in the treatment of nonsmall cell lung cancer (NSCLC), drug-resistance is a common challenge. Therefore, there is a need to develop new therapeutic strategies for NSCLC. Serine/threonine-protein kinase 24 (STK24), also known as MST3, belongs to the germinal center kinase III subfamily, and the biological function of STK24 in NSCLC tumorigenesis and tumor angiogenesis is still unclear. In this study, we demonstrated that STK24 was overexpressed in lung cancer tissues compared with normal lung tissues, and lung cancer patients with higher STK24 expression levels had shorter overall survival time. In addition, our in vitro assays using A549 and H226 cell lines revealed that the STK24 expression level of cancer cells was positively correlated with cancer cells proliferation, migration, invasion, and tumor angiogenesis ability; in vivo assays also demonstrated that silencing of STK24 dramatically inhibited tumor progress and tumor angiogenesis. To investigate a mechanism, we revealed that STK24 positively regulated the signal transducer and activator of transcription 3 (STAT3)/vascular endothelial growth factor A (VEGFA) signaling pathway by inhibiting polyubiquitin-proteasomal-mediated degradation of STAT3. Furthermore, we performed in vivo assays in BALB/c nude mice and in vitro assays to show that STK24-regulated tumor angiogenesis depends on STAT3. These findings deepened our understanding of tumor angiogenesis, and the STK24/STAT3/VEGFA signaling pathway might be a novel therapeutic target for NSCLC treatment.

GCKIII kinases in lipotoxicity: Roles in NAFLD and beyond

Nonalcoholic fatty liver disease (NAFLD) is defined by excessive accumulation of lipid droplets within hepatocytes. The STE20-type kinases comprising the germinal center kinase III (GCKIII) subfamily - MST3, MST4, and STK25 - decorate intrahepatocellular lipid droplets and have recently emerged as critical regulators of the initiation and progression of NAFLD. While significant advancement has been made toward deciphering the role of GCKIII kinases in hepatic fat accumulation (i.e., steatosis) as well as the aggravation of NAFLD into its severe form nonalcoholic steatohepatitis (NASH), much remains to be resolved. This review provides a brief overview of the recent studies in patient cohorts, cultured human cells, and mouse models, which have characterized the function of MST3, MST4, and STK25 in the regulation of hepatic lipid accretion, meta-inflammation, and associated cell damage in the context of NAFLD/NASH. We also highlight the conflicting data and emphasize future research directions that are needed to advance our understanding of GCKIII kinases as potential targets in the therapy of NAFLD and its comorbidities. Conclusions: Several lines of evidence suggest that GCKIII proteins govern the susceptibility to hepatic lipotoxicity and that pharmacological inhibition of these kinases could mitigate NAFLD development and aggravation. Comprehensive characterization of the molecular mode-of-action of MST3, MST4, and STK25 in hepatocytes as well as extrahepatic tissues is important, especially in relation to their impact on carcinogenesis, to fully understand the efficacy as well as safety of GCKIII antagonism.

Silencing of STE20-type kinase MST3 in mice with antisense oligonucleotide treatment ameliorates diet-induced nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is emerging as a leading cause of chronic liver disease worldwide. Despite intensive nonclinical and clinical research in this field, no specific pharmacological therapy is currently approved to treat NAFLD, which has been recognized as one of the major unmet medical needs of the 21st century. Our recent studies have identified STE20-type kinase MST3, which localizes to intracellular lipid droplets, as a critical regulator of ectopic fat accumulation in human hepatocytes. Here, we explored whether treatment with Mst3-targeting antisense oligonucleotides (ASOs) can promote hepatic lipid clearance and mitigate NAFLD progression in mice in the context of obesity. We found that administration of Mst3-targeting ASOs in mice effectively ameliorated the full spectrum of high-fat diet-induced NAFLD including liver steatosis, inflammation, fibrosis, and hepatocellular damage. Mechanistically, Mst3 ASOs suppressed lipogenic gene expression, as well as acetyl-CoA carboxylase (ACC) protein abundance, and substantially reduced lipotoxicity-mediated oxidative and endoplasmic reticulum stress in the livers of obese mice. Furthermore, we found that MST3 protein levels correlated positively with the severity of NAFLD in human liver biopsies. In summary, this study provides the first in vivo evidence that antagonizing MST3 signaling is sufficient to mitigate NAFLD progression in conditions of excess dietary fuels and warrants future investigations to assess whether MST3 inhibitors may provide a new strategy for the treatment of patients with NAFLD.

Stk24 protects against obesity-associated metabolic disorders by disrupting the NLRP3 inflammasome

Adipose tissue macrophages (ATMs) regulate the occurrence of obesity and its related diseases. Here, we found that serine/threonine protein kinase 24 (Stk24) expression is downregulated significantly in ATMs in obese subjects or obese subjects with type 2 diabetes and mice fed a high-fat diet (HFD). We further identified that glucolipotoxicity downregulated Stk24 expression in ATMs. Stk24-deficient mice develop severe HFD-induced metabolic disorders and insulin insensitivity. Mechanistically, Stk24 intervenes in NLRP3 inflammasome assembly in ATMs by associating directly with NLRP3, decreasing interleukin-1β (IL-1β) secretion. Accordingly, Stk24 deficiency in the hematopoietic system promotes NLRP3 inflammasome activation, which contributes to exacerbation of metabolic disorders. Intriguingly, Stk24 expression correlates negatively with body mass index (BMI) and the levels of glucose, cholesterol, triglycerides, and low-density lipoprotein in human subjects. These findings provide insights into the function and clinical implications of Stk24 in obesity-mediated metabolic disorders.

Reference intervals for routine biochemical markers and body mass index: A study based on healthcare center database in northeastern Iran

Age- and sex-specific reference intervals (RIs) for some biochemical tests may be useful for their interpretation, due to the variations in lifestyle and genetic, or ethnic factors. The aim of this study was to obtain RIs for some routine biochemical markers including a serum lipid profile, fasting blood glucose (FBG), aspartate and alanine aminotransferase (AST and ALT), uric acid, and body mass index (BMI) in subjects who attended primary healthcare centers. The large database of primary healthcare centers uses RIs to report results for children, adolescents, and young and old adults. RIs were obtained by using the indirect method, recommended by the CLSI Ep28-A3 guidelines. RIs for FBG, BMI, and serum lipid profile, including triglyceride, total cholesterol, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol in people aged 18 to 120 years, were obtained without age/sex segmentation. RIs for serum AST, ALT, and uric acid were obtained without age segmentation, though these RIs were higher in males than females. The RIs for AST, ALT, and uric acid were higher in men, while the RIs for the other variables were similar in both sexes. This is the first study reporting the use of indirect RIs for BMI.

Gut microbiota transplantation from db/db mice induces diabetes-like phenotypes and alterations in Hippo signaling in pseudo germ-free mice

Type 2 diabetes mellitus (T2DM) is an age-related metabolic disease that is of increasing concern. Gut microbiota might have a critical role in the pathogenesis of T2DM. Additionally, Hippo signaling has been associated strongly with the progression of T2DM and the aging process. We adopted db/db male mice as a T2DM model, and the gut microbiota of db/db and m/m mice were transplanted successfully into pseudo germ-free mice. Furthermore, Hippo signaling, including mammalian sterile 20-like protein kinases 1 (MST1), large tumor suppressors 1 (LATS1), Yes-associated protein (YAP), and phosphorylation of YAP (p-YAP) in peripheral tissues were significantly altered and highly correlated with blood glucose in db/db mice. Interestingly, the host after gut microbiota transplantation from db/db mice showed decreased MST1 and LATS1 levels, and p-YAP/YAP ratio in the heart, liver, and kidney compared to those from m/m mice. Negative correlations between fasting blood glucose and Hippo signaling levels in selected peripheral tissues also were identified. These findings suggest that alterations in Hippo signaling in selected peripheral tissues may contribute to the development of T2DM, and that therapeutic interventions improving Hippo signaling by gut microbiota transplantation might be beneficial for the treatment of T2DM and other age-related metabolic diseases.

Differential Levels of Hippo Signaling in Selected Brain and Peripheral Tissues in Streptozotocin-Induced Cognitive Dysfunction in Mice

Increasing studies have revealed that metabolic disorders, especially diabetes, are high risk factors for the development of Alzheimer's disease (AD) and other neurodegenerative diseases. It has been reported that patients with diabetes are prone to suffer from cognitive dysfunction (CD). Although abnormal glucose metabolism and deposition of amyloid β (Aβ) are proven to have a closely relationship with diabetes-induced CD, its exact mechanism is still undetermined. In this study, a total of 14 mice were intraperitoneally injected with streptozotocin for 5 consecutive days to mimic diabetic models, and then hierarchical cluster analysis was adopted to classify the diabetic mice into CD and Non-CD phenotypes by the results of Morris water maze test (MWMT). Furthermore, we detected Hippo signaling including mammalian sterile 20-like protein kinases1 (MST1), large tumor suppressors 1 (LATS1), Yes-associated protein (YAP) and phosphorylation of YAP (p-YAP) in brain and peripheral tissues. As compared with control mice, the levels of MST1, LATS1 and p-YAP/YAP ratio were increased in medial prefrontal cortex (mPFC), striatum and hippocampus of CD mice, while these proteins were decreased in gut tissue of CD mice. Additionally, there were significant positive correlations between escape latency and p-YAP/YAP ratio in mPFC, anterior cingulate cortex (ACC) and hippocampus, as well as the level of LATS1 in liver, kidney and gut tissues. In conclusion, alterations in Hippo signaling may contribute to CD induced by diabetes. Therefore, therapeutic interventions improving Hippo signaling might be beneficial to the treatment of diabetes-induced CD and other neurodegenerative diseases.

Protein kinase MST3 modulates lipid homeostasis in hepatocytes and correlates with nonalcoholic steatohepatitis in humans

Ectopic lipid storage in the liver is considered the main risk factor for nonalcoholic steatohepatitis (NASH). Understanding the molecular networks controlling hepatocellular lipid deposition is therefore essential for developing new strategies to effectively prevent and treat this complex disease. Here, we describe a new regulator of lipid partitioning in human hepatocytes: mammalian sterile 20-like (MST) 3. We found that MST3 protein coats lipid droplets in mouse and human liver cells. Knockdown of MST3 attenuated lipid accumulation in human hepatocytes by stimulating β-oxidation and triacylglycerol secretion while inhibiting fatty acid influx and lipid synthesis. We also observed that lipogenic gene expression and acetyl-coenzyme A carboxylase protein abundance were reduced in MST3-deficient hepatocytes, providing insight into the molecular mechanisms underlying the decreased lipid storage. Furthermore, MST3 expression was positively correlated with key features of NASH (i.e., hepatic lipid content, lobular inflammation, and hepatocellular ballooning) in human liver biopsies. In summary, our results reveal a role of MST3 in controlling the dynamic metabolic balance of liver lipid catabolism vs. lipid anabolism. Our findings highlight MST3 as a potential drug target for the prevention and treatment of NASH and related complex metabolic diseases.-Cansby, E., Kulkarni, N. M., Magnusson, E., Kurhe, Y., Amrutkar, M., Nerstedt, A., Ståhlman, M., Sihlbom, C., Marschall, H.-U., Borén, J., Blüher, M., Mahlapuu, M. Protein kinase MST3 modulates lipid homeostasis in hepatocytes and correlates with nonalcoholic steatohepatitis in humans.

MST Kinases and Metabolism

Since the discovery of the mammalian sterile twenty (MST) kinase family of proteins (MST1/STK4, MST2/STK3, MST3/STK24, and SOK1/STK25), much has been done that adds to our knowledge of their structure, regulation, and function. In the last few years, a series of articles has unveiled a previous unknown relation of these kinases with metabolic regulation and the homeostasis of metabolic tissues. The aim of this review is to bring together this body of data to provide a detailed picture of the current knowledge about these proteins, metabolism, and some of the associated diseases.

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.