The Ca2+/calmodulin-dependent protein kinase kinase, CaMKK2, inhibits preadipocyte differentiation

The involvement of CaMKKI in activating AMPKα in yesso scallop Patinopecten yessoensis under high temperature stress

Calcium/calmodulin dependent protein kinase kinase (CaMKK), a highly conserved protein kinase, is involved in the downstream processes of various biological activities by phosphorylating and activating 5'-AMP-activated protein kinase (AMPK) in response to the increase of cytosolic-free calcium (Ca2+). In the present study, a CaMKKI was identified from Yesso scallop Patinopecten yessoensis. Its mRNA was ubiquitously expressed in haemocytes and all tested tissues with the highest expression level in mantle. The expression level of PyCaMKKI mRNA in adductor muscle was significantly upregulated at 1, 3 and 6 h after high temperature treatment (25 °C), which was 3.43-fold (p < 0.05), 5.25-fold (p < 0.05), and 5.70-fold (p < 0.05) of that in blank group, respectively. At 3 h after high temperature treatment (25 °C), the protein level of PyAMPKα, as well as the phosphorylation level of PyAMPKα at Thr170 in adductor muscle, and the positive co-localized fluorescence signals of PyCaMKKI and PyAMPKα in haemocyte all increased significantly (p < 0.05) compared to blank group (18 °C). The pull-down assay showed that rPyCaMKKI and rPyAMPKα could bind each other in vitro. After PyCaMKKI was silenced by siRNA, the mRNA and protein levels of PyCaMKKI and PyAMPKα, and the phosphorylation level of PyAMPKα at Thr170 in adductor muscle were significantly down-regulated (p < 0.05) compared with the negative control group receiving an injection of siRNA-NC. These results collectively suggested that PyCaMKKI was involved in the activation of PyAMPKα in response to high temperature stress and would be helpful for understanding the function of PyCaMKKI-PyAMPKα pathway in maintaining energy homeostasis under high temperature stress in scallops.

The calcium-calmodulin-dependent protein kinase kinase inhibitor, STO-609, inhibits nicotine-induced currents and intracellular calcium increase in insect neurosecretory cells

Insect neuronal nicotinic acetylcholine receptors (nAChRs) are transmembrane receptors that play a key role in the development and synaptic plasticity of both vertebrates and invertebrates and are considered to be major targets of neonicotinoid insecticides. We used dorsal unpaired median (DUM) neurons, which are insect neurosecretory cells, in order to explore the intracellular mechanisms leading to the regulation of insect neuronal nAChRs in more detail. Using whole-cell patch-clamp and fura-2AM calcium imaging techniques, we found that a novel CaMKK/AMPK pathway could be involved in the intracellular regulation of DUM neuron nAChRs. The CaMKK selective inhibitor, STO, reduced nicotinic current amplitudes, and strongly when co-applied with α-Bgt. Interestingly, intracellular application of the AMPK activator, A-76, prevented the reduction in nicotine-induced currents observed in the presence of the AMPK inhibitor, dorsomorphin. STO prevented the increase in intracellular calcium induced by nicotine, which was not dependent on α-Bgt. Currents induced by 1 mM LMA, a selective activator of nAChR2, were reduced under bath application of STO, and mecamylamine, which blocked nAChR2 subtype, inhibited the increase in intracellular calcium induced by LMA. These findings provide insight into potential complex mechanisms linked to the modulation of the DUM neuron nAChRs and CaMKK pathway.

ATAD3 is a limiting factor in mitochondrial biogenesis and adipogenesis of white adipocyte-like 3T3-L1 cells

ATAD3 is a vital ATPase of the inner mitochondrial membrane of pluri-cellular eukaryotes, with largely unknown functions but early required for organism development as necessary for mitochondrial biogenesis. ATAD3 knock-down in C. elegans inhibits at first the development of adipocyte-like intestinal tissue so we used mouse adipocyte model 3T3-L1 cells to analyze ATAD3 functions during adipogenesis and lipogenesis in a mammalian model. ATAD3 function was studied by stable and transient modulation of ATAD3 expression in adipogenesis- induced 3T3-L1 cells using Knock-Down and overexpression strategies, exploring different steps of adipocyte differentiation and lipogenesis. We show that (i) an increase in ATAD3 is preceding differentiation-induced mitochondrial biogenesis; (ii) downregulation of ATAD3 inhibits adipogenesis, lipogenesis, and impedes overexpression of many mitochondrial proteins; (iii) ATAD3 re-expression rescues the phenotype of ATAD3 KD, and (iv) differentiation and lipogenesis are accelerated by ATAD3 overexpression, but inhibited by expression of a dominant-negative mutant. We further show that the ATAD3 KD phenotype is not due to altered insulin signal but involves a limitation of mitochondrial biogenesis linked to Drp1. These results demonstrate that ATAD3 is limiting for in vitro mitochondrial biogenesis and adipogenesis/lipogenesis and therefore that ATAD3 mutation/over- or under-expression could be involved in adipogenic and lipogenic pathologies.

Whole-exome sequencing combined with postoperative data identify c.1614dup (CAMKK2) as a novel candidate monogenic obesity variant

Early-onset obesity is a rising health concern influenced by heredity. However, many monogenic obesity variants (MOVs) remain to be discovered due to differences in ethnicity and culture. Additionally, patients with known MOVs have shown limited weight loss after bariatric surgery, suggesting it can be used as a screening tool for new candidates. In this study, we performed whole-exome sequencing (WES) combined with postoperative data to detect candidate MOVs in a cohort of 62 early-onset obesity and 9 late-onset obesity patients. Our findings demonstrated that patients with early-onset obesity preferred a higher BMI and waist circumference (WC). We confirmed the efficacy of the method by identifying a mutation in known monogenic obesity gene, PCSK1, which resulted in less weight loss after surgery. 5 genes were selected for further verification, and a frameshift variant in CAMKK2 gene: NM_001270486.1, c.1614dup, (p. Gly539Argfs*3) was identified as a novel candidate MOV. This mutation influenced the improvement of metabolism after bariatric surgery. In conclusion, our data confirm the efficacy of WES combined with postoperative data in detecting novel candidate MOVs and c.1614dup (CAMKK2) might be a promising MOV, which needs further confirmation. This study enriches the human monogenic obesity mutation database and provides a scientific basis for clinically accurate diagnosis and treatment.

Metabolome analysis reveals that cyclic adenosine diphosphate ribose contributes to the regulation of differentiation in mice adipocyte

Adipocytes play a key role in energy storage and homeostasis. Although the role of transcription factors in adipocyte differentiation is known, the effect of endogenous metabolites of low molecular weight remains unclear. Here, we analyzed time-dependent changes in the levels of these metabolites throughout adipocyte differentiation, using metabolome analysis, and demonstrated that there is a positive correlation between cyclic adenosine diphosphate ribose (cADPR) and Pparγ mRNA expression used as a marker of differentiation. We also found that the treatment of C3H10T1/2 adipocytes with cADPR increased the mRNA expression of those marker genes and the accumulation of triglycerides. Furthermore, inhibition of ryanodine receptors (RyR), which are activated by cADPR, caused a significant reduction in mRNA expression levels of the marker genes and triglyceride accumulation in adipocytes. Our findings show that cADPR accelerates adipocytic differentiation via RyR pathway.

The role of TRPV ion channels in adipocyte differentiation: What is the evidence?

Obesity is a complex disorder, and the incidence of obesity continues to rise at an alarming rate worldwide. In particular, the growing incidence of overweight and obesity in children is a major health concern. However, the underlying mechanisms of obesity remain unclear and the efficacy of several approaches for weight loss is limited. As an important calcium-permeable temperature-sensitive cation channel, transient receptor potential vanilloid (TRPV) ion channels directly participate in thermo-, mechano-, and chemosensory responses. Modulation of TRPV ion channel activity can alter the physiological function of the ion channel, leading to neurodegenerative diseases, chronic pain, cancer, and skin disorders. In recent years, increasing studies have demonstrated that TRPV ion channels are abundantly expressed in metabolic organs, including the liver, adipose tissue, skeletal muscle, pancreas, and central nervous system, which has been implicated in various metabolic diseases, including obesity and diabetes mellitus. In addition, as an important process for the pathophysiology of adipocyte metabolism, adipocyte differentiation plays a critical role in obesity. In this review, we focus on the role of TRPV ion channels in adipocyte differentiation to broaden the ideas for prevention and control strategies for obesity.

CaMKK2 is not involved in contraction-stimulated AMPK activation and glucose uptake in skeletal muscle

OBJECTIVE

The AMP-activated protein kinase (AMPK) gets activated in response to energetic stress such as contractions and plays a vital role in regulating various metabolic processes such as insulin-independent glucose uptake in skeletal muscle. The main upstream kinase that activates AMPK through phosphorylation of α-AMPK Thr172 in skeletal muscle is LKB1, however some studies have suggested that Ca2+/calmodulin-dependent protein kinase kinase 2 (CaMKK2) acts as an alternative kinase to activate AMPK. We aimed to establish whether CaMKK2 is involved in activation of AMPK and promotion of glucose uptake following contractions in skeletal muscle.

METHODS

A recently developed CaMKK2 inhibitor (SGC-CAMKK2-1) alongside a structurally related but inactive compound (SGC-CAMKK2-1N), as well as CaMKK2 knock-out (KO) mice were used. In vitro kinase inhibition selectivity and efficacy assays, as well as cellular inhibition efficacy analyses of CaMKK inhibitors (STO-609 and SGC-CAMKK2-1) were performed. Phosphorylation and activity of AMPK following contractions (ex vivo) in mouse skeletal muscles treated with/without CaMKK inhibitors or isolated from wild-type (WT)/CaMKK2 KO mice were assessed. Camkk2 mRNA in mouse tissues was measured by qPCR. CaMKK2 protein expression was assessed by immunoblotting with or without prior enrichment of calmodulin-binding proteins from skeletal muscle extracts, as well as by mass spectrometry-based proteomics of mouse skeletal muscle and C2C12 myotubes.

RESULTS

STO-609 and SGC-CAMKK2-1 were equally potent and effective in inhibiting CaMKK2 in cell-free and cell-based assays, but SGC-CAMKK2-1 was much more selective. Contraction-stimulated phosphorylation and activation of AMPK were not affected with CaMKK inhibitors or in CaMKK2 null muscles. Contraction-stimulated glucose uptake was comparable between WT and CaMKK2 KO muscle. Both CaMKK inhibitors (STO-609 and SGC-CAMKK2-1) and the inactive compound (SGC-CAMKK2-1N) significantly inhibited contraction-stimulated glucose uptake. SGC-CAMKK2-1 also inhibited glucose uptake induced by a pharmacological AMPK activator or insulin. Relatively low levels of Camkk2 mRNA were detected in mouse skeletal muscle, but neither CaMKK2 protein nor its derived peptides were detectable in mouse skeletal muscle tissue.

CONCLUSIONS

We demonstrate that pharmacological inhibition or genetic loss of CaMKK2 does not affect contraction-stimulated AMPK phosphorylation and activation, as well as glucose uptake in skeletal muscle. Previously observed inhibitory effect of STO-609 on AMPK activity and glucose uptake is likely due to off-target effects. CaMKK2 protein is either absent from adult murine skeletal muscle or below the detection limit of currently available methods.

Targeting CaMKK2 Inhibits Actin Cytoskeletal Assembly to Suppress Cancer Metastasis

Triple-negative breast cancers (TNBC) tend to become invasive and metastatic at early stages in their development. Despite some treatment successes in early-stage localized TNBC, the rate of distant recurrence remains high, and long-term survival outcomes remain poor. In a search for new therapeutic targets for this disease, we observed that elevated expression of the serine/threonine kinase calcium/calmodulin (CaM)-dependent protein kinase kinase 2 (CaMKK2) is highly correlated with tumor invasiveness. In validation studies, genetic disruption of CaMKK2 expression or inhibition of its activity with small molecule inhibitors disrupted spontaneous metastatic outgrowth from primary tumors in murine xenograft models of TNBC. High-grade serous ovarian cancer (HGSOC), a high-risk, poor prognosis ovarian cancer subtype, shares many features with TNBC, and CaMKK2 inhibition effectively blocked metastatic progression in a validated xenograft model of this disease. Mechanistically, CaMKK2 increased the expression of the phosphodiesterase PDE1A, which hydrolyzed cyclic guanosine monophosphate (cGMP) to decrease the cGMP-dependent activity of protein kinase G1 (PKG1). Inhibition of PKG1 resulted in decreased phosphorylation of vasodilator-stimulated phosphoprotein (VASP), which in its hypophosphorylated state binds to and regulates F-actin assembly to facilitate cell movement. Together, these findings establish a targetable CaMKK2-PDE1A-PKG1-VASP signaling pathway that controls cancer cell motility and metastasis by impacting the actin cytoskeleton. Furthermore, it identifies CaMKK2 as a potential therapeutic target that can be exploited to restrict tumor invasiveness in patients diagnosed with early-stage TNBC or localized HGSOC.

SIGNIFICANCE

CaMKK2 regulates actin cytoskeletal dynamics to promote tumor invasiveness and can be inhibited to suppress metastasis of breast and ovarian cancer, indicating CaMKK2 inhibition as a therapeutic strategy to arrest disease progression.

CaMKK2 alleviates myocardial ischemia/reperfusion injury by inhibiting oxidative stress and inflammation via the action on the AMPK-AKT-GSK-3β/Nrf2 signaling cascade

OBJECTIVE

Calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2) can regulate numerous biological processes and is implicated in diverse pathological processes. Yet its role in myocardial ischemia/reperfusion (MI/R) injury remains unknown. This project explored the possible functions and mechanisms of CaMKK2 in MI/R injury.

METHODS

A rat model of MI/R in vivo was established using the left anterior descending coronary artery ligation method. Rat cardiomyocytes were exposed to hypoxia/reoxygenation (H/R) in vitro to establish a cell model. Overexpression of CaMKK2 was achieved by infecting recombinant adeno-associated virus or adenovirus expressing CaMKK2. Real-time quantitative PCR, immunoblotting, TTC staining, TUNEL assay, ELISA, oxidative stress detection assays, flow cytometry, and CCK-8 assay were carried out.

RESULTS

A decline in CaMKK2 levels was induced by MI/R in vivo or H/R in vitro. Up-modulation of CaMKK2 in rats ameliorated the cardiac injury evoked by MI/R injury accompanied by suppression of cardiac apoptosis, oxidative stress, and proinflammatory response. Rat cardiomyocytes with CaMKK2 overexpression were also protected from H/R damage by inhibiting apoptosis, oxidative stress, and proinflammatory response. CaMKK2 overexpression led to increased phosphorylation of AMPK, AKT, and GSK-3β, and enhanced activation of Nrf2 under MI/R or H/R conditions. Inhibition of AMPK abolished CaMKK2-mediated Nrf2 activation and relevant cardioprotective effect. Restraint of Nrf2 also diminished CaMKK2-mediated relevant cardioprotective effect.

CONCLUSIONS

Up-regulation of CaMKK2 provides a therapeutic benefit in the rat model of MI/R injury by boosting the Nrf2 pathway through regulation of AMPK/AKT/GSK-3β, which suggests CaMKK2 as a new molecular target for the treatment of MI/R injury.

Ephedra Herb extract ameliorates adriamycin-induced nephrotic syndrome in rats via the CAMKK2/AMPK/mTOR signaling pathway

This study aimed to investigate the effect and mechanisms of Ephedra Herb (EH) extract on adriamycin-induced nephrotic syndrome (NS), providing an experimental basis for the clinical treatment of NS. Hematoxylin and eosin staining, creatinine, urea nitrogen, and kidn injury molecule-1 were used to evaluate the activities of EH extract on renal function. The levels of inflammatory factors and oxidative stress were detected by kits. The levels of reactive oxygen species, immune cells, and apoptosis were measured by flow cytometry. A network pharmacological approach was used to predict the potential targets and mechanisms of EH extract in the treatment of NS. The protein levels of apoptosis-related proteins and CAMKK2, p-CAMKK2, AMPK, p-AMPK, mTOR and p-mTOR in the kidneys were detected by Western blot. The effective material basis of EH extract was screened by MTT assay. The AMPK pathway inhibitor (compound C, CC) was added to investigate the effect of the potent material basis on adriamycin-induced cell injury. EH extract significantly improved renal injury and relieve inflammation, oxidative stress, and apoptosis in rats. Network pharmacology and Western blot results showed that the effect of EH extract on NS may be associated with the CAMKK2/AMPK/mTOR signaling pathway. Moreover, methylephedrine significantly ameliorated adriamycin-induced NRK-52e cell injury. Methylephedrine also significantly improved the phosphorylation of AMPK and mTOR, which were blocked by CC. In sum, EH extract may ameliorate renal injury via the CAMKK2/AMPK/mTOR signaling pathway. Moreover, methylephedrine may be one of the material bases of EH extract.

Ca 2+ /Calmodulin Dependent Protein Kinase Kinase-2 (CaMKK2) promotes Protein Kinase G (PKG)-dependent actin cytoskeletal assembly to increase tumor metastasis

Triple-negative breast cancers (TNBCs) tend to become highly invasive early during cancer development. Despite some successes in the initial treatment of patients diagnosed with early-stage localized TNBC, the rate of metastatic recurrence remains high with poor long-term survival outcomes. Here we show that elevated expression of the serine/threonine-kinase, Calcium/Calmodulin (CaM)-dependent protein kinase kinase-2 (CaMKK2), is highly correlated with tumor invasiveness. We determined that genetic disruption of CaMKK2 expression, or inhibition of its activity, disrupted spontaneous metastatic outgrowth from primary tumors in murine xenograft models of TNBC. High-grade serous ovarian cancer (HGSOC), a high-risk, poor-prognosis ovarian cancer subtype, shares many genetic features with TNBC, and importantly, CaMKK2 inhibition effectively blocked metastatic progression in a validated xenograft model of this disease. Probing the mechanistic links between CaMKK2 and metastasis we defined the elements of a new signaling pathway that impacts actin cytoskeletal dynamics in a manner which increases cell migration/invasion and metastasis. Notably, CaMKK2 increases the expression of the phosphodiesterase PDE1A which decreases the cGMP-dependent activity of protein kinase G1 (PKG1). This inhibition of PKG1 results in decreased phosphorylation of Vasodilator-Stimulated Phosphoprotein (VASP), which in its hypophosphorylated state binds to and regulates F-actin assembly to facilitate contraction/cell movement. Together, these data establish a targetable CaMKK2-PDE1A-PKG1-VASP signaling pathway that controls cancer cell motility and metastasis. Further, it credentials CaMKK2 as a therapeutic target that can be exploited in the discovery of agents for use in the neoadjuvant/adjuvant setting to restrict tumor invasiveness in patients diagnosed with early-stage TNBC or localized HGSOC.

β-Carotene induces UCP1-independent thermogenesis via ATP-consuming futile cycles in 3T3-L1 white adipocytes

The activation of brown fat and induction of beige adipocytes, so-called non-shivering thermogenesis, is emerging as a promising target for therapeutic intervention in obesity management. Our previous report demonstrated that β-carotene (BC) induces beige adipocytes to increase UCP1-dependent thermogenic activity. However, the UCP1-independent thermogenic effect of BC on adipose tissues remains unexplored. In this study, we examined the effects of BC on UCP1-independent thermogenic activity with a focus on the ATP-consuming futile cycles in 3T3-L1 adipocytes. BC increased intracellular calcium levels and stimulated the expression of calcium cycling-related proteins, including sarcoendoplasmic reticulum Ca²⁺-ATPase (SERCA) 2b, ryanodine receptor 2 (RyR2), voltage-dependent anion channel (VDAC), mitochondrial calcium uniporter (MCU), and Ca²⁺/calmodulin-dependent protein kinase 2 (CaMK2) in 3T3-L1 white adipocytes. In addition, BC stimulated thermogenesis by activating the creatine metabolism-related thermogenic pathway. Moreover, BC activated β-carotene oxygenase 1 (BCO1), which efficiently cleaved BC to retinal and consequently converted to its transcriptionally active form retinoic acid. These BC conversion products also exhibited thermogenic effects comparable to a similar level of BC. The mechanistic study revealed that retinal exhibited thermogenic activity independently of retinoic acid and retinoic acid-mediated thermogenesis was resulted partly from conversion of retinal. Moreover, BC activated α1-AR and UCP1-independent thermogenic effectors independently of UCP1 expression. In conclusion, the thermogenic response to BC and its conversion products in 3T3-L1 white adipocytes involves two interacting pathways, one mediated via β3-adrenergic receptors (β3-AR) and cyclic adenosine monophosphate (cAMP) and the other via α1-AR and increases in cytosolic Ca²⁺ levels activated by calcium regulatory proteins.

Geraniin targeting CaMKK2 inhibits lipid accumulation in 3T3-L1 adipocytes by suppressing lipogenesis

Obesity has become a worldwide burden and is associated with severe medical complications. Geraniin is a polyphenolic compound that has a wide range of bioactive properties. There is also evidence to support its pharmacological effects on improving lipid accumulation and obesity. This research investigates the effect of geraniin on lipid accumulation in adipocytes and the underlying mechanism. Mature adipocytes were differentiated from immature 3T3-L1 cells. Oil Red O staining and a triglyceride content determination were conducted to evaluate the intracellular lipid accumulation. Molecular docking studies were performed to determine the interaction between geraniin and the key proteins. Western blotting was used to detect the expression of lipogenic enzymes and transcription factors. Geraniin dose-dependently inhibited lipid accumulation in adipocytes by reducing the expression of fatty acid synthase and increasing the phosphorylation level of acetyl-coenzyme A carboxylase. Moreover, geraniin promoted the phosphorylation of AMP-activated protein kinase (AMPK) and further reduced the expression of lipogenic transcription factors (peroxisome proliferator-activated receptor gamma and CCAAT/enhancer binding protein alpha). The expression of the calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2) was increased by the geraniin administration. The molecular docking study demonstrated that geraniin can interact with CaMKK2, which is an upstream kinase of AMPK. A selective CaMKK2 inhibitor reversed the suppressive effect of geraniin on lipogenesis. Geraniin targeted CaMKK2 to inhibit lipid accumulation in 3T3-L1 adipocytes by suppressing lipogenesis, and this supports its potential as a candidate natural anti-obesity drug.

SGC-CAMKK2-1: A Chemical Probe for CAMKK2

The serine/threonine protein kinase calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) plays critical roles in a range of biological processes. Despite its importance, only a handful of inhibitors of CAMKK2 have been disclosed. Having a selective small molecule tool to interrogate this kinase will help demonstrate that CAMKK2 inhibition can be therapeutically beneficial. Herein, we disclose SGC-CAMKK2-1, a selective chemical probe that targets CAMKK2.

Proteomic analysis reveals semaglutide impacts lipogenic protein expression in epididymal adipose tissue of obese mice

BACKGROUND AND OBJECTIVES

Obesity is a global health problem with few pharmacologic options. Semaglutide is a glucagon-like peptide-1 (GLP-1) analogue that induces weight loss. Yet, the role of semaglutide in adipose tissue has not yet been examined. The following study investigated the mechanism of semaglutide on lipid metabolism by analyzing proteomics of epididymal white adipose tissue (eWAT) in obese mice.

METHODS

A total of 36 C57BL/6JC mice were randomly divided into a normal-chow diet group (NCD, n = 12), high-fat diet (HFD, n = 12), and HFD+semaglutide group (Sema, n = 12). Mice in the Sema group were intraperitoneally administered semaglutide, and the HFD group and the NCD group were intraperitoneally administered an equal volume of normal saline. Serum samples were collected to detect fasting blood glucose and blood lipids. The Intraperitoneal glucose tolerance test (IPGTT) was used to measure the blood glucose value at each time point and calculate the area under the glucose curve. Tandem Mass Tag (TMT) combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) were used to study the expression of eWAT, while cellular processes, biological processes, corresponding molecular functions, and related network molecular mechanisms were analyzed by bioinformatics.

RESULTS

Compared with the model group, the semaglutide-treated mice presented 640 differentially expressed proteins (DEPs), including 292 up-regulated and 348 down-regulated proteins. Bioinformatics analysis showed a reduction of CD36, FABP5, ACSL, ACOX3, PLIN2, ANGPTL4, LPL, MGLL, AQP7, and PDK4 involved in the lipid metabolism in the Sema group accompanied by a decrease in visceral fat accumulation, blood lipids, and improvement in glucose intolerance.

CONCLUSION

Semaglutide can effectively reduce visceral fat and blood lipids and improve glucose metabolism in obese mice. Semaglutide treatment might have beneficial effects on adipose tissues through the regulation of lipid uptake, lipid storage, and lipolysis in white adipose tissue.

Cyclic mechanical stretch regulates the AMPK/Egr1 pathway in tenocytes via Ca2+-mediated mechanosensing

PURPOSE

Mechanical stimuli are essential for the maintenance of tendon tissue homeostasis. The study aims to elucidate the mechanobiological mechanisms underlying the maintenance of tenocyte homeostasis by cyclic mechanical stretch under high-glucose (HG) condition.

MATERIALS AND METHODS

Primary tenocytes were isolated from rat Achilles tendon and 2D-cultured under HG condition. The in vitro effects of a single bout, 2-h cyclic biaxial stretch session (1 Hz, 8%) on primary rat tenocytes were explored through Flexcell system. Cell viability, tenogenic gene expression, intracellular calcium concentration, focal adhesion kinase (FAK) expression, and signaling pathway activation were analyzed in tenocytes with or without mechanical stretch.

RESULTS

Mechanical stretch increased tenocyte proliferation and upregulated early growth response protein 1 (Egr1) expression. An increase in intracellular calcium was observed after 30 min of stretching. Mechanical stretch phosphorylated FAK, calmodulin-dependent protein kinase kinase 2 (CaMKK2), and 5' adenosine monophosphate-activated protein kinase (AMPK) in a time-dependent manner, and these effects were abrogated after blocking intracellular calcium. Inhibition of FAK, CaMKK2, and AMPK downregulated the expression of Egr1. In addition, mechanical stretch reinforced cytoskeletal organization via calcium (Ca2+)/FAK signaling.

CONCLUSIONS

Our study demonstrated that mechanical stretch-induced calcium influx activated CaMKK2/AMPK signaling and FAK-cytoskeleton reorganization, thereby promoting the expression of Egr1, which may help maintain tendon cell characteristics and homeostasis in the context of diabetic tendinopathy.

Molecular Mechanisms Underlying Ca2+/Calmodulin-Dependent Protein Kinase Kinase Signal Transduction

Ca²⁺/calmodulin-dependent protein kinase kinase (CaMKK) is the activating kinase for multiple downstream kinases, including CaM-kinase I (CaMKI), CaM-kinase IV (CaMKIV), protein kinase B (PKB/Akt), and 5′AMP-kinase (AMPK), through the phosphorylation of their activation-loop Thr residues in response to increasing the intracellular Ca²⁺ concentration, as CaMKK itself is a Ca²⁺/CaM-dependent enzyme. The CaMKK-mediated kinase cascade plays important roles in a number of Ca²⁺-dependent pathways, such as neuronal morphogenesis and plasticity, transcriptional activation, autophagy, and metabolic regulation, as well as in pathophysiological pathways, including cancer progression, metabolic syndrome, and mental disorders. This review focuses on the molecular mechanism underlying CaMKK-mediated signal transduction in normal and pathophysiological conditions. We summarize the current knowledge of the structural, functional, and physiological properties of the regulatory kinase, CaMKK, and the development and application of its pharmacological inhibitors.

Orosomucoid 2 maintains hepatic lipid homeostasis through suppression of de novo lipogenesis

Non-alcoholic fatty liver disease (NAFLD) is caused by imbalance in lipid metabolism. In this study, we show that the hepatokine orosomucoid (ORM) 2 is a key regulator of de novo lipogenesis in the liver. Hepatic and plasma ORM2 levels are markedly decreased in obese murine models and patients with NAFLD. Through multiple loss- and gain-of function studies, we demonstrate that ORM2 is essential to maintain hepatic and systemic lipid homeostasis. At the mechanistic level, ORM2 binds to inositol 1, 4, 5-trisphosphate receptor type 2 to activate AMP-activated protein kinase signaling, thereby inhibiting sterol regulatory element binding protein 1c-mediated lipogenic gene program. Notably, intraperitoneal injections of recombinant ORM2 protein or stabilized ORM2-FC fusion protein markedly improved liver steatosis, steatohepatitis and atherosclerosis in preclinical mouse models, without adverse effects on body weight or food intake. Thus, these findings suggest that ORM2 may serve as a potential target for therapeutic intervention in NAFLD, non-alcoholic steatohepatitis and related lipid disorders.

Signaling pathways in obesity: mechanisms and therapeutic interventions

Obesity is a complex, chronic disease and global public health challenge. Characterized by excessive fat accumulation in the body, obesity sharply increases the risk of several diseases, such as type 2 diabetes, cardiovascular disease, and nonalcoholic fatty liver disease, and is linked to lower life expectancy. Although lifestyle intervention (diet and exercise) has remarkable effects on weight management, achieving long-term success at weight loss is extremely challenging, and the prevalence of obesity continues to rise worldwide. Over the past decades, the pathophysiology of obesity has been extensively investigated, and an increasing number of signal transduction pathways have been implicated in obesity, making it possible to fight obesity in a more effective and precise way. In this review, we summarize recent advances in the pathogenesis of obesity from both experimental and clinical studies, focusing on signaling pathways and their roles in the regulation of food intake, glucose homeostasis, adipogenesis, thermogenesis, and chronic inflammation. We also discuss the current anti-obesity drugs, as well as weight loss compounds in clinical trials, that target these signals. The evolving knowledge of signaling transduction may shed light on the future direction of obesity research, as we move into a new era of precision medicine.

Involvement of mechano-sensitive Piezo1 channel in the differentiation of brown adipocytes

Brown adipocytes expend energy via heat production and are a potential target for the prevention of obesity and related metabolic disorders. Piezo1 is a Ca2+-permeable non-selective cation channel activated by mechanical stimuli. Piezo1 is reported to be involved in mechano-sensation in non-sensory tissues. However, the expression and roles of Piezo1 in brown adipocytes have not been well clarified. Here, we generated a brown adipocyte line derived from UCP1-mRFP1 transgenic mice and showed that Piezo1 is expressed in pre-adipocytes. Application of Yoda-1, a Piezo1 agonist, suppressed brown adipocyte differentiation, and this suppression was significantly attenuated by treatment with a Piezo1 antagonist and by Piezo1 knockdown. Furthermore, the suppression of brown adipocyte differentiation by Yoda-1 was abolished by co-treatment with a calcineurin inhibitor. Thus, these results suggest that activation of Piezo1 suppresses brown adipocyte differentiation via the calcineurin pathway.

Systemic Ablation of Camkk2 Impairs Metastatic Colonization and Improves Insulin Sensitivity in TRAMP Mice: Evidence for Cancer Cell-Extrinsic CAMKK2 Functions in Prostate Cancer

Despite early studies linking calcium-calmodulin protein kinase kinase 2 (CAMKK2) to prostate cancer cell migration and invasion, the role of CAMKK2 in metastasis in vivo remains unclear. Moreover, while CAMKK2 is known to regulate systemic metabolism, whether CAMKK2's effects on whole-body metabolism would impact prostate cancer progression and/or related comorbidities is not known. Here, we demonstrate that germline ablation of Camkk2 slows, but does not stop, primary prostate tumorigenesis in the TRansgenic Adenocarcinoma Mouse Prostate (TRAMP) genetic mouse model. Consistent with prior epidemiological reports supporting a link between obesity and prostate cancer aggressiveness, TRAMP mice fed a high-fat diet exhibited a pronounced increase in the colonization of lung metastases. We demonstrated that this effect on the metastatic spread was dependent on CAMKK2. Notably, diet-induced lung metastases exhibited a highly aggressive neuroendocrine phenotype. Concurrently, Camkk2 deletion improved insulin sensitivity in the same mice. Histological analyses revealed that cancer cells were smaller in the TRAMP;Camkk2-/- mice compared to TRAMP;Camkk2+/+ controls. Given the differences in circulating insulin levels, a known regulator of cell growth, we hypothesized that systemic CAMKK2 could promote prostate cancer cell growth and disease progression in part through cancer cell-extrinsic mechanisms. Accordingly, host deletion of Camkk2 impaired the growth of syngeneic murine prostate tumors in vivo, confirming nonautonomous roles for CAMKK2 in prostate cancer. Cancer cell size and mTOR signaling was diminished in tumors propagated in Camkk2-null mice. Together, these data indicate that, in addition to cancer cell-intrinsic roles, CAMKK2 mediates prostate cancer progression via tumor-extrinsic mechanisms. Further, we propose that CAMKK2 inhibition may also help combat common metabolic comorbidities in men with advanced prostate cancer.

Rutin promotes white adipose tissue "browning" and brown adipose tissue activation partially through the calmodulin-dependent protein kinase kinase β/AMP-activated protein kinase pathway

Promoting white adipose tissue (WAT) "browning" and brown adipose tissue (BAT) activation could contribute to increasing energy expenditure. We explored the mechanisms by which the natural compound rutin induced adipose tissue differentiation and ameliorated obesity in vivo and in vitro. 3T3-L1 preadipocytes were cultured in adipogenic differentiation media with/out rutin. Male C57BL/6 mice (n = 6) were fed a high-fat diet (HFD) for 12 weeks with/out rutin. In HFD-fed mice, rutin treatment significantly inhibited weight gain, improved the metabolic profile of plasma samples, decreased the weights of epididymal WAT (eWAT), inguina WAT (iWAT), and liver, and adipocyte size. Furthermore, rutin also increased the expression of uncoupling protein 1 (Ucp-1) and other thermogenic markers in the WAT and BAT. In 3T3-L1 cells, rutin effectively reduced the formation of lipid droplets, stimulated the expression of thermogenic markers, and reduced the expression of adipogenic genes. Additionally, rutin markedly upregulated the AMP-activated protein kinase (AMPK) pathway, and these effects were diminished by treatment with the AMPK inhibitor compound C (CC). Pretreatment with the calmodulin-dependent protein kinase kinase β (CaMKKβ) inhibitor STO-609 blocked the induction of thermogenic markers in 3T3-L1 cells by rutin. Our results indicated that rutin increased energy consumption, induced WAT "browning" and BAT activation, and thus was a promising target for the development of new therapeutic approaches to improve adipose tissue energy metabolism.

MicroRNA-378 regulates adipogenic differentiation in bovine intramuscular preadipocytes by targeting CaMKK2

Intramuscular fat, as one of the most important palatability attribute of beef carcase, is the primary determinant of beef quality. The research of adipogenesis mechanism would provide new insight into intramuscular fatty deposition. Here, the role of microRNA-378 was investigated during bovine adipogenic differentiation. It was revealed that miR-378 expression exists variably in bovine major tissue and organs by RT-qPCR. It was predicted that miR-378 targets CaMKK2, as an AMPKα kinase, by DIANA Tools. For better research, primary preadipocytes with stable transfection for up-/down-regulated expression of miR-378 were constructed by lentiviral vectors with GFP gene. The analyses of qPCR showed that PPARγ and adiponectin mRNA levels increased, but C/EBPβ, pref-1 and CaMKK2 mRNA levels decreased during adipogenic differentiation. When miR-378 was overexpressed, preadipocytes proliferation became slower, there are more cellular lipid droplets, and PPARγ and C/EBPβ mRNA levels were higher, but pref-1, adiponectin and CaMKK2 were lower than control groups. Luciferase assay and western blot analysis validated that miR-378 binds the nucleotide sites of the 3′- untranslated region of CaMKK2, which inhibits the mRNA and protein expression of CaMKK2. These findings suggest that miR-378 promotes adipogenic differentiation in bovine intramuscular preadipocytes by targeting CaMKK2 via AMPK signalling pathway.

Targeting CAMKK2 and SOC Channels as a Novel Therapeutic Approach for Sensitizing Acute Promyelocytic Leukemia Cells to All-Trans Retinoic Acid

Calcium ions (Ca²⁺) play important and diverse roles in the regulation of autophagy, cell death and differentiation. Here, we investigated the impact of Ca²⁺ in regulating acute promyelocytic leukemia (APL) cell fate in response to the anti-cancer agent all-trans retinoic acid (ATRA). We observed that ATRA promotes calcium entry through store-operated calcium (SOC) channels into acute promyelocytic leukemia (APL) cells. This response is associated with changes in the expression profiles of ORAI1 and STIM1, two proteins involved in SOC channels activation, as well as with a significant upregulation of several key proteins associated to calcium signaling. Moreover, ATRA treatment of APL cells led to a significant activation of calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) and its downstream effector AMP-activated protein kinase (AMPK), linking Ca²⁺ signaling to autophagy. Pharmacological inhibition of SOC channels and CAMKK2 enhanced ATRA-induced cell differentiation and death. Altogether, our results unravel an ATRA-elicited signaling pathway that involves SOC channels/CAMKK2 activation, induction of autophagy, inhibition of cellular differentiation and suppression of cell death. We suggest that SOC channels and CAMKK2 may constitute novel drug targets for potentiating the anti-cancer effect of ATRA in APL patients.

Hinge Binder Scaffold Hopping Identifies Potent Calcium/Calmodulin-Dependent Protein Kinase Kinase 2 (CAMKK2) Inhibitor Chemotypes

CAMKK2 is a serine/threonine kinase and an activator of AMPK whose dysregulation is linked with multiple diseases. Unfortunately, STO-609, the tool inhibitor commonly used to probe CAMKK2 signaling, has limitations. To identify promising scaffolds as starting points for the development of high-quality CAMKK2 chemical probes, we utilized a hinge-binding scaffold hopping strategy to design new CAMKK2 inhibitors. Starting from the potent but promiscuous disubstituted 7-azaindole GSK650934, a total of 32 compounds, composed of single-ring, 5,6-, and 6,6-fused heteroaromatic cores, were synthesized. The compound set was specifically designed to probe interactions with the kinase hinge-binding residues. Compared to GSK650394 and STO-609, 13 compounds displayed similar or better CAMKK2 inhibitory potency in vitro, while compounds 13g and 45 had improved selectivity for CAMKK2 across the kinome. Our systematic survey of hinge-binding chemotypes identified several potent and selective inhibitors of CAMKK2 to serve as starting points for medicinal chemistry programs.

A complete map of the Calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) signaling pathway

Calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) is a serine/threonine-protein kinase belonging to the Ca²⁺/calmodulin-dependent protein kinase subfamily. CAMKK2 has an autocatalytic site, which gets exposed when Ca²⁺/calmodulin (CAM) binds to it. This results in autophosphorylation and complete activation of CAMKK2. The three major known downstream targets of CAMKK2 are 5'-adenosine monophosphate (AMP)-activated protein kinase (AMPKα), calcium/calmodulin-dependent protein kinase 1 (CAMK1) and calcium/calmodulin-dependent protein kinase 4 (CAMK4). Activation of these targets by CAMKK2 is important for the maintenance of different cellular and physiological processes within the cell. CAMKK2 is found to be important in neuronal development, bone remodeling, adipogenesis, and systemic glucose homeostasis, osteoclastgensis and postnatal myogensis. CAMKK2 is reported to be involved in pathologies like Duchenne muscular dystrophy, inflammation, osteoporosis and bone remodeling and is also reported to be overexpressed in prostate cancer, hepatic cancer, ovarian and gastric cancer. CAMKK2 is involved in increased cell proliferation and migration through CAMKK2/AMPK pathway in prostate cancer and activation of AKT in ovarian cancer. Although CAMKK2 is a molecule of great importance, a public resource of the CAMKK2 signaling pathway is currently lacking. Therefore, we carried out detailed data mining and documentation of the signaling events associated with CAMKK2 from published literature and developed an integrated reaction map of CAMKK2 signaling. This resulted in the cataloging of 285 reactions belonging to the CAMKK2 signaling pathway, which includes 33 protein-protein interactions, 74 post-translational modifications, 7 protein translocation events, and 22 activation/inhibition events. Besides, 124 gene regulation events and 25 activator/inhibitors involved in CAMKK2 activation were also cataloged. The CAMKK2 signaling pathway map data is made freely accessible through WikiPathway database ( https://www.wikipathways.org/index.php/Pathway:WP4874 ). We expect that data on a signaling map of CAMKK2 will provide the scientific community with an improved platform to facilitate further molecular as well as biomedical investigations on CAMKK2 and its utility in the development of biomarkers and therapeutic targets.

CAMKK2-CAMK4 signaling regulates transferrin trafficking, turnover, and iron homeostasis

Background

Circulatory iron is a hazardous biometal. Therefore, iron is transported in a redox-safe state by a serum glycoprotein - transferrin (TF). Different organs acquire iron from the systemic circulation through a tightly regulated mechanism at the blood-tissue interface which involves receptor-mediated internalization of TF. Thus, abnormal TF trafficking may lead to iron dyshomeostasis associated with several diseases including neurodegeneration. Iron -induced toxicity can cause neuronal damage to iron-sensitive brain regions. Recently, it was discovered that CAMKK2, a calcium (Ca²⁺)/calmodulin-activated kinase, controls receptor-mediated TF trafficking in mouse tissues, specifically in the brain. The biological function of CAMKK2 is mediated through multiple downstream effectors. Both CAMKK2 and one of its downstream kinase, CAMK4, exhibit overlapping expression in mouse brain. The role of CAMK4 in vesicular transport has been reported and loss of CAMKK2 or CAMK4 leads to cognitive defects in mouse. Therefore, it was hypothesized that CAMKK2-CAMK4 signaling regulates receptor-mediated TF trafficking and iron homeostasis which may be responsible for the neuronal malfunction observed in CAMKK2- or CAMK4-deficient mice.

Methods

CAMK4^−/− mouse was used to study tissue-specific turnover of TF, TF-receptor (TFRC) and iron. CRISPR/Cas9-based CAMKK2 and/or CAMK4 deleted human embryonic kidney-derived HEK293 cell clones were used to study the molecular defects in receptor-mediated TF trafficking. Further, a “zero functional G protein” condition in HEK293 cell was exploited to study CAMKK2-CAMK4 signaling-mediated regulation of intracellular Ca²⁺ homeostasis which was linked to calcium signaling during TF trafficking.

Results

Loss of CAMK4 leads to abnormal post-translational modifications (PTMs) and turnover of TF in mouse cerebellum and liver which was associated with iron dyshomeostasis in these tissues. The HEK293 cell-based study revealed that the absence of CAMKK2-CAMK4 signaling altered intracellular Ca²⁺ homeostasis and lead to abnormal calcium signaling during TF trafficking. Also, CAMKK2-CAMK4 signaling deficiency affected the molecular interaction of TF and TF-receptor-associated protein complexes which indicated a potential failure in the recruitment of interacting proteins due to differential PTMs in TF.

Conclusion

Overall, this study established a novel mechanistic link between intracellular Ca²⁺ level, receptor-mediated TF trafficking, and iron homeostasis, all regulated by CAMKK2-CAMK4 signaling.

Molecular Mechanisms of Adipogenesis: The Anti-adipogenic Role of AMP-Activated Protein Kinase

Obesity is now a widespread disorder, and its prevalence has become a critical concern worldwide, due to its association with common co-morbidities like cancer, cardiovascular diseases and diabetes. Adipose tissue is an endocrine organ and therefore plays a critical role in the survival of an individual, but its dysfunction or excess is directly linked to obesity. The journey from multipotent mesenchymal stem cells to the formation of mature adipocytes is a well-orchestrated program which requires the expression of several genes, their transcriptional factors, and signaling intermediates from numerous pathways. Understanding all the intricacies of adipogenesis is vital if we are to counter the current epidemic of obesity because the limited understanding of these intricacies is the main barrier to the development of potent therapeutic strategies against obesity. In particular, AMP-Activated Protein Kinase (AMPK) plays a crucial role in regulating adipogenesis – it is arguably the central cellular energy regulation protein of the body. Since AMPK promotes the development of brown adipose tissue over that of white adipose tissue, special attention has been given to its role in adipose tissue development in recent years. In this review, we describe the molecular mechanisms involved in adipogenesis, the role of signaling pathways and the substantial role of activated AMPK in the inhibition of adiposity, concluding with observations which will support the development of novel chemotherapies against obesity epidemics.

In Depth Analysis of Kinase Cross Screening Data to Identify CAMKK2 Inhibitory Scaffolds

The calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) activates CAMK1, CAMK4, AMPK, and AKT, leading to numerous physiological responses. The deregulation of CAMKK2 is linked to several diseases, suggesting the utility of CAMKK2 inhibitors for oncological, metabolic and inflammatory indications. In this work, we demonstrate that STO-609, frequently described as a selective inhibitor for CAMKK2, potently inhibits a significant number of other kinases. Through an analysis of literature and public databases, we have identified other potent CAMKK2 inhibitors and verified their activities in differential scanning fluorimetry and enzyme inhibition assays. These inhibitors are potential starting points for the development of selective CAMKK2 inhibitors and will lead to tools that delineate the roles of this kinase in disease biology.

Binding and structural analyses of potent inhibitors of the human Ca2+/calmodulin dependent protein kinase kinase 2 (CAMKK2) identified from a collection of commercially-available kinase inhibitors

Calcium/Calmodulin-dependent Protein Kinase Kinase 2 (CAMKK2) acts as a signaling hub, receiving signals from various regulatory pathways and decoding them via phosphorylation of downstream protein kinases - such as AMPK (AMP-activated protein kinase) and CAMK types I and IV. CAMKK2 relevance is highlighted by its constitutive activity being implicated in several human pathologies. However, at present, there are no selective small-molecule inhibitors available for this protein kinase. Moreover, CAMKK2 and its closest human homolog, CAMKK1, are thought to have overlapping biological roles. Here we present six new co-structures of potent ligands bound to CAMKK2 identified from a library of commercially-available kinase inhibitors. Enzyme assays confirmed that most of these compounds are equipotent inhibitors of both human CAMKKs and isothermal titration calorimetry (ITC) revealed that binding to some of these molecules to CAMKK2 is enthalpy driven. We expect our results to advance current efforts to discover small molecule kinase inhibitors selective to each human CAMKK.

CaMKK2 Signaling in Metabolism and Skeletal Disease: a New Axis with Therapeutic Potential

PURPOSE OF REVIEW

Age and metabolic disorders result in the accumulation of advanced glycation endproducts (AGEs), oxidative stress, and inflammation, which cumulatively cause a decline in skeletal health. Bone becomes increasingly vulnerable to fractures and its regenerative capacity diminishes under such conditions. With a rapidly aging population in the USA and the global increase in diabetes, efficacious, multi-dimensional therapies that can treat or prevent skeletal diseases associated with metabolic dysfunction and inflammatory disorders are acutely needed.

RECENT FINDINGS

Ca²⁺/calmodulin-dependent protein kinase kinase 2 (CaMKK2) is a key regulator of nutrient intake, glucose metabolism, insulin production, and adipogenesis. Recent studies suggest a pivotal role for CaMKK2 in bone metabolism, fracture healing, and inflammation. Aside from rekindling previous concepts of CaMKK2 as a potent regulator of whole-body energy homeostasis, this review emphasizes CaMKK2 as a potential therapeutic target to treat skeletal diseases that underlie metabolic conditions and inflammation.

AMP-activated protein kinase complexes containing the β2 regulatory subunit are up-regulated during and contribute to adipogenesis

AMP-activated protein kinase (AMPK) is a heterotrimer of α-catalytic and β- and γ-regulatory subunits that acts to regulate cellular and whole-body nutrient metabolism. The key role of AMPK in sensing energy status has led to significant interest in AMPK as a therapeutic target for dysfunctional metabolism in type 2 diabetes, insulin resistance and obesity. Despite the actions of AMPK in the liver and skeletal muscle being extensively studied, the role of AMPK in adipose tissue and adipocytes remains less well characterised. Small molecules that selectively influence AMPK heterotrimers containing specific AMPKβ subunit isoforms have been developed, including MT47-100, which selectively inhibits complexes containing AMPKβ2. AMPKβ1 and AMPKβ2 are the principal AMPKβ subunit isoforms in rodent liver and skeletal muscle, respectively, yet the contribution of specific AMPKβ isoforms to adipose tissue function, however, remains largely unknown. This study therefore sought to determine the contribution of AMPKβ subunit isoforms to adipocyte biology, focussing on adipogenesis. AMPKβ2 was the principal AMPKβ isoform in 3T3-L1 adipocytes, isolated rodent adipocytes and human subcutaneous adipose tissue, as assessed by the contribution to total cellular AMPK activity. Down-regulation of AMPKβ2 with siRNA inhibited lipid accumulation, cellular adiponectin levels and adiponectin secretion during 3T3-L1 adipogenesis, whereas down-regulation of AMPKβ1 had no effect. Incubation of 3T3-L1 cells with MT47-100 selectively inhibited AMPK complexes containing AMPKβ2 whilst simultaneously inhibiting cellular lipid accumulation as well as cellular levels and secretion of adiponectin. Taken together, these data indicate that increased expression of AMPKβ2 is an important feature of efficient adipogenesis.

IGFBP-2 stimulates calcium/calmodulin-dependent protein kinase kinase 2 activation leading to AMP-activated protein kinase induction which is required for osteoblast differentiation

Insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding proteins-2 (IGFBP-2) function coordinately to stimulate osteoblast differentiation. Induction of AMP-activated protein kinase (AMPK) is required for differentiation and is stimulated by these two factors. These studies were undertaken to determine how these two peptides lead to activation of AMPK. Enzymatic inhibitors and small interfering RNA were utilized to attenuate calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2) activity in osteoblasts, and both manipulations resulted in failure to activate AMPK, thereby resulting in inhibition of osteoblast differentiation. IGFBP-2 and IGF-I stimulated an increase in CaMKK2, and inhibition of IGFBP-2 binding its receptor resulted in failure to induce CaMKK2 and AMPK activation. Injection of a peptide that contained the IGFBP-2 receptor-binding domain into IGFBP-2^-/- mice activated CaMKK2 and injection of a CaMKK2 inhibitor into normal mice inhibited both CamKK2 and AMPK activation in osteoblasts. We conclude that induction of CaMKK2 by IGFBP-2 and IGF-I in osteoblasts is an important signaling event that occurs early in differentiation and is responsible for activation of AMPK, which is required for optimal osteoblast differentiation.

AMPK activation inhibits the functions of myeloid-derived suppressor cells (MDSC): impact on cancer and aging

AMP-activated protein kinase (AMPK) has a crucial role not only in the regulation of tissue energy metabolism but it can also control immune responses through its cooperation with immune signaling pathways, thus affecting immunometabolism and the functions of immune cells. It is known that AMPK signaling inhibits the activity of the NF-κB system and thus suppresses pro-inflammatory responses. Interestingly, AMPK activation can inhibit several major immune signaling pathways, e.g., the JAK-STAT, NF-κB, C/EBPβ, CHOP, and HIF-1α pathways, which induce the expansion and activation of myeloid-derived suppressor cells (MDSC). MDSCs induce an immunosuppressive microenvironment in tumors and thus allow the escape of tumor cells from immune surveillance. Chronic inflammation has a key role in the expansion and activation of MDSCs in both tumors and inflammatory disorders. The numbers of MDSCs also significantly increase during the aging process concurrently with the immunosenescence associated with chronic low-grade inflammation. Increased fatty acid oxidation and lactate produced by aerobic glycolysis are important immunometabolic enhancers of MDSC functions. However, it seems that AMPK signaling regulates the functions of MDSCs in a context-dependent manner. Currently, the activators of AMPK signaling are promising drug candidates for cancer therapy and possibly for the extension of healthspan and lifespan. We will describe in detail the AMPK-mediated regulation of the signaling pathways controlling the expansion and activation of immunosuppressive MDSCs. We will propose that the beneficial effects mediated by AMPK activation, e.g., in cancers and the aging process, could be induced by the inhibition of MDSC functions.

The Multi-Functional Calcium/Calmodulin Stimulated Protein Kinase (CaMK) Family: Emerging Targets for Anti-Cancer Therapeutic Intervention

The importance of Ca²⁺ signalling in key events of cancer cell function and tumour progression, such as proliferation, migration, invasion and survival, has recently begun to be appreciated. Many cellular Ca²⁺-stimulated signalling cascades utilise the intermediate, calmodulin (CaM). The Ca²⁺/CaM complex binds and activates a variety of enzymes, including members of the multifunctional Ca²⁺/calmodulin-stimulated protein kinase (CaMK) family. These enzymes control a broad range of cancer-related functions in a multitude of tumour types. Herein, we explore the cancer-related functions of these kinases and discuss their potential as targets for therapeutic intervention.

Loss of Ca2+/Calmodulin Dependent Protein Kinase Kinase 2 Leads to Aberrant Transferrin Phosphorylation and Trafficking: A Potential Biomarker for Alzheimer's Disease

Ca²⁺/calmodulin-dependent protein kinase kinase 2 (CaMKK2) is a serine/threonine kinase that is activated following an increase in the intracellular Ca²⁺ concentration and activates multiple signaling cascades that control physiologically important neuronal processes. CaMKK2 has been implicated in schizophrenia, bipolar disease, neurodegeneration, and cancer. Using isoelectric focusing (IEF) and mass spectrometry-based proteomic analysis, it was found that knockdown (KD) of CaMKK2 in cultured adult primary dorsal root ganglion (DRG) neurons resulted in the reduction of transferrin (TF) phosphorylation at multiple functionally relevant residues which corresponded to loss of an acidic fraction (pH~3-4) of TF. In vitro studies using CRISPR/Cas9 based CaMKK2 knockout (KO) HEK293 and HepG2 cells lines validated previous findings and revealed that loss of CaMKK2 interfered with TF trafficking and turnover. TF is an iron transporter glycoprotein. Abnormal accumulation of iron and/or deregulated Ca²⁺ homeostasis leads to neurodegeneration in Alzheimer's disease (AD). Therefore, it was hypothesized that aberrant CaMKK2 in AD may lead to aberrant phosphorylated transferrin (P-TF: pH~3-4 fraction) which may serve as a hallmark biomarker for AD. A significant reduction of P-TF in the brain and serum of CaMKK2 KO mice and a triple-transgenic mouse model of AD (3xTg-AD) supported this hypothesis. In addition, analysis of early (< 65 years) and late-stage (>65 years) postmortem human AD cerebrospinal fluid (CSF) and serum samples revealed that aberrant P-TF (pH~3-4 fraction) profile was associated with both early and late-stage AD compared to age-matched controls. This indicates P-TF (pH~3-4 fraction) profile may be useful as a minimally invasive biomarker for AD. In addition, this study provides a link between aberrant CaMKK2 with TF trafficking and turnover which provides a novel insight into the neurodegeneration process.

Androgen Receptor-CaMKK2 Axis in Prostate Cancer and Bone Microenvironment

The skeletal system is of paramount importance in advanced stage prostate cancer (PCa) as it is the preferred site of metastasis. Complex mechanisms are employed sequentially by PCa cells to home to and colonize the bone. Bone-resident PCa cells then recruit osteoblasts (OBs), osteoclasts (OCs), and macrophages within the niche into entities that promote cancer cell growth and survival. Since PCa is heavily reliant on androgens for growth and survival, androgen-deprivation therapy (ADT) is the standard of care for advanced disease. Although it significantly improves survival rates, ADT detrimentally affects bone health and significantly increases the risk of fractures. Moreover, whereas the majority patients with advanced PCa respond favorably to androgen deprivation, most experience a relapse of the disease to a hormone-refractory form within 1-2 years of ADT. The tumor adapts to surviving under low testosterone conditions by selecting for mutations in the androgen receptor (AR) that constitutively activate it. Thus, AR signaling remains active in PCa cells and aids in its survival under low levels of circulating androgens and additionally allows the cancer cells to manipulate the bone microenvironment to fuel its growth. Hence, AR and its downstream effectors are attractive targets for therapeutic interventions against PCa. Ca²⁺/calmodulin-dependent protein kinase kinase 2 (CaMKK2), was recently identified as a key downstream target of AR in coordinating PCa cell growth, survival, and migration. Additionally, this multifunctional serine/threonine protein kinase is a critical mediator of bone remodeling and macrophage function, thus emerging as an attractive therapeutic target downstream of AR in controlling metastatic PCa and preventing ADT-induced bone loss. Here, we discuss the role played by AR-CaMKK2 signaling axis in PCa survival, metabolism, cell growth, and migration as well as the cell-intrinsic roles of CaMKK2 in OBs, OCs, and macrophages within the bone microenvironment.

Hydrogen Sulphide Treatment Increases Insulin Sensitivity and Improves Oxidant Metabolism through the CaMKKbeta-AMPK Pathway in PA-Induced IR C2C12 Cells

Studies have reported attenuation of insulin resistance (IR) by improving phosphorylation of the insulin signalling pathway. However, the upstream molecular signalling pathway is still elusive. In this study, Western blot was used to evaluate the phosphorylation level of the insulin signalling pathway and the AMPK pathway. 2-NBDG was used to evaluate glucose uptake. Ca²⁺ imaging was used to assess change of intracellular Ca²⁺ concentration. We found that NaHS enhanced the intracellular Ca²⁺ concentration and glucose uptake and activated the insulin signalling cascade in a palmitic acid (PA)-induced IR model in C2C12 cells. Furthermore, activation of the IRS1/PI3K/AKT pathway and glucose uptake were decreased when AMPK or CaMKKβ was inhibited. Our study also showed that the mitochondrial electron transport chain, ATP production, and intramitochondrial cAMP declined in the IR model but that this effect was reversed by NaHS, an effect that may be mediated by the Ca²⁺/CaMKK2/AMPK and PI3K/AKT pathways. Our data indicate that H₂S improves activation of the insulin signalling cascade and glucose uptake via activation of the Ca²⁺/CaMKK2/AMPK pathway and mitochondrial metabolism in C2C12 cells. Furthermore, NaHS protects mitochondrial function and maintains normal ATP production by activating the cAMP system and the Ca²⁺/CaMKK2/AMPK and PI3K/ATK pathways.

Role of mitochondrial dysfunction and dysregulation of Ca2+ homeostasis in the pathophysiology of insulin resistance and type 2 diabetes

Metabolic diseases such as obesity, type 2 diabetes (T2D) and insulin resistance have attracted great attention from biomedical researchers and clinicians because of the astonishing increase in its prevalence. Decrease in the capacity of oxidative metabolism and mitochondrial dysfunction are a major contributor to the development of these metabolic disorders. Recent studies indicate that alteration of intracellular Ca²⁺ levels and downstream Ca²⁺-dependent signaling pathways appear to modulate gene transcription and the activities of many enzymes involved in cellular metabolism. Ca²⁺ uptake into mitochondria modulates a number of Ca²⁺-dependent proteins and enzymes participating in fatty acids metabolism, tricarboxylic acid cycle, oxidative phosphorylation and apoptosis in response to physiological and pathophysiological conditions. Mitochondrial calcium uniporter (MCU) complex has been identified as a major channel located on the inner membrane to regulate Ca²⁺ transport into mitochondria. Recent studies of MCU complex have increased our understanding of the modulation of mitochondrial function and retrograde signaling to the nucleus via regulation of the mitochondrial Ca²⁺ level. Mitochondria couple cellular metabolic state by regulating not only their own Ca²⁺ levels, but also influence the entire network of cellular Ca²⁺ signaling. The mitochondria-associated ER membranes (MAMs), which are specialized structures between ER and mitochondria, are responsible for efficient communication between these organelles. Defects in the function or structure of MAMs have been observed in affected tissue cells in metabolic disease or neurodegenerative disorders. We demonstrated that dysregulation of intracellular Ca²⁺ homeostasis due to mitochondrial dysfunction or defects in the function of MAMs are involved in the pathogenesis of insulin insensitivity and T2D. These observations suggest that mitochondrial dysfunction and disturbance of Ca²⁺ homeostasis warrant further studies to assist the development of therapeutics for prevention and medication of insulin resistance and T2D.

Extracellular calcium modulates brown adipocyte differentiation and identity

Brown adipocytes are important in regulating non-shivering thermogenesis, whole body glucose and lipid homeostasis. Increasing evidence supports an important role of metabolites as well as macro- and micronutrients in brown adipocyte differentiation and function. Calcium is one of the most abundant ions in the body regulating multiple cellular processes. We observed that increasing extracellular calcium concentration during brown adipocyte differentiation blocks lipid accumulation and suppresses induction of major adipogenic transcription factors such as PPARγ and C/EBPα. In contrast, the depletion of calcium in the medium enhances adipogenesis and expression of brown adipocyte selective genes, such as UCP1. Mechanistically, we show that elevated extracellular calcium inhibits C/EBPβ activity through hyperactivation of ERK, a process that is independent of intracellular calcium levels and reversibly halts differentiation. Moreover, increased extracellular calcium solely after the induction phase of differentiation specifically suppresses gene expression of UCP1, PRDM16 and PGC1-α. Notably, depleting extracellular calcium provokes opposite effects. Together, we show that modulating extracellular calcium concentration controls brown adipocyte differentiation and thermogenic gene expression, highlighting the importance of tissue microenvironment on brown adipocyte heterogeneity and function.

CaMKK2 Suppresses Muscle Regeneration through the Inhibition of Myoblast Proliferation and Differentiation

Skeletal muscle has a major role in locomotion and muscle disorders are associated with poor regenerative efficiency. Therefore, a deeper understanding of muscle regeneration is needed to provide a new insight for new therapies. CaMKK2 plays a role in the calcium/calmodulin-dependent kinase cascade; however, its role in skeletal muscle remains unknown. Here, we found that CaMKK2 expression levels were altered under physiological and pathological conditions including postnatal myogensis, freeze or cardiotoxin-induced muscle regeneration, and Duchenne muscular dystrophy. Overexpression of CaMKK2 suppressed C2C12 myoblast proliferation and differentiation, while inhibition of CaMKK2 had opposite effect. We also found that CaMKK2 is able to activate AMPK in C2C12 myocytes. Inhibition of AMPK could attenuate the effect of CaMKK2 overexpression, while AMPK agonist could abrogate the effect of CaMKK2 knockdown on C2C12 cell differentiation and proliferation. These results suggest that CaMKK2 functions as an AMPK kinase in muscle cells and AMPK mediates the effect of CaMKK2 on myoblast proliferation and differentiation. Our data also indicate that CaMKK2 might inhibit myoblast proliferation through AMPK-mediated cell cycle arrest by inducing cdc2-Tyr15 phosphorylation and repress differentiation through affecting PGC1α transcription. Lastly, we show that overexpressing CaMKK2 in the muscle of mice via electroporation impaired the muscle regeneration during freeze-induced injury, indicating that CaMKK2 could serve as a potential target to treat patients with muscle injury or myopathies. Together, our study reveals a new role for CaMKK2 as a negative regulator of myoblast differentiation and proliferation and sheds new light on the molecular regulation of muscle regeneration.

The Ca(2+)/Calmodulin/CaMKK2 Axis: Nature's Metabolic CaMshaft

Calcium (Ca(2+)) is an essential ligand that binds its primary intracellular receptor calmodulin (CaM) to trigger a variety of downstream processes and pathways. Central to the actions of Ca(2+)/CaM is the activation of a highly conserved Ca(2+)/CaM kinase (CaMK) cascade that amplifies Ca(2+) signals through a series of subsequent phosphorylation events. Proper regulation of Ca(2+) flux is necessary for whole-body metabolism and disruption of Ca(2+) homeostasis has been linked to various metabolic diseases. Here we provide a synthesis of recent advances that highlight the roles of the Ca(2+)/CaMK axis in key metabolic tissues. An appreciation of this information is critical to understanding the mechanisms by which Ca(2+)/CaM-dependent signaling contributes to metabolic homeostasis and disease.

Activation of TRPV2 negatively regulates the differentiation of mouse brown adipocytes

Transient receptor potential vanilloid 2 (TRPV2) acts as a Ca(2+)-permeable non-selective cation channel that has been reported to be sensitive to temperature, mechanical force, and some chemicals. We recently showed that TRPV2 is critical for maintenance of the thermogenic function of brown adipose tissue in mice. However, the involvement of TRPV2 in the differentiation of brown adipocytes remains unexplored. We found that the expression of TRPV2 was dramatically increased during the differentiation of brown adipocytes. Non-selective TRPV2 agonists (2-aminoethoxydiphenyl borate and lysophosphatidylcholine) inhibited the differentiation of brown adipocytes in a dose-dependent manner during the early stage of differentiation of brown adipocytes. The inhibition was rescued by a TRPV2-selective antagonist, SKF96365 (SKF). Mechanical force, which activates TRPV2, also inhibited the differentiation of brown adipocytes in a strength-dependent manner, and the effect was reversed by SKF. In addition, the inhibition of adipocyte differentiation by either TRPV2 ligand or mechanical stimulation was significantly smaller in the cells from TRPV2KO mice. Moreover, calcineurin inhibitors, cyclosporine A and FK506, partially reversed TRPV2 activation-induced inhibition of brown adipocyte differentiation. Thus, we conclude that TRPV2 might be involved in the modulation of brown adipocyte differentiation partially via a calcineurin pathway.

Research Resource: Roles for Calcium/Calmodulin-Dependent Protein Kinase Kinase 2 (CaMKK2) in Systems Metabolism

A number of epidemiological studies have implicated calcium (Ca(2+)) signaling as a major factor in obesity that contributes to aberrant systems metabolism. Somewhat paradoxically, obesity correlates with decreased circulating Ca(2+) levels, leading to increased release of intracellular Ca(2+) stores from the endoplasmic reticulum. These findings suggest that insulin resistance associated with the obese state is linked to activation of canonical Ca(2+) signaling pathways. Mechanistically, increased intracellular Ca(2+) binds calmodulin (CaM) to activate a set of Ca(2+)/CaM-dependent protein kinases. In this research resource, we explore the metabolic functions and implications of Ca(2+)/CaM-dependent protein kinase kinase 2 (CaMKK2) as a metabolic effector of Ca(2+)/CaM action. We reveal the importance of CaMKK2 for gating insulin release from pancreatic β-cells while concomitantly influencing the sensitivity of insulin-responsive tissues. To provide a better understanding of the metabolic impact of CaMKK2 loss, we performed targeted metabolomic analyses of key metabolic byproducts of glucose, fatty acid, and amino acid metabolism in mice null for CaMKK2. We quantified amino acids and acyl carnitines in 3 insulin-sensitive tissues (liver, skeletal muscle, plasma) isolated from CaMKK2(-/-) mice and their wild-type littermates under conditions of dietary stress (low-fat diet, normal chow, high-fat diet, and fasting), thereby unveiling unique metabolic functions of CaMKK2. Our findings highlight CaMKK2 as a molecular rheostat for insulin action and emphasize the importance of Ca(2+)/CaM/CaMKK2 in regulation of whole-body metabolism. These findings reveal that CaMKK2 may be an attractive therapeutic target for combatting comorbidities associated with perturbed insulin signaling.

Vasopressin-induced Ca(2+) signals in human adipose-derived stem cells

Intracellular Ca(2+) signals are essential for stem cell differentiation due to their ability to control signaling pathways involved in this process. Arginine vasopression (AVP) is a neurohypophyseal hormone that increases intracellular Ca(2+) concentration during adipogenesis via V1a receptors, Gq-proteins and the PLC-IP3 pathway in human adipose-derived stromal/stem cells (hASCs). These Ca(2+) signals originate through calcium release from pools within the endoplasmic reticulum and the extracellular space. AVP supplementation to the adipogenic media inhibits adipogenesis and key adipocyte marker genes. This review focuses on the intersection between AVP, Ca(2+) signals and ASC differentiation.

Anti-apoptotic effects of PCP4/PEP19 in human breast cancer cell lines: a novel oncotarget

The PCP4/PEP19 is a calmodulin-binding anti-apoptotic peptide in neural cells but its potential role in human cancer has largely been unknown. We investigated the expression of PCP4/PEP19 in human breast cancer cell lines MCF-7, SK-BR-3, and MDA-MB-231 cells, and found that estrogen receptor (ER)-positive MCF-7 and ER-negative SK-BR-3 cells expressed PCP4/PEP19. In the MCF-7 cells, cell proliferation was estrogen-dependent, and PCP4/PEP19 expression was induced by estrogen. In both cell lines, PCP4/PEP19 knockdown induced apoptosis and slightly decreased Akt phosphorylation. Knockdown of calcium/calmodulin-dependent protein kinase kinase 1 (CaMKK1), resulting in decreased phospho-Akt^Thr308, enhanced apoptosis in SK-BR-3 but not in MCF-7 cells. CaMKK2 knockdown moderately decreased phospho-Akt^Thr308 and increased apoptosis in MCF-7 cells but not in SK-BR-3 cells. These data indicated that PCP4/PEP19 regulates apoptosis but exact mechanism is still unknown. PCP4/PEP19 can therefore potentially serve as independent oncotarget for therapy of PCP4/PEP19-positive breast cancers irrespective of ER expression.