The Shh coreceptor Cdo is required for differentiation of midbrain dopaminergic neurons

Cdon ablation in motor neurons causes age-related motor neuron degeneration and impaired sciatic nerve repair

BACKGROUND

The functional deterioration and loss of motor neurons are tightly associated with degenerative motor neuron diseases and aging-related muscle wasting. Motor neuron diseases or aging-related muscle wasting in turn contribute to increased risk of adverse health outcomes in the elderly. Cdon (cell adhesion molecule-downregulated oncogene) belongs to the immunoglobulin superfamily of cell adhesion molecule and plays essential roles in multiple signalling pathways, including sonic hedgehog (Shh), netrin, and cadherin-mediated signalling. Cdon as a Shh coreceptor plays a critical role in motor neuron specification during embryonic development. However, its role in adult motor neuron function is unknown.

METHODS

Hb9-Cre recombinase-driven motor neuron-specific Cdon deficient mice (mnKO) and a compound mutant mice (mnKO::SOD1G93A ) were generated to investigate the role of Cdon in motor neuron degeneration. Motor neuron regeneration was examined by using a sciatic nerve crush injury model. To investigate the phenotype, physical activity, compound muscle action potential, immunostaining, and transmission electron microscopy were carried out. In the mechanism study, RNA sequencing and RNA/protein analyses were employed.

RESULTS

Mice lacking Cdon in motor neurons exhibited middle age onset lethality and aging-related decline in motor function. In the sciatic nerve crush injury model, mnKO mice exhibited an impairment in motor function recovery evident by prolonged compound muscle action potential duration (4.63 ± 0.35 vs. 3.93 ± 0.22 s for f/f, P < 0.01) and physical activity. Consistently, neuromuscular junctions of mnKO muscles were incompletely occupied (49.79 ± 5.74 vs. 79.39 ± 3.77% fully occupied neuromuscular junctions for f/f, P < 0.0001), suggesting an impaired reinnervation. The transmission electron microscopy analysis revealed that mnKO sciatic nerves had smaller axon diameter (0.88 ± 0.13 vs. 1.43 ± 0.48 μm for f/f, P < 0.0001) and myelination defects. RNA sequencing of mnKO lumbar spinal cords showed alteration in genes related to neurogenesis, inflammation and cell death. Among the altered genes, ErbB4 and FgfR expressions were significantly altered in mnKO as well as in Cdon-depleted NSC34 motor neuron cells. Consistently, Cdon-depleted NSC34 cells exhibited elevated levels of cleaved Caspase3 and γH2AX proteins, as well as Bax transcription. Cdon-depleted NSC34 cells also exhibited impaired activation of Akt in response to neuregulin-1 (NRG1) treatment.

CONCLUSIONS

Our current data demonstrate the functional importance of Cdon in motor neuron function and nerve repair. Cdon ablation causes alterations in neurotrophin signalling that leads to motor neuron degeneration.

PRMT7 ablation in cardiomyocytes causes cardiac hypertrophy and fibrosis through β-catenin dysregulation

Angiotensin II (AngII) has potent cardiac hypertrophic effects mediated through activation of hypertrophic signaling like Wnt/β-Catenin signaling. In the current study, we examined the role of protein arginine methyltransferase 7 (PRMT7) in cardiac function. PRMT7 was greatly decreased in hypertrophic hearts chronically infused with AngII and cardiomyocytes treated with AngII. PRMT7 depletion in rat cardiomyocytes resulted in hypertrophic responses. Consistently, mice lacking PRMT7 exhibited the cardiac hypertrophy and fibrosis. PRMT7 overexpression abrogated the cellular hypertrophy elicited by AngII, while PRMT7 depletion exacerbated the hypertrophic response caused by AngII. Similar with AngII treatment, the cardiac transcriptome analysis of PRMT7-deficient hearts revealed the alteration in gene expression profile related to Wnt signaling pathway. Inhibition of PRMT7 by gene deletion or an inhibitor treatment enhanced the activity of β-catenin. PRMT7 deficiency decreases symmetric dimethylation of β-catenin. Mechanistic studies reveal that methylation of arginine residue 93 in β-catenin decreases the activity of β-catenin. Taken together, our data suggest that PRMT7 is important for normal cardiac function through suppression of β-catenin activity.

Exploring Sonic Hedgehog Cell Signaling in Neurogenesis: Its Potential Role in Depressive Behavior

Depression is the most prevalent form of neuropsychiatric disorder affecting all age groups globally. As per the estimation of the World Health Organization (WHO), depression will develop into the foremost reason for disability globally by the year 2030. The primary neurobiological mechanism implicated in depression remains ambiguous; however, dysregulation of molecular and signaling transductions results in depressive disorders. Several theories have been developed to explain the pathogenesis of depression, however, none of them completely explained all aspects of depressive-pathogenesis. In the current review, we aimed to explore the role of the sonic hedgehog (Shh) signaling pathway in the development of the depressive disorder and its potential as the therapeutic target. Shh signaling has a crucial function in neurogenesis and neural tube patterning during the development of the central nervous system (CNS). Shh signaling performs a basic function in embryogenesis and hippocampal neurogenesis. Moreover, antidepressants are also known to enhance neurogenesis in the hippocampus, which further suggests the potential of Shh signaling. Furthermore, there is decreased expression of a glioma-associated oncogene (Gli1) and Smoothened (Smo) in depression. Moreover, antidepressants also regulate brain-derived neurotrophic factor (BDNF) and wingless protein (Wnt) signaling, therefore, Shh may be implicated in the pathogenesis of the depressive disorder. Deregulation of Shh signaling in CNS results in neurological disorders such as depression.

Cdo Is Required for Efficient Motor Neuron Generation of Embryonic Stem Cells

Background and Objectives

The directed differentiation of pluripotent stem cells into motor neurons is critical for the development of disease modelling and therapeutics to intervene degenerative motor neuron diseases. Cell surface receptor Cdo functions as a coreceptor for Sonic hedgehog (Shh) with Boc and Gas1 in the patterning of ventral spinal cord neurons including motor neurons. However, the discrete function of Cdo is not fully understood.

Methods and Results

In this study, we examined the role of Cdo in motor neuron generation by utilizing in vitro differentiation of Cdo^+/+ and Cdo^−/− embryonic stem cells (ESCs). In response to Shh, Cdo^−/− ESCs exhibited impaired expression of motor neuron specification markers while dorsal interneuron specification markers were significantly increased, compared to Cdo^+/+ ESCs. Reactivation of Shh signalling pathway with Smoothened (Smo) agonist (SAG) restored motor neuron specification in Cdo^−/− ESCs. In addition, electrophysiological analysis revealed the immature electrical features of Cdo^−/− ESCs-derived neurons which was restored by SAG.

Conclusions

Taken together, these data suggest that Cdo as a Shh coreceptor is required for the induction of motor neuron generation by fully activating Shh signalling pathway and provide additional insights into the biology of motor neuron development.

Indoprofen prevents muscle wasting in aged mice through activation of PDK1/AKT pathway

BACKGROUND

Muscle wasting, resulting from aging or pathological conditions, leads to reduced quality of life, increased morbidity, and increased mortality. Much research effort has been focused on the development of exercise mimetics to prevent muscle atrophy and weakness. In this study, we identified indoprofen from a screen for peroxisome proliferator-activated receptor γ coactivator α (PGC-1α) inducers and report its potential as a drug for muscle wasting.

METHODS

The effects of indoprofen treatment on dexamethasone-induced atrophy in mice and in 3-phosphoinositide-dependent protein kinase-1 (PDK1)-deleted C2C12 myotubes were evaluated by immunoblotting to determine the expression levels of myosin heavy chain and anabolic-related and oxidative metabolism-related proteins. Young, old, and disuse-induced muscle atrophic mice were administered indoprofen (2 mg/kg body weight) by gavage. Body weight, muscle weight, grip strength, isometric force, and muscle histology were assessed. The expression levels of muscle mass-related and function-related proteins were analysed by immunoblotting or immunostaining.

RESULTS

In young (3-month-old) and aged (22-month-old) mice, indoprofen treatment activated oxidative metabolism-related enzymes and led to increased muscle mass. Mechanistic analysis using animal models and muscle cells revealed that indoprofen treatment induced the sequential activation of AKT/p70S6 kinase (S6K) and AMP-activated protein kinase (AMPK), which in turn can augment protein synthesis and PGC-1α induction, respectively. Structural prediction analysis identified PDK1 as a target of indoprofen and, indeed, short-term treatment with indoprofen activated the PDK1/AKT/S6K pathway in muscle cells. Consistent with this finding, PDK1 inhibition abrogated indoprofen-induced AKT/S6K activation and hypertrophic response.

CONCLUSIONS

Our findings demonstrate the effects of indoprofen in boosting skeletal muscle mass through the sequential activation of PDK1/AKT/S6K and AMPK/PGC-1α. Taken together, our results suggest that indoprofen represents a potential drug to prevent muscle wasting and weakness related to aging or muscle diseases.

PRMT7 methylates and suppresses GLI2 binding to SUFU thereby promoting its activation

Cellular senescence is implicated in aging or age-related diseases. Sonic hedgehog (Shh) signaling, an inducer of embryonic development, has recently been demonstrated to inhibit cellular senescence. However, the detailed mechanisms to activate Shh signaling to prevent senescence is not well understood. Here, we demonstrate that Protein arginine methyltransferase 7 (PRMT7) promotes Shh signaling via GLI2 methylation which is critical for suppression of cellular senescence. PRMT7-deficient mouse embryonic fibroblasts (MEFs) exhibited a premature cellular senescence with accompanied increase in the cell cycle inhibitors p16 and p21. PRMT7 depletion results in reduced Shh signaling activity in MEFs while PRMT7 overexpression enhances GLI2-reporter activities that are sensitive to methylation inhibition. PRMT7 interacts with and methylates GLI2 on arginine residues 225 and 227 nearby a binding region of SUFU, a negative regulator of GLI2. This methylation interferes with GLI2-SUFU binding, leading to facilitation of GLI2 nuclear accumulation and Shh signaling. Taken together, these data suggest that PRMT7 induces GLI2 methylation, reducing its binding to SUFU and increasing Shh signaling, ultimately leading to prevention of cellular senescence.

Crosstalk of Intercellular Signaling Pathways in the Generation of Midbrain Dopaminergic Neurons In Vivo and from Stem Cells

Dopamine-synthesizing neurons located in the mammalian ventral midbrain are at the center stage of biomedical research due to their involvement in severe human neuropsychiatric and neurodegenerative disorders, most prominently Parkinson’s Disease (PD). The induction of midbrain dopaminergic (mDA) neurons depends on two important signaling centers of the mammalian embryo: the ventral midline or floor plate (FP) of the neural tube, and the isthmic organizer (IsO) at the mid-/hindbrain boundary (MHB). Cells located within and close to the FP secrete sonic hedgehog (SHH), and members of the wingless-type MMTV integration site family (WNT1/5A), as well as bone morphogenetic protein (BMP) family. The IsO cells secrete WNT1 and the fibroblast growth factor 8 (FGF8). Accordingly, the FGF8, SHH, WNT, and BMP signaling pathways play crucial roles during the development of the mDA neurons in the mammalian embryo. Moreover, these morphogens are essential for the generation of stem cell-derived mDA neurons, which are critical for the modeling, drug screening, and cell replacement therapy of PD. This review summarizes our current knowledge about the functions and crosstalk of these signaling pathways in mammalian mDA neuron development in vivo and their applications in stem cell-based paradigms for the efficient derivation of these neurons in vitro.

SGTb regulates a surface localization of a guidance receptor BOC to promote neurite outgrowth

Neuritogenesis is a critical event for neuronal differentiation and neuronal circuitry formation during neuronal development and regeneration. Our previous study revealed a critical role of a guidance receptor BOC in a neuronal differentiation and neurite outgrowth. However, regulatory mechanisms for BOC signaling pathway remain largely unexplored. In the current study, we have identified Small glutamine-rich tetratricopeptide repeat (TPR)-containing b (SGTb) as a BOC interacting protein through yeast two-hybrid screening. Like BOC, SGTb is highly expressed in brain and P19 embryonal carcinoma (EC) cells differentiated into neuronal cells. BOC and SGTb proteins co-precipitate in mouse brain and differentiated P19 EC cells. Furthermore, BOC and SGTb co-localize in neurites and especially are concentrated at the tip of neurites in various neuronal cells. SGTb depletion attenuates neuronal differentiation of P19 cells through reduction of the surface level of BOC. Additionally, SGTb depletion causes BOC localization at neurite tip, coinciding with decreased p-JNK levels critical for actin cytoskeleton remodeling. The overexpression of SGTb or BOC restores JNK activation in BOC or SGTb-depleted cells, respectively. Finally, SGTb elevates the level of surface-resident BOC in BOC-depleted cells, restoring JNK activation. Taken together, our data suggest that SGTb interacts with BOC and regulates its surface level and consequent JNK activation, thereby promoting neuronal differentiation and neurite outgrowth.

Neogenin, a regulator of adult hippocampal neurogenesis, prevents depressive-like behavior

Adult neurogenesis in hippocampal dentate gyrus (DG) is a complex, but precisely controlled process. Dysregulation of this event contributes to multiple neurological disorders, including major depression. Thus, it is of considerable interest to investigate how adult hippocampal neurogenesis is regulated. Here, we present evidence for neogenin, a multifunctional transmembrane receptor, to regulate adult mouse hippocampal neurogenesis. Loss of neogenin in adult neural stem cells (NSCs) or neural progenitor cells (NPCs) impaired NSCs/NPCs proliferation and neurogenesis, whereas increased their astrocytic differentiation. Mechanistic studies revealed a role for neogenin to positively regulate Gli1, a crucial downstream transcriptional factor of sonic hedgehog, and expression of Gli1 into neogenin depleted NSCs/NPCs restores their proliferation. Further morphological and functional studies showed additional abnormities, including reduced dendritic branches and spines, and impaired glutamatergic neuro-transmission, in neogenin-depleted new-born DG neurons; and mice with depletion of neogenin in NSCs/NPCs exhibited depressive-like behavior. These results thus demonstrate unrecognized functions of neogenin in adult hippocampal NSCs/NPCs-promoting NSCs/NPCs proliferation and neurogenesis and preventing astrogliogenesis and depressive-like behavior, and suggest neogenin regulation of Gli1 signaling as a possible underlying mechanism.

Targeting sonic hedgehog signaling in neurological disorders

Sonic hedgehog (Shh) signaling influences neurogenesis and neural patterning during the development of central nervous system. Dysregulation of Shh signaling in brain leads to neurological disorders like autism spectrum disorder, depression, dementia, stroke, Parkinson's diseases, Huntington's disease, locomotor deficit, epilepsy, demyelinating disease, neuropathies as well as brain tumors. The synthesis, processing and transport of Shh ligand as well as the localization of its receptors and signal transduction in the central nervous system has been carefully reviewed. Further, we summarize the regulation of small molecule modulators of Shh pathway with potential in neurological disorders. In conclusion, further studies are warranted to demonstrate the potential of positive and negative regulators of the Shh pathway in neurological disorders.

Mesocortical Dopamine Phenotypes in Mice Lacking the Sonic Hedgehog Receptor Cdon

Motivated behaviors and many psychopathologies typically involve changes in dopamine release from the projections of the ventral tegmental area (VTA) and/or the substantia nigra pars compacta (SNc). The morphogen Sonic Hedgehog (Shh) specifies fates of midbrain dopamine neurons, but VTA-specific effects of Shh signaling are also being uncovered. In this study, we assessed the role of the Shh receptor Cdon in the development of VTA and SNc dopamine neurons. We find that Cdon is expressed in the proliferating progenitor zone of the embryonic ventral midbrain and that the number of proliferating cells in this region is increased in mouse Cdon(-/-) embryos. Consistent with a role of Shh in the regulation of neuronal proliferation in this region, we find that the number of tyrosine hydroxylase (TH)-positive neurons is increased in the VTA of Cdon(-/-) mice at birth and that this effect endures into adulthood. In contrast, the number of TH-positive neurons in the SNc is not altered in Cdon(-/-) mice at either age. Moreover, adult Cdon(-/-) mice have a greater number of medial prefrontal cortex (mPFC) dopamine presynaptic sites, and increased baseline concentrations of dopamine and dopamine metabolites selectively in this region. Finally, consistent with increased dopamine function in the mPFC, we find that adult Cdon(-/-) mice fail to exhibit behavioral plasticity upon repeated amphetamine treatment. Based on these data, we suggest that Cdon plays an important role encoding the diversity of dopamine neurons in the midbrain, influencing both the development of the mesocortical dopamine pathway and behavioral outputs that involve this neural circuitry.

Prmt7 Deficiency Causes Reduced Skeletal Muscle Oxidative Metabolism and Age-Related Obesity

Maintenance of skeletal muscle function is critical for metabolic health and the disruption of which exacerbates many chronic diseases such as obesity and diabetes. Skeletal muscle responds to exercise or metabolic demands by a fiber-type switch regulated by signaling-transcription networks that remains to be fully defined. Here, we report that protein arginine methyltransferase 7 (Prmt7) is a key regulator for skeletal muscle oxidative metabolism. Prmt7 is expressed at the highest levels in skeletal muscle and decreased in skeletal muscles with age or obesity. Prmt7(-/-) muscles exhibit decreased oxidative metabolism with decreased expression of genes involved in muscle oxidative metabolism, including PGC-1α. Consistently, Prmt7(-/-) mice exhibited significantly reduced endurance exercise capacities. Furthermore, Prmt7(-/-) mice exhibit decreased energy expenditure, which might contribute to the exacerbated age-related obesity of Prmt7(-/-) mice. Similarly to Prmt7(-/-) muscles, Prmt7 depletion in myoblasts also reduces PGC-1α expression and PGC-1α-promoter driven reporter activities. Prmt7 regulates PGC-1α expression through interaction with and activation of p38 mitogen-activated protein kinase (p38MAPK), which in turn activates ATF2, an upstream transcriptional activator for PGC-1α. Taken together, Prmt7 is a novel regulator for muscle oxidative metabolism via activation of p38MAPK/ATF2/PGC-1α.

A Shh coreceptor Cdo is required for efficient cardiomyogenesis of pluripotent stem cells

Sonic hedgehog (Shh) signaling plays an important role for early heart development, such as heart looping and cardiomyogenesis of pluripotent stem cells. A multifunctional receptor Cdo functions as a Shh coreceptor together with Boc and Gas1 to activate Shh signaling and these coreceptors seem to play compensatory roles in early heart development. Thus in this study, we examined the role of Cdo in cardiomyogenesis by utilizing an in vitro differentiation of pluripotent stem cells. Here we show that Cdo is required for efficient cardiomyogenesis of pluripotent stem cells by activation of Shh signaling. Cdo is induced concurrently with Shh signaling activation upon induction of cardiomyogenesis of P19 embryonal carcinoma (EC) cells. Cdo-depleted P19 EC and Cdo(-/-) mouse embryonic stem (ES) cells display decreased expression of key cardiac regulators, including Gata4, Nkx2.5 and Mef2c and this decrease coincides with reduced Shh signaling activities. Furthermore Cdo deficiency causes a stark reduction in formation of mature contractile cardiomyocytes. This defect in cardiomyogenesis is overcome by reactivation of Shh signaling at the early specification stage of cardiomyogenesis. The Shh agonist treatment restores differentiation capacities of Cdo-deficient ES cells into contractile cardiomyocytes by recovering both the expression of early cardiac regulators and structural genes such as cardiac troponin T and Connexin 43. Therefore Cdo is required for efficient cardiomyogenesis of pluripotent stem cells and an excellent target to improve the differentiation potential of stem cells for generation of transplantable cells to treat cardiomyopathies.