Background: The mitogen-activated protein (MAP) kinases p44^ERK1 and p42^ERK2 are crucial components of the regulatory machinery underlying normal and malignant cell proliferation. A currently accepted model maintains that ERK1 and ERK2 are regulated similarly and contribute to intracellular signaling by phosphorylating a largely common subset of substrates, both in the cytosol and in the nucleus. Results: Here, we show that ablation of ERK1 in mouse embryo fibroblasts and NIH 3T3 cells by gene targeting and RNA interference results in an enhancement of ERK2-dependent signaling and in a significant growth advantage. By contrast, knockdown of ERK2 almost completely abolishes normal and Ras-dependent cell proliferation. Ectopic expression of ERK1 but not of ERK2 in NIH 3T3 cells inhibits oncogenic Ras-mediated proliferation and colony formation. These phenotypes are independent of the kinase activity of ERK1, as expression of a catalytically inactive form of ERK1 is equally effective. Finally, ectopic expression of ERK1 but not ERK2 is sufficient to attenuate Ras-dependent tumor formation in nude mice. Conclusion: These results reveal an unexpected interplay between ERK1 and ERK2 in transducing Ras-dependent cell signaling and proliferation. Whereas ERK2 seems to have a positive role in controlling normal and Ras-dependent cell proliferation, ERK1 probably affects the overall signaling output of the cell by antagonizing ERK2 activity.

Satellite cells are myogenic precursors that proliferate, activate, and differentiate on muscle injury to sustain the regenerative capacity of adult skeletal muscle; in this process, they self-renew through the return to quiescence of the cycling progeny. This mechanism, while efficient in physiological conditions does not prevent exhaustion of satellite cells in pathologies such as muscular dystrophy where numerous rounds of damage occur. Here, we describe a key role of nitric oxide, an important signaling molecule in adult skeletal muscle, on satellite cells maintenance, studied ex vivo on isolated myofibers and in vivo using the α-sarcoglycan null mouse model of dystrophy and a cardiotoxin-induced model of repetitive damage. Nitric oxide stimulated satellite cells proliferation in a pathway dependent on cGMP generation. Furthermore, it increased the number of Pax7+/Myf5− cells in a cGMP-independent pathway requiring enhanced expression of Vangl2, a member of the planar cell polarity pathway involved in the Wnt noncanonical pathway. The enhanced self-renewal ability of satellite cells induced by nitric oxide is sufficient to delay the reduction of the satellite cell pool during repetitive acute and chronic damages, favoring muscle regeneration; in the α-sarcoglycan null dystrophic mouse, it also slowed disease progression persistently. These results identify nitric oxide as a key messenger in satellite cells maintenance, expand the significance of the Vangl2-dependent Wnt noncanonical pathway in myogenesis, and indicate novel strategies to optimize nitric oxide-based therapies for muscular dystrophy.Disclosure of potential conflicts of interest is found at the end of this article.

Hereditary spastic paraparesis type 15 is a recessive complicated form of the disease clinically characterized by slowly progressive spastic paraparesis and mental deterioration with onset between the first and second decade of life. Thinning of corpus callosum is the neuroradiological distinctive sign frequently associated with white matter abnormalities. The causative gene, ZFYVE26, encodes a large protein of 2539 amino acid residues, termed spastizin, containing three recognizable domains: a zinc finger, a leucine zipper and a FYVE domain. Spastizin protein has a diffuse cytoplasmic distribution and co-localizes partially with early endosomes, the endoplasmic reticulum, microtubules and vesicles involved in protein trafficking. In addition, spastizin localizes to the mid-body during the final step of mitosis and contributes to successful cytokinesis. Spastizin interacts with Beclin 1, a protein required for cytokinesis and autophagy, which is the major lysosome-mediated degradation process in the cell. In view of the Beclin 1–spastizin interaction, we investigated the possible role of spastizin in autophagy. We carried out this analysis by using lymphoblast and fibroblast cells derived from four different spastizin mutated patients (p.I508N, p.L243P, p.R1209fsX, p.S1312X) and from control subjects. Of note, the truncating p.R1209fsX and p.S1312X mutations lead to loss of spastizin protein. The results obtained indicate that spastizin interacts with the autophagy related Beclin 1–UVRAG–Rubicon multiprotein complex and is required for autophagosome maturation. In cells lacking spastizin or with mutated forms of the protein, spastizin interaction with Beclin 1 is lost although the formation of the Beclin 1–UVRAG–Rubicon complex can still be observed. However, in these cells we demonstrate an impairment of autophagosome maturation and an accumulation of immature autophagosomes. Autophagy defects with autophagosome accumulation can be observed also in neuronal cells upon spastizin silencing. These results indicate that autophagy is a central process in the pathogenesis of complicated forms of hereditary spastic paraparesis with thin corpus callosum.

A bidirectional relationship exists between hypertension and psychiatric disorders, including unipolar and bipolar depression, anxiety, post-traumatic stress disorder (PTSD), psychosis, schizophrenia, mania, and dementia/cognitive decline. Repurposing of antihypertensive drugs to treat mental disorders is thus being explored. A systematic knowledge of the mechanisms of action and clinical consequences of the use of antihypertensive agents on neuropsychiatric functions has not been achieved yet. In this article, we review the putative role of antihypertensive agents in psychiatric disorders, discuss the targets and mechanisms of action, and examine how and to what extent specific drug classes/molecules may trigger, worsen, or mitigate psychiatric symptoms. In addition, we review pharmacokinetics (brain penetration of drugs) and pharmacogenetics data that add important information to assess risks and benefits of antihypertensive drugs in neuropsychiatric settings.The scientific literature shows robust evidence of a positive effect of α1 blockers on PTSD symptoms, nightmares and sleep quality, α2 agonists on core symptoms, executive function, and quality of life in Attention-Deficit/Hyperactivity Disorder, PTSD, Tourette’s syndrome, and β blockers on anxiety, aggression, working memory, and social communication. Renin-angiotensin system modulators exert protective effects on cognition, depression, and anxiety, and the loop diuretic bumetanide reduced the core symptoms of autism in a subset of patients. There is no evidence of clear benefits of calcium channel blockers in mood disorders in the scientific literature. These findings are mainly from preclinical studies; clinical data are still insufficient or of anecdotal nature and seldom systematic. The information herewith provided can support a better therapeutic approach to hypertension, tailored to patients with, or with high susceptibility to, psychiatric illness. It may prompt clinical studies exploring the potential benefit of antihypertensive drugs in selected patients with neuropsychiatric comorbidities that include outcomes of neuropsychiatric interest and specifically assess undesirable effects or interactions.

ZFYVE26/Spastizin and SPG11/Spatacsin encode 2 large proteins that are mutated in hereditary autosomal-recessive spastic paraplegia/paraparesis (HSP) type 15 (AR-SPG15) and type 11 (AR-SPG11), respectively. We previously have reported that AR-SPG15-related ZFYVE26 mutations lead to autophagy defects with accumulation of immature autophagosomes. ZFYVE26 and SPG11 were found to be part of a complex including the AP5 (adaptor related protein complex 5) and to have a critical role in autophagic lysosomal reformation with identification of autophagic and lysosomal defects in cells with both AR-SPG15- and AR-SPG11-related mutations. In spite of these similarities between the 2 proteins, here we report that ZFYVE26 and SPG11 are differently involved in autophagy and endocytosis. We found that both ZFYVE26 and SPG11 interact with RAB5A and RAB11, 2 proteins regulating endosome trafficking and maturation, but only ZFYVE26 mutations affected RAB protein interactions and activation. ZFYVE26 mutations lead to defects in the fusion between autophagosomes and endosomes, while SPG11 mutations do not affect this step and lead to a milder autophagy defect. We thus demonstrate that ZFYVE26 and SPG11 affect the same cellular physiological processes, albeit at different levels: both proteins have a role in autophagic lysosome reformation, but only ZFYVE26 acts at the intersection between endocytosis and autophagy, thus representing a key player in these 2 processes. Indeed expression of the constitutively active form of RAB5A in cells with AR-SPG15-related mutations partially rescues the autophagy defect. Finally the model we propose demonstrates that autophagy and the endolysosomal pathway are central processes in the pathogenesis of these complicated forms of hereditary spastic paraparesis. Abbreviations: ALR, autophagic lysosome reformation; AP5, adaptor related protein complex 5; AR, autosomal-recessive; HSP, hereditary spastic paraplegia/paraparesis; ATG14, autophagy related 14; BafA, bafilomycin A₁; BECN1, beclin 1; EBSS, Earle balanced salt solution; EEA1, early endosome antigen 1; EGF, epidermal growth factor; EGFR, epidermal growth factor receptor; GDP, guanosine diphosphate; GFP, green fluorescent protein; GTP, guanosine triphosphate; HSP, hereditary spastic paraplegias; LBPA, lysobisphosphatidic acid; MAP1LC3B/LC3B, microtubule associated protein 1 light chain 3 beta; MVBs, multivesicular bodies; PIK3C3, phosphatidylinositol 3-kinase, catalytic subunit type 3; PIK3R4, phosphoinositide-3-kinase regulatory subunit 4; PtdIns3P, phosphatidylinositol-3-phosphate; RFP, red fluorescent protein; RUBCN, RUN and cysteine rich domain containing beclin 1 interacting protein; shRNA, short hairpin RNA; SQSTM1/p62, sequestosome 1; TCC: thin corpus callosum; TF, transferrin; UVRAG, UV radiation resistance associated.