A substantial amount of mitochondrial energy is required for cell-cycle progression. The mechanisms underlying the coordination of the mitochondrial respiration with cell-cycle progression, ...especially the G2/M transition, remain to be elucidated. Here, we show that a fraction of cyclin B1/Cdk1 proteins localizes to the matrix of mitochondria and phosphorylates a cluster of mitochondrial proteins, including the complex I (CI) subunits in the respiratory chain. Cyclin B1/Cdk1-mediated CI phosphorylation enhances CI activity, whereas deficiency of such phosphorylation in each of the relevant CI subunits results in impairment of CI function. Mitochondria-targeted cyclin B1/Cdk1 increases mitochondrial respiration with enhanced oxygen consumption and ATP generation, which provides cells with efficient bioenergy for G2/M transition and shortens overall cell-cycle time. Thus, cyclin B1/Cdk1-mediated phosphorylation of mitochondrial substrates allows cells to sense and respond to increased energy demand for G2/M transition and, subsequently, to upregulate mitochondrial respiration for successful cell-cycle progression.
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•A fraction of cyclin B1/Cdk1 proteins localizes to mitochondria at G2/M transition•A cluster of mitochondrial proteins is phosphorylated by cyclin B1/Cdk1•Cyclin B1/Cdk1 phosphorylates CI to boost mitochondrial ATP generation•Cyclin B1/Cdk1 regulates mitochondria metabolism to coordinate G2/M progression
Wang et al. find that cyclin B1/Cdk1 localizes to the mitochondrial matrix and phosphorylates complex I to boost mitochondrial respiration and ATP generation during G2/M. Mitochondrial cyclin B1/Cdk1 thus enables cell-cycle regulation of mitochondrial respiration to serve the increased cellular energy demand of the G2/M transition.
G-protein-coupled receptors (GPCRs) are known to possess two different conformations, active and inactive, and they spontaneously alternate between the two in the absence of ligands. Here, we ...analyzed the agonist-independent GPCR activity for its possible role in receptor-instructed axonal projection. We generated transgenic mice expressing activity mutants of the β2-adrenergic receptor, a well-characterized GPCR with the highest homology to odorant receptors (ORs). We found that mutants with altered agonist-independent activity changed the transcription levels of axon-targeting molecules—e.g., Neuropilin-1 and Plexin-A1—but not of glomerular segregation molecules—e.g., Kirrel2 and Kirrel3—thus causing shifts in glomerular locations along the anterior-posterior (A-P) axis. Knockout and in vitro experiments demonstrated that Gs, but not Golf, is responsible for mediating the agonist-independent GPCR activity. We conclude that the equilibrium of conformational transitions set by each OR is the major determinant of expression levels of A-P-targeting molecules.
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•Agonist-independent GPCR activity regulates A-P targeting of OSN axons•Receptor mutants with altered baseline activity caused shifts in glomerular locations•A stimulatory G protein (Gs), but not Golf, mediates the OR baseline activity•This is a demonstration of in vivo function of GPCR basal activity during development
The level of agonist-independent activity of a given olfactory receptor is the major determinant of the expression levels of the anterior-posterior targeting molecules that control axon guidance of olfactory sensory neurons.
Hypertension is a primary risk factor for cardiovascular diseases including myocardial infarction and stroke. Major determinants of blood pressure are vasodilatory factors such as nitric oxide (NO) ...released from the endothelium under the influence of fluid shear stress exerted by the flowing blood. Several endothelial signaling processes mediating fluid shear stress-induced formation and release of vasodilatory factors have been described. It is, however, still poorly understood how fluid shear stress induces these endothelial responses. Here we show that the endothelial mechanosensitive cation channel PIEZO1 mediated fluid shear stress-induced release of adrenomedullin, which in turn activated its Gs-coupled receptor. The subsequent increase in cAMP levels promoted the phosphorylation of endothelial NO synthase (eNOS) at serine 633 through protein kinase A (PKA), leading to the activation of the enzyme. This Gs/PKA-mediated pathway synergized with the AKT-mediated pathways leading to eNOS phosphorylation at serine 1177. Mice with endothelium-specific deficiency of adrenomedullin, the adrenomedullin receptor, or Gαs showed reduced flow-induced eNOS activation and vasodilation and developed hypertension. Our data identify fluid shear stress-induced PIEZO1 activation as a central regulator of endothelial adrenomedullin release and establish the adrenomedullin receptor and subsequent Gs-mediated formation of cAMP as a critical endothelial mechanosignaling pathway regulating basal endothelial NO formation, vascular tone, and blood pressure.
Adipocytes deficient in fatty acid synthase (iAdFASNKO) emit signals that mimic cold exposure to enhance the appearance of thermogenic beige adipocytes in mouse inguinal white adipose tissues ...(iWATs). Both cold exposure and iAdFASNKO upregulate the sympathetic nerve fiber (SNF) modulator Neuregulin 4 (Nrg4), activate SNFs, and require adipocyte cyclic AMP/protein kinase A (cAMP/PKA) signaling for beige adipocyte appearance, as it is blocked by adipocyte Gsα deficiency. Surprisingly, however, in contrast to cold-exposed mice, neither iWAT denervation nor Nrg4 loss attenuated adipocyte browning in iAdFASNKO mice. Single-cell transcriptomic analysis of iWAT stromal cells revealed increased macrophages displaying gene expression signatures of the alternately activated type in iAdFASNKO mice, and their depletion abrogated iWAT beiging. Altogether, these findings reveal that divergent cellular pathways are sufficient to cause adipocyte browning. Importantly, adipocyte signaling to enhance alternatively activated macrophages in iAdFASNKO mice is associated with enhanced adipose thermogenesis independent of the sympathetic neuron involvement this process requires in the cold.
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•Light sheet microscopy reveals nerve fibers abutting beige adipocytes in iWAT•iWAT denervation blocks cold-induced but not adipocyte FASNKO-induced iWAT beiging•cAMP/PKA pathway in adipocytes mediates iWAT beiging in adipocyte FASNKO mice•Macrophages but not innervation are required for beiging in adipocyte FASNKO mice
Henriques et al. show an alternative pathway to enhance thermogenesis through an adipocyte cAMP/PKA axis in denervated iWAT. Signals emanating from this pathway generate M2-type macrophages associated with iWAT browning.
Fibrous dysplasia (FD) is a focal bone lesion composed of immature mesenchymal osteoblastic precursor cells. Some FD patients also have hyperpigmented skin lesions (café‐au‐lait spots), ...gonadotropin‐independent sexual precocity, and/or other endocrine and nonendocrine manifestations (McCune‐Albright syndrome MAS). MAS results from somatic mutations occurring during early development, resulting in a widespread mosaic of normal and mutant‐bearing cells, which predicts that the clinical presentation of each patient is determined by the extent and distribution of abnormal cells. These mutations encode constitutively active forms of Gsα, the ubiquitously expressed G protein α‐subunit that couples hormone receptors to intracellular cAMP generation. These mutations lead to substitution of amino acid residues that are critical for the intrinsic GTPase activity that is normally required to deactivate the G protein. This leads to prolonged activation of Gsα and its downstream effectors even with minimal receptor activation. This explains why MAS patients have stimulation of multiple peripheral endocrine glands in the absence of circulating stimulatory pituitary hormones and increased skin pigment, which is normally induced by melanocyte‐stimulating hormone through Gsα/cAMP. Similar mutations are also present in 40% of pituitary tumors in acromegaly patients and less commonly in other endocrine tumors. FD results from increased cAMP in bone marrow stromal cells, leading to increased proliferation and abnormal differentiation. Parental origin of the mutated allele may also affect the clinical presentation, because Gsα is imprinted and expressed only from the maternal allele in some tissues (e.g., pituitary somatotrophs).
Heterotopic ossification, the pathologic formation of extraskeletal bone, occurs as a common complication of trauma or in genetic disorders and can be disabling and lethal. However, the underlying ...molecular mechanisms are largely unknown. Here we demonstrate that Gαs restricts bone formation to the skeleton by inhibiting Hedgehog signaling in mesenchymal progenitor cells. In progressive osseous heteroplasia, a human disease caused by null mutations in GNAS, which encodes Gαs, Hedgehog signaling is upregulated in ectopic osteoblasts and progenitor cells. In animal models, we show that genetically-mediated ectopic Hedgehog signaling is sufficient to induce heterotopic ossification, whereas inhibition of this signaling pathway by genetic or pharmacological means strongly reduces the severity of this condition. As our previous work has shown that GNAS gain-of-function mutations upregulate WNT-β-catenin signaling in osteoblast progenitor cells, resulting in their defective differentiation and fibrous dysplasia, we identify Gαs as a key regulator of proper osteoblast differentiation through its maintenance of a balance between the Wnt-β-catenin and Hedgehog pathways. Also, given the results here of the pharmacological studies in our mouse model, we propose that Hedgehog inhibitors currently used in the clinic for other conditions, such as cancer, may possibly be repurposed for treating heterotopic ossification and other diseases caused by GNAS inactivation.
Genomic alterations in GNAS, the gene coding for the Gαs heterotrimeric G protein, are associated with a large number of human diseases. Here, we explored the role of Gαs on stem cell fate decisions ...by using the mouse epidermis as a model system. Conditional epidermal deletion of Gnas or repression of PKA signalling caused a remarkable expansion of the stem cell compartment, resulting in rapid basal-cell carcinoma formation. In contrast, inducible expression of active Gαs in the epidermis caused hair follicle stem cell exhaustion and hair loss. Mechanistically, we found that Gαs-PKA disruption promotes the cell autonomous Sonic Hedgehog pathway stimulation and Hippo signalling inhibition, resulting in the non-canonical activation of GLI and YAP1. Our study highlights an important tumour suppressive function of Gαs-PKA, limiting the proliferation of epithelial stem cells and maintaining proper hair follicle homeostasis. These findings could have broad implications in multiple pathophysiological conditions, including cancer.
A physical examination was unremarkable, but laboratory investigations showed hypercalcaemia with a calcium concentration of 3·18 mmol/L (normal 2·15–2·55) and an elevated parathyroid hormone (PTH) ...concentration of 323·7 pg/mL (normal 10·0–65·0). The x-ray findings described in this case are similar to patients with other conditions with either elevated PTH or cAMP signalling: firstly, pseudohypoparathyroidism (figure; appendix)—where renal PTH resistance at the kidney, but not the bone, leads to compensatory elevated PTH blood levels; secondly, treatment of hypoparathyroidism with pharmacologic doses of PTH (figure; appendix); and finally, fibrous dysplasia—which is caused by gain-of-function mutations in the Gαs protein immediately downstream of PTH and associated with increased intracellular cAMP signalling (figure; appendix). Declaration of interests This research was made possible by the NIH Medical Research Scholars Program, a public-private partnership supported jointly by the NIH and contributions to the Foundation for the NIH from the Doris Duke Charitable Foundation, Genentech, the American Association for Dental Research, and the Colgate-Palmolive Company.
Activation of the sympathetic nervous system causes pronounced metabolic changes that are mediated by multiple adrenergic receptor subtypes. Systemic treatment with β
adrenergic receptor agonists ...results in multiple beneficial metabolic effects, including improved glucose homeostasis. To elucidate the underlying cellular and molecular mechanisms, we chronically treated wild-type mice and several newly developed mutant mouse strains with clenbuterol, a selective β
-adrenergic receptor agonist. Clenbuterol administration caused pronounced improvements in glucose homeostasis and prevented the metabolic deficits in mouse models of β-cell dysfunction and insulin resistance. Studies with skeletal muscle-specific mutant mice demonstrated that these metabolic improvements required activation of skeletal muscle β
-adrenergic receptors and the stimulatory G protein, G
. Unbiased transcriptomic and metabolomic analyses showed that chronic β
-adrenergic receptor stimulation caused metabolic reprogramming of skeletal muscle characterized by enhanced glucose utilization. These findings strongly suggest that agents targeting skeletal muscle metabolism by modulating β
-adrenergic receptor-dependent signaling pathways may prove beneficial as antidiabetic drugs.
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