Glycerophosphodiesterase 3 (GDE3) is a lysophosphatidylinositol-specific ectophospholipase C acting as an endocannabinoid signaling switch.

Endocannabinoid signaling plays a regulatory role in various (neuro)biological functions. 2-arachidonoylglycerol (2-AG) is the most abundant endocannabinoid, and although its canonical biosynthetic pathway involving phosphoinositide-specific phospholipase C and diacylglycerol lipase α is known, alternative pathways remain unsettled. Here, we characterize a noncanonical pathway implicating glycerophosphodiesterase 3 (GDE3, from GDPD2 gene). Human GDE3 expressed in HEK293T cell membranes catalyzed the conversion of lysophosphatidylinositol (LPI) into monoacylglycerol and inositol-1-phosphate. The enzyme was equally active against 1-acyl and 2-acyl LPI. When using 2-acyl LPI, where arachidonic acid is the predominant fatty acid, LC-MS analysis identified 2-AG as the main product of LPI hydrolysis by GDE3. Furthermore, inositol-1-phosphate release into the medium occurred upon addition of LPI to intact cells, suggesting that GDE3 is actually an ecto-lysophospholipase C. In cells expressing G-protein-coupled receptor GPR55, GDE3 abolished 1-acyl LPI-induced signaling. In contrast, upon simultaneous ex-pression of GDE3 and cannabinoid receptor CB2, 2-acyl LPI evoked the same signal as that induced by 2-AG. These data strongly suggest that, in addition to degrading the GPR55 LPI ligand, GDE3 can act as a switch between GPR55 and CB2 signaling. Coincident with a major expression of both GDE3 and CB2 in the spleen, spleens from transgenic mice lacking GDE3 displayed doubling of LPI content compared with WT mice. Decreased production of 2-AG in whole spleen was also observed, supporting the in vivo relevance of our findings. These data thus open a new research avenue in the field of endocannabinoid generation and reinforce the view of GPR55 and LPI being genuine actors of the endocannabinoid system.

Noonan syndrome-causing SHP2 mutants impair ERK-dependent chondrocyte differentiation during endochondral bone growth.

Growth retardation is a constant feature of Noonan syndrome (NS) but its physiopathology remains poorly understood. We previously reported that hyperactive NS-causing SHP2 mutants impair the systemic production of insulin-like growth factor 1 (IGF1) through hyperactivation of the RAS/extracellular signal-regulated kinases (ERK) signalling pathway. Besides endocrine defects, a direct effect of these mutants on growth plate has not been explored, although recent studies have revealed an important physiological role for SHP2 in endochondral bone growth. We demonstrated that growth plate length was reduced in NS mice, mostly due to a shortening of the hypertrophic zone and to a lesser extent of the proliferating zone. These histological features were correlated with decreased expression of early chondrocyte differentiation markers, and with reduced alkaline phosphatase staining and activity, in NS murine primary chondrocytes. Although IGF1 treatment improved growth of NS mice, it did not fully reverse growth plate abnormalities, notably the decreased hypertrophic zone. In contrast, we documented a role of RAS/ERK hyperactivation at the growth plate level since 1) NS-causing SHP2 mutants enhance RAS/ERK activation in chondrocytes in vivo (NS mice) and in vitro (ATDC5 cells) and 2) inhibition of RAS/ERK hyperactivation by U0126 treatment alleviated growth plate abnormalities and enhanced chondrocyte differentiation. Similar effects were obtained by chronic treatment of NS mice with statins. In conclusion, we demonstrated that hyperactive NS-causing SHP2 mutants impair chondrocyte differentiation during endochondral bone growth through a local hyperactivation of the RAS/ERK signalling pathway, and that statin treatment may be a possible therapeutic approach in NS.

SHP2 drives inflammation-triggered insulin resistance by reshaping tissue macrophage populations.

Insulin resistance is a key event in type 2 diabetes onset and a major comorbidity of obesity. It results from a combination of fat excess-triggered defects, including lipotoxicity and metaflammation, but the causal mechanisms remain difficult to identify. Here, we report that hyperactivation of the tyrosine phosphatase SHP2 found in Noonan syndrome (NS) led to an unsuspected insulin resistance profile uncoupled from altered lipid management (for example, obesity or ectopic lipid deposits) in both patients and mice. Functional exploration of an NS mouse model revealed this insulin resistance phenotype correlated with constitutive inflammation of tissues involved in the regulation of glucose metabolism. Bone marrow transplantation and macrophage depletion improved glucose homeostasis and decreased metaflammation in the mice, highlighting a key role of macrophages. In-depth analysis of bone marrow-derived macrophages in vitro and liver macrophages showed that hyperactive SHP2 promoted a proinflammatory phenotype, modified resident macrophage homeostasis, and triggered monocyte infiltration. Consistent with a role of SHP2 in promoting inflammation-driven insulin resistance, pharmaceutical SHP2 inhibition in obese diabetic mice improved insulin sensitivity even better than conventional antidiabetic molecules by specifically reducing metaflammation and alleviating macrophage activation. Together, these results reveal that SHP2 hyperactivation leads to inflammation-triggered metabolic impairments and highlight the therapeutical potential of SHP2 inhibition to ameliorate insulin resistance.

Ghrelin uses the GHS-R1a/Gi/cAMP pathway and induces differentiation only in mature osteoblasts. This ghrelin pathway is impaired in AIS patients.

We have examined the Acylated Ghrelin (AG)/Gi pathway in different human osteoblastic cell lines. We have found that: 1) AG induces differentiation/mineralization only in mature osteoblasts; 2) the expression of GHS-R1a increases up to the mature cell stage, 3) the action is mediated via the GHS-R/Gi/cAMP pathway only in mature osteoblasts, and 4) osteoblastic cells from adolescent idiopathic scoliosis (AIS) are resistant to the AG/Gi/cAMP pathway. Altogether, these results suggested that AG uses the GHS-R1a/Gi/cAMP pathway to induce differentiation in mature osteoblasts only. This pathway is impaired in AIS osteoblasts. Understanding AG-specific pathways involved in normal and pathological osteoblasts may be useful for developing new treatments for pathologies such as AIS or osteoporosis.

Expression of the type 1 lysophosphatidic acid receptor in osteoblastic cell lineage controls both bone mineralization and osteocyte specification.

Lysphosphatidic acid (LPA) is a major natural bioactive lipid mediator whose biological functions affect multiple organs. These include bone as demonstrated by global Lpar1-knockout mice (Lpar1-/-) which present a bone growth defect. LPA acts on all bone cells including osteoblasts, that are responsible for bone formation, and osteoclasts, which are specialized cells that resorb bone. LPA appears as a potential new coupling molecule during bone remodeling. LPA1 is the most ubiquitous LPA receptor among the six LPA receptor family members (LPA1-6). To better understand the specific role of LPA via its receptor LPA1 in osteoblastic cell lineage we generated osteoblast-specific Lpar1 knockout mice (Lpar1-∆Ob) by crossing Lpar1flox/flox and Osx:Cre+ mouse lines. Lpar1-∆Ob mice do not recapitulate the bone defects of Lpar1-/- mice but revealed reduced bone mineralization and decreased cortical thickness, as well as increased bone porosity associated with an augmentation in the lacunae areas of osteocyte and their apoptotic yield. In vitro, primary Lpar1-∆Ob and immortalized cl1-Ob-Lpar1-/- osteoblasts revealed a remarkable premature expression of alkaline phosphatase, reduced cell proliferation associated with decreased YAP-P nuclear accumulation, and reduced mineralization activity. Osteocyte specification is markedly impaired as demonstrated by reduced expression of early (E11) and late (DMP1, DKK1, SOST) osteocyte markers ex vivo in enriched osteocytic fractions of Lpar1-∆Ob mouse bone explants. In addition, E11 expression and dendrite formation induced by FGF2 are markedly impaired in both primary Lpar1-∆Ob and immortalized cl1-Ob-Lpar1-/- osteoblasts. Taken together these results suggest a new role for LPA in bone mass control via bone mineralization and osteocyte function.

Biodistribution and Biosafety of a Poly(Phosphorhydrazone) Dendrimer, an Anti-Inflammatory Drug-Candidate.

Dendrimers are nanosized, arborescent polymers of which size and structure are perfectly controlled. This is one reason why they are widely used for biomedical purposes. Previously, we showed that a phosphorus-based dendrimer capped with anionic azabisphosphonate groups (so-called ABP dendrimer) has immuno-modulatory and anti-inflammatory properties towards human immune cells in vitro. Thereafter, we have shown that the ABP dendrimer has a promising therapeutic efficacy to treat models of chronic inflammatory disorders. On the way to clinical translation, the biodistribution and the safety of this drug-candidate has to be thoroughly assessed. In this article, we present preliminary non-clinical data regarding biodistribution, hematological safety, genotoxicity, maximal tolerated doses, and early cardiac safety of the ABP dendrimer. One of the genotoxicity assays reveals a potential mutagen effect of the item at a concentration above 200 µM, i.e., up to 100 times the active dose in vitro on human immune cells. However, as the results obtained for all the other assays show that the ABP dendrimer has promising biodistribution and safety profiles, there is no red flag raised to hamper the regulatory pre-clinical development of the ABP dendrimer.

Endospanin-2 enhances skeletal muscle energy metabolism and running endurance capacity.

Metabolic stresses such as dietary energy restriction or physical activity exert beneficial metabolic effects. In the liver, endospanin-1 and endospanin-2 cooperatively modulate calorie restriction-mediated (CR-mediated) liver adaptations by controlling growth hormone sensitivity. Since we found CR to induce endospanin protein expression in skeletal muscle, we investigated their role in this tissue. In vivo and in vitro endospanin-2 triggers ERK phosphorylation in skeletal muscle through an autophagy-dependent pathway. Furthermore, endospanin-2, but not endospanin-1, overexpression decreases muscle mitochondrial ROS production, induces fast-to-slow fiber-type switch, increases skeletal muscle glycogen content, and improves glucose homeostasis, ultimately promoting running endurance capacity. In line, endospanin-2-/- mice display higher lipid peroxidation levels, increased mitochondrial ROS production under mitochondrial stress, decreased ERK phosphorylation, and reduced endurance capacity. In conclusion, our results identify endospanin-2 as a potentially novel player in skeletal muscle metabolism, plasticity, and function.

Absence of the lysophosphatidic acid receptor LPA1 results in abnormal bone development and decreased bone mass.

Lysophosphatidic acid (LPA) is a lipid mediator that acts in paracrine systems via interaction with a subset of G protein-coupled receptors (GPCRs). LPA promotes cell growth and differentiation, and has been shown to be implicated in a variety of developmental and pathophysiological processes. At least 6 LPA GPCRs have been identified to date: LPA1-LPA6. Several studies have suggested that local production of LPA by tissues and cells contributes to paracrine regulation, and a complex interplay between LPA and its receptors, LPA1 and LPA4, is believed to be involved in the regulation of bone cell activity. In particular, LPA1 may activate both osteoblasts and osteoclasts. However, its role has not as yet been examined with regard to the overall status of bone in vivo. We attempted to clarify this role by defining the bone phenotype of LPA1((-/-)) mice. These mice demonstrated significant bone defects and low bone mass, indicating that LPA1 plays an important role in osteogenesis. The LPA1((-/-)) mice also presented growth and sternal and costal abnormalities, which highlights the specific roles of LPA1 during bone development. Microcomputed tomography and histological analysis demonstrated osteoporosis in the trabecular and cortical bone of LPA1((-/-)) mice. Finally, bone marrow mesenchymal progenitors from these mice displayed decreased osteoblastic differentiation. These results suggest that LPA1 strongly influences bone development both qualitatively and quantitatively and that, in vivo, its absence results in decreased osteogenesis with no clear modification of osteoclasis. They open perspectives for a better understanding of the role of the LPA/LPA1 paracrine pathway in bone pathophysiology.