Nuclear lipidome is altered in amyotrophic lateral sclerosis: A pilot study

Nucleocytosolic transport, a membrane process, is impaired in motor neurons in amyotrophic lateral sclerosis (ALS). This study analyzes the nuclear lipidome in motor neurons in ALS and examines molecular pathways linked to the major lipid alterations. Nuclei were obtained from the frozen anterior horn of the lumbar spinal cord of ALS patients and age-matched controls. Lipidomic profiles of this subcellular fraction were obtained using liquid chromatography and mass spectrometry. We validated the mechanisms behind presumable lipidomic changes by exploring ALS surrogate models including human motor neurons (derived from ALS lines and controls) subjected to oxidative stress, the hSOD-G93A transgenic mice, and samples from an independent cohort of ALS patients. Among the differential lipid species, we noted 41 potential identities, mostly belonging to phospholipids (particularly ether phospholipids, as plasmalogens), as well as diacylglycerols and triacylglycerides. Decreased expression of alkyldihydroxyacetonephosphate synthase (AGPS)-a critical peroxisomal enzyme in plasmalogen synthesis-is found in motor neuron disease models; this occurs in parallel with an increase in the expression of sterol carrier protein 2 (SCP2) mRNA in ALS and Scp2 levels in G93A transgenic mice. Further, we identified diminished expression of diacylglycerol-related enzymes, such as phospholipase C βI (PLCβI) and protein kinase CβII (PKCβII), linked to diacylglycerol metabolism. Finally, lipid droplets were recognized in the nuclei, supporting the identification of triacylglycerides as differential lipids. Our results point to the potentially pathogenic role of altered composition of nuclear membrane lipids and lipids in the nucleoplasm in the anterior horn of the spinal cord in ALS. Overall, these data support the usefulness of subcellular lipidomics applied to neurodegenerative diseases.

Arabidopsis AtPLC2 Is a Primary Phosphoinositide-Specific Phospholipase C in Phosphoinositide Metabolism and the Endoplasmic Reticulum Stress Response

Phosphoinositides represent important lipid signals in the plant development and stress response. However, multiple isoforms of the phosphoinositide biosynthetic genes hamper our understanding of the pivotal enzymes in each step of the pathway as well as their roles in plant growth and development. Here, we report that phosphoinositide-specific phospholipase C2 (AtPLC2) is the primary phospholipase in phosphoinositide metabolism and is involved in seedling growth and the endoplasmic reticulum (ER) stress responses in Arabidopsis thaliana. Lipidomic profiling of multiple plc mutants showed that the plc2-1 mutant increased levels of its substrates phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate, suggesting that the major phosphoinositide metabolic pathway is impaired. AtPLC2 displayed a distinct tissue expression pattern and localized at the plasma membrane in different cell types, where phosphoinositide signaling occurs. The seedlings of plc2-1 mutant showed growth defect that was complemented by heterologous expression of AtPLC2, suggesting that phosphoinositide-specific phospholipase C activity borne by AtPLC2 is required for seedling growth. Moreover, the plc2-1 mutant showed hypersensitive response to ER stress as evidenced by changes in relevant phenotypes and gene expression profiles. Our results revealed the primary enzyme in phosphoinositide metabolism, its involvement in seedling growth and an emerging link between phosphoinositide and the ER stress response.

Hypobaric Preconditioning Modifies Group I mGluRs Signaling in Brain Cortex

The study assessed involvement of Ca(2+) signaling mediated by the metabotropic glutamate receptors mGluR1/5 in brain tolerance induced by hypoxic preconditioning. Acute slices of rat piriform cortex were tested 1 day after exposure of adult rats to mild hypobaric hypoxia for 2 h at a pressure of 480 hPa once a day for three consecutive days. We detected 44.1 ± 11.6 % suppression of in vitro anoxia-induced increases of intracellular Ca(2+) levels and a fivefold increase in Ca(2+) transients evoked by selective mGluR1/5 agonist, DHPG. Western blot analysis of cortical homogenates demonstrated a 11 ± 4 % decrease in mGluR1 immunoreactivity (IR), and in the nuclei-enriched fraction a 12 ± 3 % increase in IR of phospholipase Cβ1 (PLCβ1), which is a major mediator of mGluR1/5 signaling. Immunocytochemical analysis of the cortex revealed increase in the mGluR1/5 and PLCβ1 IR in perikarya, and a decrease in IR of the neuronal inositol trisphosphate receptors (IP3Rs). We suggest that enhanced expression of mGluR5 and PLCβ1 and potentiation of Ca(2+) signaling may represent pro-survival upregulation of Ca(2+)-dependent genomic processes, while decrease in mGluR1 and IP3R IR may be attributed to a feedback mechanism preventing excessive intracellular Ca(2+) release.

PI-PLCβ1b affects Akt activation, cyclin E expression, and caspase cleavage, promoting cell survival in pro-B-lymphoblastic cells exposed to oxidative stress

The phosphoinositide-dependent signal transduction pathway has been implicated in the control of a variety of biologic processes, such as the regulation of cellular metabolism and homeostasis, cell proliferation and differentiation, and apoptosis. One of the key players in the regulation of inositol lipid signaling is the phospholipase Cβ1 (PI-PLCβ1), that hydrolyzes phosphatidylinositol 4,5-bisphosphate [PtIns(4,5)P2], giving rise to the second messengers inositol triphosphate and diacylglicerol. PI-PLCβ1 has been associated with the regulation of several cellular functions, some of which have not yet been fully understood. In particular, it has been reported that PI-PLCβ1 protects murine fibroblasts from oxidative stress-induced cell death. The mediators of oxidative stress, reactive oxygen species (ROS), have been shown to regulate major epigenetic processes, causing the silencing of tumor suppressors and enhancing the proliferation of leukemic cells under oxidative stress. Investigation of the interplay between ROS, PI-PLCβ1, and their signaling mediators in leukemia might therefore reveal innovative targets of pharmacological therapy in the treatment for leukemia. In this work, we demonstrate that in pro-B-lymphoblastic cells (Ba/F3), treated with H2O2, PI-PLCβ1b conferred resistance to cell death, promoting cell cycle progression and cell proliferation and influencing the expression of cyclin A and E. Interestingly, we found that, expression of PI-PLCβ1b affects the activity of caspase-3, caspase-7, and of several protein kinases induced by oxidative stress. In particular, PI-PLCβ1b expression completely abolished the phosphorylation of Erk1/2 MAP kinases, down-regulated phosphatase and tensin homolog (PTEN), and up-regulated the phosphorylation of Akt, thereby sustaining cellular proliferation.

Fluid flow-induced calcium response in osteoclasts: signaling pathways

Intracellular calcium oscillation and its downstream signaling in osteoclasts is believed to play critical roles in regulating bone resorption. Our previous study demonstrated that fluid shear stress (FSS) induced more calcium responsive peaks in the late differentiated osteoclasts than the early ones. In this paper, the signaling pathways of FSS-induced calcium response for the osteoclasts in different differentiation stages were studied. RAW264.7 macrophage cells were induced to differentiate into osteoclasts with the conditioned medium from MC3T3-E1 osteoblasts. Furthermore pharmacological agents were added to block the specific signaling pathways. Finally the cells were exposed to FSS at different levels (1 or 10 dyne/cm(2)) after being induced for 4 or 8 days. The results showed that the mechanosensitive, cation-selective channels, phospholipase C (PLC) and endoplasmic reticulum constituted the major signaling pathway for mechanical stimulation-induced calcium response in osteoclasts. Extracellular calcium or ATP involved with calcium oscillation in a FSS magnitude-dependent manner. This pathway study may help to give insight into the molecular mechanism of mechanical stimulation-regulated bone remodeling.