Senescent cells inhibit mouse myoblast differentiation via the SASP-lipid 15d-PGJ2 mediated modification and control of HRas.

Senescent cells are characterized by multiple features such as increased expression of senescence-associated ß-galactosidase activity (SA ß-gal) and cell cycle inhibitors such as p21 or p16. They accumulate with tissue damage and dysregulate tissue homeostasis. In the context of skeletal muscle, it is known that agents used for chemotherapy such as Doxorubicin (Doxo) cause buildup of senescent cells, leading to the inhibition of tissue regeneration. Senescent cells influence the neighboring cells via numerous secreted factors which form the senescence-associated secreted phenotype (SASP). Lipids are emerging as a key component of SASP that can control tissue homeostasis. Arachidonic acid-derived lipids have been shown to accumulate within senescent cells, specifically 15d-PGJ2, which is an electrophilic lipid produced by the non-enzymatic dehydration of the prostaglandin PGD2. This study shows that 15d-PGJ2 is also released by Doxo-induced senescent cells as an SASP factor. Treatment of skeletal muscle myoblasts with the conditioned medium from these senescent cells inhibits myoblast fusion during differentiation. Inhibition of L-PTGDS, the enzyme that synthesizes PGD2, diminishes the release of 15d-PGJ2 by senescent cells and restores muscle differentiation. We further show that this lipid post-translationally modifies Cys184 of HRas in C2C12 mouse skeletal myoblasts, causing a reduction in the localization of HRas to the Golgi, increased HRas binding to Ras Binding Domain (RBD) of RAF Kinase (RAF-RBD), and activation of cellular Mitogen Activated Protein (MAP) kinase-Extracellular Signal Regulated Kinase (Erk) signaling (but not the Akt signaling). Mutating C184 of HRas prevents the ability of 15d-PGJ2 to inhibit the differentiation of muscle cells and control the activity of HRas. This work shows that 15d-PGJ2 released from senescent cells could be targeted to restore muscle homeostasis after chemotherapy.

Metabolome profiling reveals impact of water limitation on grain filling in contrasting rice genotypes.

Drought significantly decreases crop productivity, especially in high water consuming crops like rice. Grain filling is one of the important critical growth phases in rice and drought during this phase leads to significant reduction in yield. In this study, a comparison was made between IR64 (drought susceptible) and Apo (drought tolerant) rice genotypes to capture the response to water limitation (50% field capacity (FC)) compared with the control (100%FC) during grain filling. Plants were grown in a high-throughput phenomics facility for precise imposition of moisture stress during grain filling. Apo performed better in water limited conditions with lower reduction of photosynthetic rate and maintenance of lower leaf temperature than IR64. Days from sowing to maturity, spikelet fertility and seed weight were more impeded by water limitation in IR64 than in Apo. Unlike Apo, IR64 did not show any decrease in transpiration rate at 50%FC compared with 100%FC. Metabolomic profiling of spikelets at grain filling showed distinct effects of water limitation on accumulation of metabolites, especially in Apo. Secondary metabolism, mainly the phenylpropanoid pathway involved in scavenging mechanisms, was upregulated in Apo. Accumulation of most amino acids was significantly higher in IR64 than in Apo. Due to higher rates of photosynthesis under stress, most carbohydrates accumulated more in Apo than in IR64 at 50%FC. Sucrose transporters were significantly upregulated in water limited conditions especially in Apo. Overall, thanks to higher source capacity, more source to sink transport and better scavenging, Apo showed a lower reduction in yield than IR64.

LC-HRMS based approach to identify novel sphingolipid biomarkers in breast cancer patients.

Perturbations in lipid metabolic pathways to meet the bioenergetic and biosynthetic requirements is a principal characteristic of cancer cells. Sphingolipids (SPLs) are the largest class of bioactive lipids associated to various aspects of tumorigenesis and have been extensively studied in cancer cell lines and experimental models. The clinical relevance of SPLs in human malignancies however is still poorly understood and needs further investigation. In the present study, we adopted a UHPLC-High resolution (orbitrap) Mass spectrometry (HRMS) approach to identify various sphingolipid species in breast cancer patients. A total of 49 SPLs falling into 6 subcategories have been identified. Further, integrating the multivariate analysis with metabolomics enabled us to identify an elevation in the levels of ceramide phosphates and sphingosine phosphates in tumor tissues as compared to adjacent normal tissues. The expression of genes involved in the synthesis of reported metabolites was also determined in local as well as TCGA cohort. A significant upregulation in the expression of CERK and SPHK1 was observed in tumor tissues in local and TCGA cohort. Sphingomyelin levels were found to be high in adjacent normal tissues. Consistent with the above findings, expression of SGMS1 in tumor tissues was downregulated in TCGA cohort only. Clinical correlations of the selected metabolites and their performance as biomarkers was also evaluated. Significant ROC and positive correlation with Ki67 index highlight the diagnostic potential and clinical relevance of ceramide phosphates in breast cancer.