Lipid desaturation regulates the balance between self-renewal and differentiation in mouse blastocyst-derived stem cells.

Stem cells are defined by their ability to self-renew and differentiate, both shown in multiple studies to be regulated by metabolic processes. To decipher metabolic signatures of self-renewal in blastocyst-derived stem cells, we compared early differentiating embryonic stem cells (ESCs) and their extra-embryonic counterparts, trophoblast (T)SCs to their self-renewing counterparts. A metabolomics analysis pointed to the desaturation of fatty acyl chains as a metabolic signature of differentiating blastocyst-derived SCs via the upregulation of delta-6 desaturase (D6D; FADS2) and delta-5 desaturase (D5D; FADS1), key enzymes in the biosynthesis of polyunsaturated fatty acids (PUFAs). The inhibition of D6D or D5D by specific inhibitors or SiRNA retained stemness in ESCs and TSCs, and attenuated endoplasmic reticulum (ER) stress-related apoptosis. D6D inhibition in ESCs upregulated stearoyl-CoA desaturase-1 (Scd1), essential to maintain ER homeostasis. In TSCs, however, D6D inhibition downregulated Scd1. TSCs show higher Scd1 mRNA expression and high levels of monounsaturated fatty acyl chain products in comparison to ESCs. The addition of oleic acid, the product of Scd1 (essential for ESCs), to culture medium, was detrimental to TSCs. Interestingly, TSCs express a high molecular mass variant of Scd1 protein, hardly expressed by ESCs. Taken together, our data suggest that lipid desaturation is a metabolic regulator of the balance between differentiation and self-renewal of ESCs and TSCs. They point to lipid polydesaturation as a driver of differentiation in both cell types. Monounsaturated fatty acids (MUFAs), essential for ESCs are detrimental to TSCs.

A negative feedback loop of TOR signaling balances growth and stress-response trade-offs in plants.

TOR kinase is a central coordinator of nutrient-dependent growth in eukaryotes. Maintaining optimal TOR signaling is critical for the normal development of organisms. In this study, we describe a negative feedback loop of TOR signaling helping in the adaptability of plants in changing environmental conditions. Using an interdisciplinary approach, we show that the plant-specific zinc finger protein FLZ8 acts as a regulator of TOR signaling in Arabidopsis. In sugar sufficiency, TOR-dependent and -independent histone modifications upregulate the expression of FLZ8. FLZ8 negatively regulates TOR signaling by promoting antagonistic SnRK1α1 signaling and bridging the interaction of SnRK1α1 with RAPTOR1B, a crucial accessory protein of TOR. This negative feedback loop moderates the TOR-growth signaling axis in the favorable condition and helps in the activation of stress signaling in unfavorable conditions, establishing its importance in the adaptability of plants.

Activation of the Type III Secretion System of Enteropathogenic Escherichia coli Leads to Remodeling of Its Membrane Composition and Function.

The cell envelope of Gram-negative bacteria is a complex structure, essential for bacterial survival and for resistance to many antibiotics. Channels that cross the bacterial envelope and the host cell membrane form secretion systems that are activated upon attachment to host, enabling bacteria to inject effector molecules into the host cell, required for bacterium-host interaction. The type III secretion system (T3SS) is critical for the virulence of several pathogenic bacteria, including enteropathogenic Escherichia coli (EPEC). EPEC T3SS activation is associated with repression of carbon storage regulator (CsrA), resulting in gene expression remodeling, which is known to affect EPEC central carbon metabolism and contributes to the adaptation to a cell-adherent lifestyle in a poorly understood manner. We reasoned that the changes in the bacterial envelope upon attachment to the host and the activation of a secretion system may involve a modification of the lipid composition of bacterial envelope. Accordingly, we performed a lipidomics analysis on mutant strains that simulate T3SS activation. We saw a shift in glycerophospholipid metabolism toward the formation of lysophospholipids, attributed to corresponding upregulation of the phospholipase gene pldA and the acyltransferase gene ygiH upon T3SS activation in EPEC. We also detected a shift from menaquinones and ubiquinones to undecaprenyl lipids, concomitant with abnormal synthesis of O antigen. The remodeling of lipid metabolism is mediated by CsrA and associated with increased bacterial cell size and zeta potential and a corresponding alteration in EPEC permeability to vancomycin, increasing the sensitivity of T3SS-activated strains and of adherent wild-type EPEC to the antibiotic. IMPORTANCE The characterization of EPEC membrane lipid metabolism upon attachment to the host is an important step toward a better understanding the shift of EPEC, a notable human pathogen, from a planktonic to adherent lifestyle. It may also apply to other pathogenic bacteria that use this secretion system. We predict that upon attachment to host cells, the lipid remodeling upon T3SS activation contributes to bacterial fitness and promotes host colonization, and we show that it is associated with increased cell permeability and higher sensitivity to vancomycin. To the best of our knowledge, this is the first demonstration of a bacterial lipid remodeling due to activation of a secretion system.

Distinct infrastructure of lipid networks in visceral and subcutaneous adipose tissues in overweight humans.

BACKGROUND: Adipose tissue plays important roles in health and disease. Given the unique association of visceral adipose tissue with obesity-related metabolic diseases, the distribution of lipids between the major fat depots located in subcutaneous and visceral regions may shed new light on adipose tissue-specific roles in systemic metabolic perturbations. OBJECTIVE: We sought to characterize the lipid networks and unveil differences in the metabolic infrastructure of the 2 adipose tissues that may have functional and nutritional implications. METHODS: Paired visceral and subcutaneous adipose tissue samples were obtained from 17 overweight patients undergoing elective abdominal surgery. Ultra-performance LC-MS was used to measure 18,640 adipose-derived features; 520 were putatively identified. A stem cell model for adipogenesis was used to study the functional implications of the differences found. RESULTS: Our analyses resulted in detailed lipid metabolic maps of the 2 major adipose tissues. They point to a higher accumulation of phosphatidylcholines, triacylglycerols, and diacylglycerols, although lower ceramide concentrations, in subcutaneous tissue. The degree of unsaturation was lower in visceral adipose tissue (VAT) phospholipids, indicating lower unsaturated fatty acid incorporation into adipose tissue. The differential abundance of phosphatidylcholines we found can be attributed at least partially to higher expression of phosphatidylethanolamine methyl transferase (PEMT). PEMT-deficient embryonic stem cells showed a dramatic decrease in adipogenesis, and the resulting adipocytes exhibited lower accumulation of lipid droplets, in line with the lower concentrations of glycerolipids in VAT. Ceramides may inhibit the expression of PEMT by increased insulin resistance, thus potentially suggesting a functional pathway that integrates ceramide, PEMT, and glycerolipid biosynthetic pathways. CONCLUSIONS: Our work unveils differential infrastructure of the lipid networks in visceral and subcutaneous adipose tissues and suggests an integrative pathway, with a discriminative flux between adipose tissues.

The FCS-like zinc finger scaffold of the kinase SnRK1 is formed by the coordinated actions of the FLZ domain and intrinsically disordered regions.

The SNF1-related protein kinase 1 (SnRK1) is a heterotrimeric eukaryotic kinase that interacts with diverse proteins and regulates their activity in response to starvation and stress signals. Recently, the FCS-like zinc finger (FLZ) proteins were identified as a potential scaffold for SnRK1 in plants. However, the evolutionary and mechanistic aspect of this complex formation is currently unknown. Here, in silico analyses predicted that FLZ proteins possess conserved intrinsically disordered regions (IDRs) with a propensity for protein binding in the N and C termini across the plant lineage. We observed that the Arabidopsis FLZ proteins promiscuously interact with SnRK1 subunits, which formed different isoenzyme complexes. The FLZ domain was essential for mediating the interaction with SnRK1α subunits, whereas the IDRs in the N termini facilitated interactions with the ß and ßγ subunits of SnRK1. Furthermore, the IDRs in the N termini were important for mediating dimerization of different FLZ proteins. Of note, the interaction of FLZ with SnRK1 was confined to cytoplasmic foci, which colocalized with the endoplasmic reticulum. An evolutionary analysis revealed that in general, the IDR-rich regions are under more relaxed selection than the FLZ domain. In summary, the findings in our study reveal the structural details, origin, and evolution of a land plant-specific scaffold of SnRK1 formed by the coordinated actions of IDRs and structured regions in the FLZ proteins. We propose that the FLZ protein complex might be involved in providing flexibility, thus enhancing the binding repertoire of the SnRK1 hub in land plants.

Comprehensive Evolutionary and Expression Analysis of FCS-Like Zinc finger Gene Family Yields Insights into Their Origin, Expansion and Divergence.

Plant evolution is characterized by frequent genome duplication events. Expansion of habitat resulted in the origin of many novel genes and genome duplication events which in turn resulted in the expansion of many regulatory gene families. The plant-specific FCS-Like Zinc finger (FLZ) gene family is characterized by the presence of a FCS-Like Zinc finger (FLZ) domain which mediates the protein-protein interaction. In this study, we identified that the expansion of FLZ gene family size in different species is correlated with ancestral and lineage-specific whole genome duplication events. The subsequent gene loss found to have a greater role in determining the size of this gene family in many species. However, genomic block duplications played the significant role in the expansion of FLZ gene family in some species. Comparison of Arabidopsis thaliana and Oryza sativa FLZ gene family revealed monocot and dicot specific evolutionary trends. The FLZ genes were found to be under high purifying selection. The spatiotemporal expression analyses of Arabidopsis thaliana FLZ gene family revealed that majority of the members are highly expressed in reproductive organs. FLZ genes were also found to be highly expressed during vegetative-to-reproductive phase transition which is correlated with the proposed role of this gene family in sugar signaling. The comparison of sequence, structural and expression features of duplicated genes identified lineage-specific redundancy and divergence. This extensive evolutionary analysis and expression analysis of Arabidopsis thaliana FLZ genes will pave the way for further functional analysis of FLZ genes.