RXRα Positively Regulates Expression of the Chicken PLIN1 Gene in a PPARγ-Independent Manner and Promotes Adipogenesis

Perilipin1 (PLIN1), the most abundant lipid droplet (LD)-associated protein, plays a vital role in regulating lipid storage and breakdown in adipocytes. Recently, we found that the overexpression of PLIN1 promotes chicken preadipocyte lipid accumulation. However, the mechanisms by which transcription of the chicken PLIN1 gene is regulated remain unknown. In this study, we investigated the role of retinoid X receptor α (RXRα) in transcription of the chicken PLIN1 gene. Notably, reporter gene and expression assays showed that RXRα activates transcription of the chicken PLIN1 gene in a PPARγ-independent manner. Furthermore, promoter deletion and electrophoretic mobility shift assay (EMSA) analysis revealed that the chicken PLIN1 gene promoter region (-774/-785) contains an RXRα-binding site. Further study demonstrated that RXRα overexpression promotes differentiation of an immortalized chicken preadipocyte cell line (ICP1), causing a concomitant increase in PLIN1 transcripts. Taken together, our results show for the first time that RXRα activates transcription of the chicken PLIN1 gene in a PPARγ-independent manner, which might be at least in part responsible for RXRα-induced adipogenesis.

An overview of lipodystrophy and the role of the complement system

The complement system is a major component of innate immunity playing essential roles in the destruction of pathogens, the clearance of apoptotic cells and immune complexes, the enhancement of phagocytosis, inflammation, and the modulation of adaptive immune responses. During the last decades, numerous studies have shown that the complement system has key functions in the biology of certain tissues. For example, complement contributes to normal brain and embryonic development and to the homeostasis of lipid metabolism. However, the complement system is subjected to the effective balance between activation-inactivation to maintain complement homeostasis and to prevent self-injury to cells or tissues. When this control is disrupted, serious pathologies eventually develop, such as C3 glomerulopathy, autoimmune conditions and infections. Another heterogeneous group of ultra-rare diseases in which complement abnormalities have been described are the lipodystrophy syndromes. These diseases are characterized by the loss of adipose tissue throughout the entire body or partially. Complement over-activation has been reported in most of the patients with acquired partial lipodystrophy (also called Barraquer-Simons Syndrome) and in some cases of the generalized variety of the disease (Lawrence Syndrome). Even so, the mechanism through which the complement system induces adipose tissue abnormalities remains unclear. This review focuses on describing the link between the complement system and certain forms of lipodystrophy. In addition, we present an overview regarding the clinical presentation, differential diagnosis, classification, and management of patients with lipodystrophy associated with complement abnormalities.

Identification of gene products that control lipid droplet size in yeast using a high-throughput quantitative image analysis

Lipid droplets (LDs) are important organelles involved in energy storage and expenditure. LD dynamics has been investigated using genome-wide image screening methods in yeast and other model organisms. For most studies, genes were identified using two-dimensional images with LD enlargement as readout. Due to imaging limitation, reduction of LD size is seldom explored. Here, we aim to set up a screen that specifically utilizes reduced LD size as the readout. To achieve this, a novel yeast screen is set up to quantitatively and systematically identify genes that regulate LD size through a three-dimensional imaging-based approach. Cidea which promotes LD fusion and growth in mammalian cells was overexpressed in a yeast knockout library to induce large LD formation. Next, an automated, high-throughput image analysis method that monitors LD size was utilized. With this screen, we identified twelve genes that reduced LD size when deleted. The effects of eight of these genes on LD size were further validated in fld1 null strain background. In addition, six genes were previously identified as LD-regulating genes. To conclude, this methodology represents a promising strategy to screen for players in LD size control in both yeast and mammalian cells to aid in the investigation of LD-associated metabolic diseases.

A snake venom group IIA PLA2 with immunomodulatory activity induces formation of lipid droplets containing 15-d-PGJ2 in macrophages

Crotoxin B (CB) is a catalytically active group IIA sPLA₂ from Crotalus durissus terrificus snake venom. In contrast to most GIIA sPLA₂s, CB exhibits anti-inflammatory effects, including the ability to inhibit leukocyte functions. Lipid droplets (LDs) are lipid-rich organelles associated with inflammation and recognized as a site for the synthesis of inflammatory lipid mediators. Here, the ability of CB to induce formation of LDs and the mechanisms involved in this effect were investigated in isolated macrophages. The profile of CB-induced 15-d-PGJ₂ (15-Deoxy-Delta-12,14-prostaglandin J₂) production and involvement of LDs in 15-d-PGJ₂ biosynthesis were also investigated. Stimulation of murine macrophages with CB induced increased number of LDs and release of 15-d-PGJ₂. LDs induced by CB were associated to PLIN2 recruitment and expression and required activation of PKC, PI3K, MEK1/2, JNK, iPLA₂ and PLD. Both 15-d-PGJ₂ and COX-1 were found in CB-induced LDs indicating that LDs contribute to the inhibitory effects of CB by acting as platform for synthesis of 15-d-PGJ₂, a pro-resolving lipid mediator. Together, our data indicate that an immunomodulatory GIIA sPLA₂ can directly induce LD formation and production of a pro-resolving mediator in an inflammatory cell and afford new insights into the roles of LDs in resolution of inflammatory processes.

The metabolism of lymphomas

PURPOSE OF REVIEW

Cellular to animal to human studies are shedding light on metabolic pathways that contribute to sustaining lymphomagenesis. Old players with new metabolic tricks and new metabolic players come into the scene. The purpose of this review is to discuss the recent advances made in the field of lymphoma metabolism with special focus on the metabolic modulation of tumor promoting and suppressing pathways and, conversely, on the effect of these pathways on metabolite addiction.

RECENT FINDINGS

The basis for the high glucose uptake and glycolytic activity in lymphoma cells is now beginning to be understood. Recent findings suggest a greater role of nucleotide biosynthesis as a major driving force for glycolysis, especially during proliferation and cellular stress conditions. There is new evidence for an increasing contribution of glycine-folate metabolism deregulation in nucleotide biosynthesis, genome integrity and epigenetic maintenance. Expanding roles for MYC, PI3K and TP53 in regulating reactive oxygen production, glycolysis and glutaminolysis in lymphoma cells have been described. The identification of novel pathways has allowed the emergence of new 'antimetabolite' strategies to increase the therapeutic efficacy of current approaches.

SUMMARY

Metabolism in lymphomas must fulfill the general demands from cell proliferation and those specific to lymphomagenesis. Data emerging from preclinical studies are elucidating the metabolic pathways that contribute to maintaining the malignant phenotype in lymphomas. This has resulted in identification of novel pathways, some of which may have a clinical impact in the diagnosis, characterization and treatment of lymphoma subtypes.