Concept of lipid droplet biogenesis

Phosphatidic acid drives spatiotemporal distribution of Pex30 at ER-LD contact sites

Lipid droplets (LDs) are ubiquitous neutral lipid storage organelles that form at discrete subdomains in the ER bilayer. The assembly of these ER subdomains and the mechanism by which proteins are recruited to them is poorly understood. Here, we investigate the spatiotemporal distribution of Pex30 at the ER-LD membrane contact sites (MCSs). Pex30, an ER membrane-shaping protein, has a reticulon homology domain, a dysferlin (DysF) domain, and a Duf4196 domain. Deletion of SEI1, which codes for seipin, a highly conserved protein required for LD biogenesis, results in accumulation of Pex30 and phosphatidic acid (PA) at ER-LD contact sites. We show that PA recruits Pex30 at ER subdomains by binding to the DysF domain. The distribution of Pex30 as well as PA is also affected by phosphatidylcholine (PC) levels. We propose that PA regulates the spatiotemporal distribution of Pex30 at ER subdomains that plays a critical role in driving the formation of LDs in the ER membrane.

Porcine SCD1 Regulates Lipid Droplet Number via CLSTN3B in PK15 Cells

Fat deposition plays a key role in determining porcine meat quality traits, with lipid droplets serving as critical organelles for lipid storage in adipose tissue. Inhibiting lipid droplet biogenesis disrupts the lipid storage capacity of adipocytes. The Stearoyl-CoA Desaturase (SCD) family is crucial in regulating polyunsaturated fatty acid/monounsaturated fatty acid (PUFA/MUFA) composition, while its role in lipid droplet formation remains unclear. This study employed CRISPR/Cas9 to create SCD1-deficient porcine renal epithelial cells (PK15), enabling an investigation into SCD1's role in fatty acid composition and lipid droplet regulation. RNA-seq analysis was conducted to elucidate the mechanisms underlying SCD1's impact on lipid droplet numbers. Results showed that SCD1 deletion significantly decreased triacylglycerols (TAG) content, altered fatty acid composition, and decreased lipid droplet numbers. Conversely, SCD1 overexpression increased lipid droplet numbers, confirming SCD1's role in regulating lipid droplet abundance. RNA-seq analysis revealed that SCD1 regulates lipid metabolism via Calsyntenin 3β (CLSTN3B). Experimental validation confirmed the SCD1-CLSTN3B regulation of lipid droplet numbers. In summary, we discovered the role of SCD1 in regulating the number of lipid droplets, highlighting its potential impact on lipid metabolism and adipocyte function in pigs.

Protocol to determine the topology of integral endoplasmic reticulum membrane protein in Saccharomyces cerevisiae

Here, we present a protocol to determine the topology of Fld1 (few lipid droplets), an integral endoplasmic reticulum (ER) membrane protein in Saccharomyces cerevisiae. We describe steps to generate functional N-terminal GFP and C-terminal mCherry fusion with Fld1. We detail the strategy to perform subcellular fractionation to isolate ER-derived microsomes that were subjected to salt detergent extraction analysis. We then provide procedures to determine the topology of Fld1 using proteinase K treatment.

Role of gliflozins on hepatocellular carcinoma progression: a systematic synthesis of preclinical and clinical evidence

INTRODUCTION

The risk of HCC is twice as high in diabetic patients compared to non-diabetic ones, suggesting that diabetes advances carcinogenesis in the liver through a variety of mechanisms. Sodium-glucose cotransporter 2 inhibitors (SGLT2i) have been shown to improve liver outcomes, emerging as promising agents to treat hepatocellular carcinoma (HCC) in patients with type 2 diabetes mellitus (T2DM).

METHODS

We searched PubMed and Scopus databases for articles presenting an association between SGLT2is and HCC to explore the putative mechanisms of action underlying the anti-proliferative activity of SGLT2is.

RESULTS

A total of 24 articles were selected for inclusion, of which 14 were preclinical and 10 were clinical. Preclinical studies were mainly focused on canagliflozin, used alone or in combination with other drugs.

CONCLUSIONS

Overall, canagliflozin had a negative effect on HCC cell proliferation by interfering with glucose-dependent and independent metabolic pathways, negatively impacting angiogenesis, and inducing apoptosis in in-vitro cell models. In-vivo, a protective effect on hepatic steatosis and fibrosis and HCC development has been reported. Human studies showed a lower risk of developing HCC in patients on SGLT2is. However, this is supported by retrospective cohort studies. Clinical trials are needed to confirm the causal relationship between SGLT2i administration and HCC development.

Identification and Characterization of Lipid Droplet-Associated Protein (LDAP) Isoforms from Tung Tree (Vernicia fordii)

Lipid droplets (LDs) are cytoplasmic organelles responsible primarily for the storage of neutral lipids, such as triacyclglycerols (TAGs). Derived from the endoplasmic reticulum bilayer, LDs are composed of a hydrophobic lipid core encased by a phospholipid monolayer and surface-associated proteins. To date, only a relatively few LD 'coat' proteins in plants have been identified and characterized, most of which come from studies of the model plant Arabidopsis thaliana. To expand our knowledge of the plant LD proteome, the LD-associated protein (LDAP) family from the tung tree (Vernicia fordii), whose seeds are rich in a commercially valuable TAG containing the conjugated fatty acid α-eleostearic acid (C18:3Δ9cis,11trans,13trans [α-ESA]), was identified and characterized. Based on the tung tree transcriptome, three LDAP isoforms (VfLDAP1-3) were elucidated and the encoded proteins distinctly clustered into three clades along with their respective isoforms from other angiosperm species. Ectopic expression of the VfLDAPs in Nicotiana benthamiana leaves revealed that they localized specifically to LDs and influenced LD numbers and sizes, as well as increasing TAG content and altering TAG fatty acid composition. Interestingly, in a partially reconstructed TAG-ESA biosynthetic pathway, the co-expression of VfLDAP3 and, to a lesser degree, VfLDAP2, significantly increased the content of α-ESA stored within the LDs. These results suggest that the VfLDAPs can influence the steady-state content and composition of TAG in plant cells and that certain LDAP isoforms may have evolved to more efficiently package TAGs into LDs containing unusual fatty acids, such as α-ESA.

The evolving landscape of ER-LD contact sites

Lipid droplets (LDs) are evolutionarily conserved dynamic organelles that play an important role in cellular physiology. Growing evidence suggests that LD biogenesis occurs at discrete endoplasmic reticulum (ER) subdomains demarcated by the lipodystrophy protein, Seipin, lack of which impairs adipogenesis. However, the mechanisms of how these domains are selected is not completely known. These ER sites undergo ordered assembly of proteins and lipids to initiate LD biogenesis and facilitate establishment of ER-LD contact sites, a prerequisite for proper growth and maturation of droplets. LDs retain both physical and functional association with the ER throughout their lifecycle to facilitate bi-directional communication, such as exchange of proteins and lipids between the two organelles at these ER-LD contact sites. In recent years several molecular tethers have been identified that bridge ER and LDs together including few proteins that are found exclusively at these ER-LD contact interface. Here, we discuss recent advances in understanding the role of factors that ensure functionality of ER-LD contact site machinery for LD homeostasis.

Lipid droplets in steatotic liver disease

PURPOSE OF REVIEW

This review aims to discuss the most recent evidence exploring the role of lipid droplets in steatotic liver disease (SLD). We highlight the breadth of mechanisms by which lipid droplets may contribute to the progression of SLD with a particular focus on the role of lipid droplets as inducers of mechanical stress within hepatocytes and genetic mutations in lipid droplet associated proteins. Finally, this review provides an update on clinical trials exploring the therapeutic potential and strategies targeting lipid droplets.

RECENT FINDINGS

The size, composition and location of hepatic lipid droplets strongly influence the pathological role of these organelles in SLD. Emerging studies are beginning to elucidate the importance of lipid droplet induced hepatocyte mechanical stress. Novel strategies targeting lipid droplets, including the effects of lipid droplet associated protein mutations, show promising therapeutic potential.

SUMMARY

Much more than a histological feature, lipid droplets are complex heterogenous organelles crucial to cellular metabolism with important causative roles in the development and progression of SLD. Lipid droplet induced mechanical stress may exacerbate hepatic inflammation and fibrogenesis and potentially contribute to the development of a pro-carcinogenic hepatic environment. The integration of advancements in genetics and molecular biology in upcoming treatments aspires to transcend symptomatic alleviation and address the fundamental causes and pathological development of SLD.