Elevated Adipocyte Membrane Phospholipid Saturation Does Not Compromise Insulin Signaling.

Increased saturated fatty acid (SFA) levels in membrane phospholipids have been implicated in the development of metabolic disease. Here, we tested the hypothesis that increased SFA content in cell membranes negatively impacts adipocyte insulin signaling. Preadipocyte cell models with elevated SFA levels in phospholipids were generated by disrupting the ADIPOR2 locus, which resulted in a striking twofold increase in SFA-containing phosphatidylcholines and phosphatidylethanolamines, which persisted in differentiated adipocytes. Similar changes in phospholipid composition were observed in white adipose tissues isolated from the ADIPOR2-knockout mice. The SFA levels in phospholipids could be further increased by treating ADIPOR2-deficient cells with palmitic acid and resulted in reduced membrane fluidity and endoplasmic reticulum stress in mouse and human preadipocytes. Strikingly, increased SFA levels in differentiated adipocyte phospholipids had no effect on adipocyte gene expression or insulin signaling in vitro. Similarly, increased adipocyte phospholipid saturation did not impair white adipose tissue function in vivo, even in mice fed a high-saturated fat diet at thermoneutrality. We conclude that increasing SFA levels in adipocyte phospholipids is well tolerated and does not affect adipocyte insulin signaling in vitro and in vivo.

Intracellular Absolute Quantification of Oligonucleotide Therapeutics by NanoSIMS.

Antisense oligonucleotide (ASO)-based therapeutics hold great potential for the treatment of a variety of diseases. Therefore, a better understanding of cellular delivery, uptake, and trafficking mechanisms of ASOs is highly important for early-stage drug discovery. In particular, understanding the biodistribution and quantifying the abundance of ASOs at the subcellular level are needed to fully characterize their activity. Here, we used a combination of electron microscopy and NanoSIMS to assess the subcellular concentrations of a 34S-labeled GalNAc-ASO and a naked ASO in the organelles of primary human hepatocytes. We first cross-validated the method by including a 127I-labeled ASO, finding that the absolute concentration of the lysosomal ASO using two independent labeling strategies gave matching results, demonstrating the strength of our approach. This work also describes the preparation of external standards for absolute quantification by NanoSIMS. For both the 34S and 127I approaches used for our quantification methodology, we established the limit of detection (5 and 2 µM, respectively) and the lower limit of quantification (14 and 5 µM, respectively).

NanoSIMS Imaging Reveals the Impact of Ligand-ASO Conjugate Stability on ASO Subcellular Distribution.

The delivery of antisense oligonucleotides (ASOs) to specific cell types via targeted endocytosis is challenging due to the low cell surface expression of target receptors and inefficient escape of ASOs from the endosomal pathway. Conjugating ASOs to glucagon-like peptide 1 (GLP1) leads to efficient target knockdown, specifically in pancreatic ß-cells. It is presumed that ASOs dissociate from GLP1 intracellularly to enable an ASO interaction with its target RNA. It is unknown where or when this happens following GLP1-ASO binding to GLP1R and endocytosis. Here, we use correlative nanoscale secondary ion mass spectroscopy (NanoSIMS) and transmission electron microscopy to explore GLP1-ASO subcellular trafficking in GLP1R overexpressing HEK293 cells. We isotopically label both eGLP1 and ASO, which do not affect the eGLP1-ASO conjugate function. We found that the eGLP1 peptide and ASO are not detected at the same level in the same endosomes, within 30 min of GLP1R-HEK293 cell exposure to eGLP1-ASO. When we utilized different linker chemistry to stabilize the GLP1-ASO conjugate, we observed more ASO located with GLP1 compared to cell incubation with the less stable conjugate. Overall, our work suggests that the ASO separates from GLP1 relatively early in the endocytic pathway, and that linker chemistry might impact the GLP1-ASO function.

Building of neomycin-nucleobase-amino acid conjugates for the inhibition of oncogenic miRNAs biogenesis.

MicroRNAs (miRNAs) are a recently discovered category of small RNA molecules that regulate gene expression at the post-transcriptional level. Accumulating evidence indicates that miRNAs are aberrantly expressed in a variety of human cancers, thus being oncogenic. The inhibition of oncogenic miRNAs (defined as the blocking of miRNAs' production or function) would find application in the therapy of different types of cancer in which these miRNAs are implicated. In this work, we describe the design and synthesis of new small-molecule RNA ligands with the aim of inhibiting Dicer-mediated processing of oncogenic miRNAs. One of the synthesized compound (4b) composed of the aminoglycoside neomycin conjugated to an artificial nucleobase and to amino acid histidine is able to selectively decrease miR-372 levels in gastric adenocarcinoma (AGS) cells and to restore the expression of the target LATS2 protein. This activity led to the inhibition of proliferation of these cells. The study of the interactions of 4b with pre-miR-372 allowed for the elucidation of the molecular mechanism of the conjugate, thus leading to new perspectives for the design of future inhibitors.