An RNA-immunoprecipitation via CRISPR/dCas13 reveals an interaction between the SARS-CoV-2 5'UTR RNA and the process of human lipid metabolism.

We herein elucidate the function of SARS-CoV-2derived 5'UTR in the human cells. 5'UTR bound host cellular RNAs were immunoprecipitated by gRNA-dCas13 (targeting luciferase RNA fused to SARS-CoV-2 5'UTR) in HEK293T and A549 cells. The 5'UTR bound RNA extractions were predominantly enriched for regulating lipid metabolism. Overexpression of SARS-CoV-2 5'UTR RNA altered the expression of factors involved in the process of the human Mevalonate pathway. In addition, we found that HMG-CoA reductase inhibitors were shown to suppress SARS-CoV-2 5'UTR-mediated translation activities. In conclusion, we deduce the array of host RNAs interacting with SARS-CoV-2 5'UTR that drives SARS-CoV-2 translation and influences host metabolic pathways.

Structure-based design of gRNA for Cas13.

Cas13 endonuclease activity depends on the RNA local secondary structure with strong preference for single-stranded (SS) regions. Hence, it becomes indispensable to identify the SS regions for effective Cas13 mediated RNA knockdown. We herein present rational gRNA design by integrating experimental structure-seq data and predicted structural models. Utilizing structure-seq data for XIST transcript, we observed that gRNAs targeting the SS regions significantly induce transcript knockdown and cleavage than those targeting double-stranded (DS) regions. Further, we identified the "central seed region" in the gRNA that upon targeting the SS regions efficiently facilitates Cas13 mediated cleavage. In our following pursuits, we considered the scenario wherein experimental structure-seq data is not available, hence we used SS18-SSX2 fusion transcript indicated in synovial sarcomas and computationally predicted its structure. We observed that gRNAs targeting the SS regions predicted from the structure, efficiently induced necrosis compared to gRNAs that target the DS regions. In conclusion, for the effective RNA knockdown, the Cas13 mediated targeting strategy presented herein emphasizes the designing of gRNAs specifically targeting SS regions by utilizing structural information. Further, this strategy, in turn, can be anticipated to narrow the search space for gRNA design (by exclusively targeting SS regions) especially when lncRNAs are the targets.

Spred2 Regulates High Fat Diet-Induced Adipose Tissue Inflammation, and Metabolic Abnormalities in Mice.

Chronic low-grade inflammation in visceral adipose tissues triggers the development of obesity-related insulin resistance, leading to the metabolic syndrome, a serious health condition with higher risk of cardiovascular disease, diabetes, and stroke. In the present study, we investigated whether Sprouty-related EVH1-domain-containing protein 2 (Spred2), a negative regulator of the Ras/Raf/ERK/MAPK pathway, plays a role in the development of high fat diet (HFD)-induced obesity, adipose tissue inflammation, metabolic abnormalities, and insulin resistance. Spred2 knockout (KO) mice, fed with HFD, exhibited an augmented body weight gain, which was associated with enhanced adipocyte hypertrophy in mesenteric white adipose tissue (mWAT) and deteriorated dyslipidemia, compared with wild-type (WT) controls. The number of infiltrating macrophages with a M1 phenotype, and the crown-like structures, composed of macrophages surrounding dead or dying adipocytes, were more abundant in Spred2 KO-mWAT compared to in WT-mWAT. Exacerbated adipose tissue inflammation in Spred2 KO mice led to aggravated insulin resistance and fatty liver disease. To analyze the mechanism(s) that caused adipose tissue inflammation, cytokine response in mWAT was investigated. Stromal vascular fraction that contained macrophages from Spred2 KO-mWAT showed elevated levels of tumor necrosis factor α (TNFα) and monocyte chemoattractant protein-1 (MCP-1/CCL2) compared with those from WT-mWAT. Upon stimulation with palmitate acid (PA), bone marrow-derived macrophages (BMDMs) derived from Spred2 KO mice secreted higher levels of TNFα and MCP-1 than those from WT mice with enhanced ERK activation. U0126, a MEK inhibitor, reduced the PA-induced cytokine response. Taken together, these results suggested that Spred2, in macrophages, negatively regulates high fat diet-induced obesity, adipose tissue inflammation, metabolic abnormalities, and insulin resistance by inhibiting the ERK/MAPK pathway. Thus, Spred2 represents a potential therapeutic tool for the prevention of insulin resistance and resultant metabolic syndrome.