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This protocol presents the use of CRISPR SunTag-p65-HSF1 (SPH) in adipocytes (AdipoSPH) as an alternative strategy to adeno-associated virus (AAV) for investigating beige fat biology. In vivo injection of AAV-carrying sgRNA targeting the endogenous Prdm16 gene is sufficient to induce beige fat development and enhance the thermogenic gene program.
Clustered regularly interspaced short palindromic repeats (CRISPR) technology has prompted a revolution in biology, and recent tools have been applied far beyond the originally described gene editing. The CRISPR activation (CRISPRa) system combines the catalytically inactive Cas9 (dCas9) protein with distinct transcription modules to induce endogenous gene expression. SunTag-p65-HSF1 (SPH) is a recently developed CRISPRa technology that combines components of synergistic activation mediators (SAMs) with the SunTag activators. This system allows the overexpression of single or multiple genes by designing a customized single-guide RNA (sgRNA). In this study, a previously developed SPH mouse was used to generate a conditional mouse expressing SPH in adipocytes (adiponectin Cre lineage), named AdipoSPH. To induce a white-to-beige fat (browning) phenotype, an adeno-associated virus (AAV) carrying sgRNA targeting the endogenous Prdm16 gene (a well-established transcription factor related to brown and beige fat development) was injected into the inguinal white adipose tissue (iWAT). This mouse model induced the expression of endogenous Prdm16 and activated the thermogenic gene program. Moreover, in vitro SPH-induced Prdm16 overexpression enhanced the oxygen consumption of beige adipocytes, phenocopying the results of a previous Prdm16 transgenic mouse model. Thus, this protocol describes a versatile, cost-effective, and time-effective mouse model for investigating adipose tissue biology.
Beige (or brite) adipocytes are uncoupling protein 1 (UCP1)-expressing and mitochondrial-rich adipocytes that reside within white adipose tissue (WAT) depots. Beige fat emerges from a subset of adipocyte progenitors or mature white adipocytes in response to cold exposure and other stimuli1,2. Beige adipocytes can convert energy into heat in a UCP1-dependent or independent manner3. Regardless of its thermogenic function, beige fat can also improve metabolic health by other means, such as the secretion of adipokines and anti-inflammatory and anti-fibrotic activities. Studies in mice and humans have shown that the induction of beige fat improves whole-body glucose and lipid homeostasis3. However, although our knowledge of beige fat biology has evolved rapidly in recent years, most of its metabolic benefits and related mechanisms are still not fully understood.
Clustered regularly interspaced short palindromic repeats (CRISPR) were first described in eukaryotic cells as a tool capable of generating a double-strand break (DSB) at a specific site in the genome through the nuclease activity of the Cas9 protein4,5. Cas9 is guided by a synthetic single-guide RNA (sgRNA) to target a specific genomic region, leading to a DNA DSB. In addition to using the nuclease Cas9 for editing purposes, CRISPR-Cas9 technology has evolved to be used as a sequence-specific gene regulation tool6. The development of a catalytically inactive Cas9 protein (dCas9) and the association of transcriptional modules capable of enhancing gene expression has given rise to CRISPR activation (CRISPRa) tools. Several CRISPRa systems have emerged, such as VP647,8, synergistic activation mediator (SAM)9, SunTag10,11, VPR12,13, and SunTag-p65-HSF1 (SPH)14, which combines the components of SAM and SunTag activators. It has recently been demonstrated that the induced expression of neurogenic genes in N2a neuroblasts and primary astrocytes is higher using SPH compared to other CRISPRa systems14, demonstrating SPH as a promising CRISPRa tool.
Here, we took advantage of a previously developed SPH mouse14 to generate a conditional mouse model expressing SPH specifically in adipocytes using the adiponectin Cre lineage (AdipoSPH). Using an adeno-associated virus (AAV) carrying the gRNA targeting the endogenous Prdm16 gene, browning (white to beige conversion) of inguinal WAT (iWAT) was induced to increase the expression of the thermogenic gene program. Moreover, in vitro Prdm16 overexpression enhanced oxygen consumption. Therefore, this protocol provides a versatile SPH mouse model for exploring the mechanisms of beige fat development within adipose tissue.
Animal studies were performed in accordance with the University of Campinas Guide for the Care and Use of Laboratory Animals (protocol CEUA #5810-1/2021).
1. Molecular cloning
2. AAV packaging
NOTE: AAV packaging was performed according to previous publications15,16 with minor modifications.
3. Titration of the AAV by qPCR
4. In vivo injection of AAV into the inguinal white adipose tissue (iWAT)
5. In vitro differentiation of stromal vascular cells (SVFs) into beige adipocytes
6. In vitro AAV infection of SVFs
NOTE: SVFs derived from AdipoSPH mice iWAT were infected with AAV-carrying sgRNA-Prdm16 as previously described by Wang et al.18 with a few modifications.
AdipoSPH mice were developed by breeding SPH and Adipoq-Cre mouse strains. Both mouse strains were in a hybrid C57BL6J-DBA/2J background (according to the commercial supplier; see Table of Materials). The SPH mouse lineage was originally described by Zhou et al.14.
In vivo beige adipocyte development through AdipoSPH-mediated Prdm16 overexpression
To evaluate the capacity of the model described in this st...
One of the most useful non-editing applications of CRISPR technology is the interrogation of gene function through the activation of endogenous genes using CRISPRa systems6. SPH is a powerful CRISPRa that was originally described to induce the conversion of astrocytes into active neurons by targeting several neurogenic genes14. In this study, AdipoSPH was demonstrated to be a suitable tool for investigating beige fat biology by activating the expression of endogenous Prdm16...
The authors have nothing to disclose.
The authors thank the support received from Centro Multidisciplinar para Investigação Biológica na Área da Ciência em Animais de Laboratório (Cemib), Unicamp, for the generation of AdipoSPH mice, the Inmmunometabolism and Cell Signaling Laboratory, and National Institute of Science and Technology on Photonics Applied to Cell Biology (INFABIC) for all experimental support. We thank the financial support from Sao Paulo Research Foundation (FAPESP): 2019/15025-5; 2020/09308-1; 2020/14725-0; 2021/11841-2.
Name | Company | Catalog Number | Comments |
3,3',5-Triiodo-L-thyronine | Sigma-Aldrich | T2877 | |
3-Isobutyl-1-methylxanthine | Sigma-Aldrich | I5879 | |
AAVpro 293T Cell Line | Takarabio | 632273 | |
Amicon Ultra Centrifugal Filter | Merckmillipore | UFC510008 | 100 KDa |
Dexamethasone | Sigma-Aldrich | D1756 | |
Dulbecco's Modification of Eagles Medium (DMEM) | Corning | 10-017-CV | |
Dulbecco's Modified Eagle Medium (DMEM) F-12, GlutaMAX™ supplement | Gibco | 10565-018 | high concentrations of glucose, amino acids, and vitamins |
Dulbecco's phosphate buffered saline (DPBS) | Sigma-Aldrich | D8662 | |
Excelta Self-Opening Micro Scissors | Fisher Scientific | 17-467-496 | |
Fetal bovine serum | Sigma-Aldrich | F2442 | |
Fisherbrand Cell Scrapers (100 pk) | Fisher Scientific | 08-100-241 | |
Fisherbrand High Precision Straight Tapered Ultra Fine Point Tweezers/Forceps | Fisher Scientific | 12-000-122 | |
Fisherbrand Sharp-Pointed Dissecting Scissors | Fisher Scientific | 08-940 | |
Glycerol | Sigma-Aldrich | G5516 | |
HEPES | Sigma-Aldrich | H3375-25G | |
Hexadimethrine bromide (Polybrene) | Sigma-Aldrich | H9268 | |
Indomethacin | Sigma-Aldrich | I7378 | |
Insulin | Sigma-Aldrich | I9278 | |
LigaFast Rapid DNA Ligation System | Promega | M8225 | |
Maxiprep purification kit | Qiagen | 12162 | |
Microliter syringe | Hamilton | 80308 | Model 701 |
NEB 10-beta/Stable | New England Biolabs | C3019H | E. coli competent cells |
pAAV2/8 | Addgene | 112864 | |
pAAV-U6-gRNA-CBh-mCherry | Addgene | 91947 | |
pAdDeltaF6 | Addgene | 112867 | |
PEG 8000 | Sigma-Aldrich | 89510 | |
Penicillin/streptomycin | Gibco | 15140-122 | |
Polyethylenimine | Sigma-Aldrich | 23966 | Linear, MW 25000 |
Povidone-iodine | Rioquímica | 510101303 | Antiseptic |
Rosiglitazone | Sigma-Aldrich | R2408 | |
SacI enzyme | New England Biolabs | R0156 | |
Surgical Design Premier Adson Forceps | Fisher Scientific | 22-079-741 | |
Syringe | Hamilton | 475-40417 | |
T4 DNA Ligase | Promega | M180B | |
T4 DNA ligase buffer | New England Biolabs | B0202S | |
T4 PNK enzyme kit | New England Biolabs | M0201S | |
Tramadol Hydrochloride | SEM | 43930 | |
Vidisic Gel | Bausch + Lomb | 99620 |
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