Preparation of rAAV9 to Overexpress or Knockdown Genes in Mouse Hearts

The overall goal of this procedure is to prepare recombinant adeno-associated virus nine, or rAAV9, to manipulate gene expression in mouse hearts. The method can answer key question in the field of cardiology and molecular genetics, such as how to study gene function in mouse heart in vivo. The main advantage of this technique is that it will allow us to easily manipulate the gene expression and function in vivo in mouse heart, allowing the functional access of gene function without having to rely on the genetically modified animal models.

After generating rAAV9 constructs and culturing HEK293 cells according to the text protocol, to transfect the cells on day one, combine 70 micrograms of AAV Rep-Cap plasmid, 70 micrograms of rAAV9 plasmid, and 200 micrograms of Ad helper plasmid in a 50-milliliter centrifuge tube. Add 49 milliliters of room temperature DMEM without FBS to the tube and mix well. Then, to make a four-to-one PEI to DNA solution, add 1, 360 microliters of PEI to the tube and mix well.

Incubate the solution at room temperature for 15 to 30 minutes. After the incubation, add five milliliters of the solution to each 150-milliliter dish of cells. Culture the cells at 37 degrees Celsius and 5%CO2 for 50 to 72 hours.

To harvest the transfected cells, dislodge and suspend the cells by using the culture medium to pipette up and down. Then transfer the cell suspensions to sterile 50-milliliter tubes. Centrifuge the cells at 500 times G for five minutes.

Then add five milliliters of PBS to each tube and re-suspend the cell pellets before combining all the suspensions in one 50-milliliter tube. After spinning the cells at 500 times G for five minutes, discard the supernatant. To purify the AAV, re-suspend the pellet in 10 milliliter of lysis buffer.

Freeze the lysate at minus 80 degrees Celsius or in a dry ice ethanol bath. Then thaw it at 37 degrees Celsius. Vortex the lysate for one minute before repeating the freeze and thaw two more times.

Next, add one millimolar magnesium chloride to the thawed lysate. Then add nuclease to a final concentration of 250 units per milliliter. Incubate the solution at 37 degrees Celsius for 15 minutes to dissolve the DNA protein aggregation.

Centrifuge the sample at 4, 800 times G and four degrees Celsius for 20 minutes. Then collect the supernatant. Meanwhile, to prepare a 17%iodixanol gradient solution, mix five milliliters of 10X PBS with 0.05 milliliters of one molar magnesium chloride, 0.125 milliliters of one molar potassium chloride, 10 milliliters of five molar sodium chloride, and 12.5 milliliters of density gradient medium.

Use water to adjust the total volume to 50 milliliters. After preparing 25, 40, and 60%gradient solutions according to the text protocol, use a needle and syringe to load five milliliters of 17%gradient solution into a polypropylene tube. Follow this with five milliliters each of 25, 40, and 60%gradient solutions.

Layer the lysate on top of the gradient. Then fill the tube with lysis buffer and cover it with a cork. Centrifuge the gradient at 185, 000 times G and 16%Celsius for 90 minutes.

Following the spin, use a syringe to harvest the 40%viral fraction by inserting a 21 gauge needle into the intersection between the 40 and 60%fractions, completely avoiding the 25%layer. Mix the viral fraction with sterilized polyoxyethylene polyoxypropylene, or PEG-PPG block copolymer PBS solution, up to a total volume of 15 milliliters. Load the mixture into a filter tube with a molecular weight cutoff of 100 kilodaltons.

Then centrifuge the sample at 2, 000 times G and four degrees Celsius for 30 minutes. Decant the solution from the bottom of the tube. Then use PEG-PPG to refill the filter tube to 15 milliliters.

Centrifuge the tube at 2, 000 times G and four degrees Celsius for 20 minutes. After repeating the refilling and spin two more times, collect the purified rAAV9 virus fraction still above the filter. Aliquot 100 to 400 microliters of the purified rAAV9 into 1.7-milliliter tubes, depending on the viral titer, and store the virus at minus 80 degrees Celsius.

After determining the viral titer according to the text protocol, prepare rAAV9 working solutions with virus titers of one to seven times 10 to the 12th particles per milliliter. To treat neonatal mice, use the rAAV9 solution to pre-fill a 0.33 by 12.7-milliliter insulin syringe with a 29 gauge one-half inch needle, avoiding air bubbles. After cryo-anesthetizing a pup, hold the pup in one hand with thumb and forefinger, then swipe the back skin of the pup with a swab stick saturated with 70%isopropyl alcohol.

Insert the syringe into the anterior dorsal subcutis of the animal at an angle of five to 10 degrees before injecting 50 to 70 microliters of the rAAV9 solution. The standard curve for rAAV9 titration was generated with the qPCR data by linear regression. The manipulated variable y represents the log10 value of the DNA molecular concentration of each standard sample, and the corresponding variable x represents the Ct value.

The log10 concentration values and Ct numbers exhibit a nice linear correlation and fit with the equation shown here. Titers of rAAV9 samples were calculated based on the linear equation. Using the method demonstrated in this video, a high titer of rAAV9 vectors was obtained in this representative study.

To monitor the efficiency and tissue specificity of rAAV9 cTNT vectors, P0.5 pups were treated with the same amount of rAAV9 cTNT luciferase or rAAV9 cTNT GFP by subcutaneous injection. Two weeks after injection, robust expression of GFP was detected in the heart but not in other organs. To monitor the knockdown efficiency and tissue specificity of rAAV9 U6 vectors, P0.5 mice were treated with the same amount of rAAV9 U6 scramble or rAAV9 U6 Trbp shRNA by subcutaneous injection.

Two weeks after injection, the mRNA level of Trbp in the heart was substantially reduced by rAAV9 U6 shTrbp. Down-regulation of Trbp was also detected to a lesser extent in the liver. Once mastered, rAAV preparation can be done in five days, if it is formulated properly.

While attempting this procedure, it is important to remember to use healthy 293 cells for rAAV packaging. After its development, this technique paved the way for researchers in the field of cardiology and genetics to explore gene functions and gene therapeutic potentials in mouse hearts. After watching this video, you should have a good understanding of how to prepare recombinant AAV9 to manipulate the gene expressing any function in mouse hearts.