I would like to compare PPARγ expression among healthy person based on their nutrition, but I cannot find the normal range for PPARγ. I also does not have a negative control or positive control for PPARγ gene. How should I do? Anyone has suggestion?
The normal differentiated adipocytes in any tissues express PPAR-gamma, so that you can use as control. On the other hand, muscle cells or epithelial cells in the skin do not totally express this nuclear transcriptional receptor.
I do not think there is an established standard what constitutes "normal" PPARgamma expression in humans. PPARgamma levels have been shown to be influenced by genetic components (SNPs) at the level of transcription. Moreover, the PPARgamma levels may vary between different depots of fat, and there is no way to be sure that adipose biopsies from different patients are functionally equivalent, unless you performed an extensive analysis of cell-type specific markers. Diet is yet another variable that may influence PPARg levels. Taken together, it is fair to expect to see a wide range of PPARg levels across individuals.
In the end, you will need to approach this statistically- try to sample a large number of "normal diet" individuals and see the range of expression. Once you have some empirical measurements, you can figure out how best to design your study to tease out a potential influence of diet on PPARg expression with some statistical certainty.
In terms of control samples, I would suggest transfecting 293T cells with a PPARg expression plasmid. This will yield tons of material for a positive control. Use non-transfected cells as your negative control.
There are different isoforms of PPARg expressed in different tissues. Many naturally occurring molecules can influence their expression. For a review, please look here:
https://www.researchgate.net/publication/264429876_Natural_product_agonists_of_peroxisome_proliferator-activated_receptor_gamma_%28PPAR%29_a_review
Article Natural product agonists of peroxisome proliferator-activate...
To get the "normal" range (the most common Cq) of PPARg in different tissues of healthy persons, I would strongly recommend the swiss-based bioinformatics tool Genevestigator. It integrates many published microarray data. In its free edition, you could rapidly identify a good positive/negative control for PPPARg, and also you could identify a gene to be used as a reference gene.
Then, check out the samples available for any given tissue and choose the ones that seem "normal", eg. that come from a person without any metabolic disturbance. Although the expression scale is taken from microarray data, I found that what is classified as "low" has a Cq bigger than 30, "average" corresponds to Cq 20-30 and "high" - below 20.
In its paid version Genevestigator offers much much more. Upon registration, full access is given for 7 days - try it out!
https://www.genevestigator.com/gv/
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