TITLE:
Validation of Reference Genes for mRNA Quantification in Adjuvant Arthritis
AUTHORS:
Muhammad Ayaz Alam Qureshi, Aisha Siddiqah Ahmed, Jian Li, André Stark, Per Eriksson, Mahmood Ahmed
KEYWORDS:
Quantitative PCR; Adjuvant Arthritis; Housekeeping Gene
JOURNAL NAME:
Open Journal of Rheumatology and Autoimmune Diseases,
Vol.2 No.3,
August
21,
2012
ABSTRACT: Real time quantitative PCR (RT-qPCR) requires a method to normalize the expression of target genes against an en- dogenous reference gene. It is known that commonly used housekeeping genes (HKGs) vary tremendously in inflam- matory conditions; however information about the stability and expression of HKGs in chronic inflammatory joint dis- ease such as rheumatoid arthritis (RA) is scarce. The expressional stability of 10 commonly used HKGs was analyzed in the neuronal (spinal cord, dorsal root ganglia) and in the musculoskeletal tissues (tendon, muscle, epiphysis, capsule, periosteum and ankle joint) using RT-qPCR in the rat model of RA. In individual tissues, suitable HKGs were selected by | △Ct| (│Ct control-Ct arthritis│) and further analyzed by using software programs; geNorm and normfinder. We found hypoxanthine-guanine phosphoribosyl tranferase (HPRT) as the most stable gene except ankle joint while glyce-raldehyde-3-phosphate dehydrogenase (GAPDH) was found as the least stable gene in musculoskeletal tissues. In in-flamed ankle joint where no reference gene was found to be stably expressed, an inflammatory cell marker CD3 was used to normalize peptidylprolyl isomerase B (PPIB), the most homogenous HKG identified among the 10 HKGs. The normalized PPIB was then used to analyze the gene expression of neurokinin 1 (NK1), receptor of substance P, a potent pro-inflammatory mediator. We observed a 3.5 fold increase (p = 0.009) in NK1 expression in inflamed ankle joint compared to control. Our results indicate that reference genes stability should be evaluated before using them as refer- ence during inflammatory conditions. In tissues with intense inflammatory cell infiltration, an inflammatory cell marker should be used to normalize the selected reference gene to avoid erroneous results.