Influence of Age on Cerebral Housekeeping Gene Expression for Normalization of Quantitative Polymerase Chain Reaction after Acute Brain Injury in Mice.

To prevent methodological errors of quantitative PCR (qPCR) normalization with reference genes is obligatory. Although known to influence gene expression, impact of age on housekeeping gene expression has not been determined after acute brain lesions such as traumatic brain injury (TBI). Therefore, expression of eight common control genes was investigated at 15 min, 24 h, and 72 h after experimental TBI in 2- and 21-month-old C57Bl6 mice. Expression of β2-microglobulin (B2M), β-actin (ActB), and porphobilinogen deaminase (PBGD) increased after TBI in both ages. β2M demonstrated age-dependent differences and highest inter- and intragroup variations. Expression of cyclophilin A, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), hypoxanthine ribosyltransferase (HPRT), S100B, and 18SrRNA remained stable. Cyclophilin A and HPRT demonstrated strongest inter- and intragroup stability. The data indicate that the expression of most but not all control genes is stable during aging. The correct choice of housekeeping genes is of key importance to ensure adequate normalization of qPCR data. With respect to insult and age, normalization strategies should consider cyclophilin A as a single normalizer. Normalization with two reference genes is recommended with cyclophilin A and HPRT in young mice and in mixed age studies and with cyclophilin A and GAPDH in old mice. In addition, the present study suggests not to use β2-microglobulin, β-actin or PBGD as single control genes because of strong regulation after CCI in 2- and 21-month-old mice.