Housekeepers for accurate transcript expression analysis in Alzheimer's disease autopsy brain tissue

BACKGROUND

Quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) is a popular technique for mRNA expression studies. Normalization to an endogenous reference transcript (housekeeper) is widely used to correct for differences in loading and RNA quality. Alzheimer's disease (AD) alters brain metabolism. The stability of housekeeper transcript expression must be carefully validated.

METHODS

qRT-PCR was used to assess eight putative housekeeper transcripts in four brain regions from 15 control, 12 AD, and 10 AD/Lewy body disease (LBD) cases.

RESULTS

RNA quality is lower in AD and AD/LBD than in controls. Frequently used housekeepers such as glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and β-actin had lower overall expression in AD and AD/LBD cases than in controls. RPL13 and 18S were the most stably expressed housekeepers tested. Synaptophysin and glial fibrillary acidic protein were used to evaluate normalized quantification. By using different housekeepers we confirmed that synaptophysin expression was down-regulated in AD cases, whereas glial fibrillary acidic protein expression was increased.

CONCLUSIONS

Among all candidates tested, RPL13 was the best housekeeper for qRT-PCR studies in autopsy brain tissue samples from controls and AD cases. RNA quality should be assessed and data normalized on this index as well.

Radioimmunoassay for rat B-type natriuretic peptide (BNP-45)

Rat BNP-45 is the main circulating form of BNP in rat plasma. To understand the role of BNP in physiological and pathophysiological conditions, a specific radioimmunoassay (RIA) for the quantitative determination of the peptide in plasma and tissues is necessary. An assay using rBNP-45 as the standard in conjunction with antisera directed against this peptide has not been described in the literature, though some investigators have reported values ranging from 0.73-2.0 pmol/L using either BNP-26 or BNP-32 as the standard peptide. Unfortunately, these forms of BNP do not exist in rat plasma. In our studies, we have developed a specific RIA for rBNP-45 using rBNP-45 as the standard peptide and Tyro-rBNP-45 as the radioligand. We have used two specific antisera for assay purposes; one against rBNP-45, and the second to a peptide composed of the first 20 amino acids of rBNP-45 (rBNP[1-20]). The recovery of various amounts of rBNP-45 added to control plasma was 50-80% depending on the method of extraction and purification. The interassay and intraassay coefficients of variation were 12% and 6% respectively. Values obtained were similar for blood sampled by either cardiac puncture, decapitation, or aortic puncture. The method was used to measure rBNP-45 in the plasma of normal (WKY) and Spontaneously Hypertensive (SHR) rats. The values obtained were 5.46 +/- 0.43 and 19.6 +/- 2.36 pmol/L respectively. The rat atrial natriuretic peptide (ANP[99-126]) values in the same extracts were 23.2 +/- 0.45 and 51.6 +/- 3.16 pmol/L.