Sites of amyloid SAA mRNA production

To investigate possible extrahepatic sites of SAA production, male BALB/c mice were given a single 0.5 ml injection of either 10% casein or lipopolysaccharide (LPS; 100 mg/ml). Twenty hours after injection, RNA was extracted from liver, kidney, adrenal, testis, brain, spleen, skeletal muscle, heart, lung and small intestine. Northern blots of total RNA were hybridized with nick-translated /sup 32/P-labeled cDNA probes (length approximately 150 base pairs) corresponding to an homologous region of the three known SAA genes. Both casein and LPS elevated the mRNA in liver to about 200-fold above control levels; mRNA was elevated in adrenals from O to approximately 2% of liver. mRNA in some other tissues responded only to LPS injection: levels in kidney reached 15% of liver; pituitary, testis and brain reached 0.02 to 0.5% of liver; no apoSAA mRNA was detected in heart, skeletal muscle, lung, spleen or small intestine. Thus, some organs other than liver appear to have operational genes for apoSAA. The expression of apoSAA genes in different tissues is shared with other apoproteins; it remains to be seen whether all three or only selected genes are transcribed and translated in different tissues.