Aromatase cytochrome P450 transcripts are detected in fractured human bone but not in normal skeletal tissue

Peripheral conversion of gender steroid precursors has been implicated in playing a role in bone turnover in postmenopausal women. It has been reported that aromatase cytochrome P450 (P450arom) is present in primary bone and bone marrow (BM), and that P450arom mRNA has been identified in cultured BM and osteoblast-like cell lines. However, there are no reports that P450arom transcripts have been detected in skeletal tissue that has not been cultured. We therefore elected to test for the presence of P450arom mRNA in primary human bone and BM in normal and fractured necks of femora using the reverse transcription-polymerase chain reaction method. Although the RNA extracted from these tissues was of good quality as demonstrated by the expression of transcripts for interleukin-6, P450arom transcripts failed to be detected in normal primary cortical bone and fatty BM containing trabecular bone. However, P450arom transcripts were detected in the latter when they were cultured. Transcripts for P450arom were also detected in total RNA extracted from six fractured necks of femora and semiquantitative PCR demonstrated that P450arom mRNA was present in similar abundance in the same amount of RNA analyzed from buttock adipose tissue and fractured bone/BM. P450arom mRNA expression was also detected in cultured peripheral blood leukocytes, suggesting that this might be the source of the enzyme. In these cultures no correlation was detected between the expression of P450arom mRNA and cell proliferation. PCR failure was excluded in cases when P450arom transcripts failed to be detected in bone/BM by coamplifying RNA from human and rat brain mRNA, known to express P450arom mRNA, using primers that detect both P450arom mRNA from both species. These products were analyzed by Southern blot using oligonucleotide probes, which label either human or rat P450arom cDNA. The blots confirmed the absence of P450arom in nonfractured human bone and BM and preclude PCR failure. Our results indicate that P450arom mRNA is not detected in either normal human bone or BM, but can be induced in this microenvironment under pathological conditions. We propose that tissue grown in vitro is analogous to a wound and this explains why P450arom transcripts were detected in cultured normal skeletal tissue, whereas they failed to be detected in primary normal bone and BM.