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Rat alveolar macrophages express preprotachykinin gene-I mRNA-encoding tachykinins
C R Killingsworth1, S A Shore, F Alessandrini
1Physiology Program, Harvard School of Public Health, Boston, Massachusetts 02115, USA.
Abstract:
Although the tachykinins substance P (SP) and neurokinin A have been largely localized to neurons, eosinophils have also been shown to express these peptides. Our aim was to determine whether rat alveolar macrophages (AM) express preprotachykinin gene-I (PPT-I) mRNA that encodes these tachykinins and to examine expression during inflammation. PPT-I mRNA was detected by reverse transcription (RT)-polymerase chain reaction (PCR) in AM and brain (control) but not in peritoneal macrophages. Northern analysis showed that PPT-I mRNA was induced two- to fourfold by in vivo treatment of rats with intratracheal lipopolysaccharide (LPS) and in vitro after 4 h of exposure to LPS. This increase was inhibited by dexamethasone. In situ RT-PCR and immunocytochemistry further confirmed that AM express PPT-I mRNA and SP-like immunoreactivity, respectively, which was enhanced by LPS treatment. A 1.3-kb transcript consistent with PPT-I mRNA was detected by Northern analysis of bronchoalveolar lavage neutrophils. Therefore, rat AM express PPT-I mRNA that is upregulated in AM by LPS and is attenuated by dexamethasone. PPT-I mRNA was also detected in lung neutrophils.
Insights
Rat alveolar macrophages express preprotachykinin gene-I (PPT-I) mRNA, which encodes tachykinins. Lipopolysaccharide (LPS) upregulates this expression, while dexamethasone attenuates it, indicating a role in inflammation.
Area of Science:
- Immunology
- Neuroscience
- Molecular Biology
Background:
- Tachykinins, such as substance P (SP), are primarily found in neurons.
- Eosinophils are known to express tachykinins.
- The expression of tachykinins in macrophages, particularly alveolar macrophages (AM), is not well-established.
Purpose of the Study:
- To investigate whether rat alveolar macrophages (AM) express preprotachykinin gene-I (PPT-I) mRNA.
- To determine if PPT-I mRNA expression in AM is altered during inflammatory conditions.
- To examine the regulatory effects of lipopolysaccharide (LPS) and dexamethasone on PPT-I mRNA expression in AM.
Main Methods:
- Reverse transcription-polymerase chain reaction (RT-PCR) to detect PPT-I mRNA.
- Northern blot analysis to quantify PPT-I mRNA levels.
- In situ RT-PCR and immunocytochemistry to localize PPT-I mRNA and SP immunoreactivity in AM.
- In vivo and in vitro exposure of rats and AM to LPS.
- Treatment with dexamethasone.
Main Results:
- PPT-I mRNA was detected in rat AM and brain, but not in peritoneal macrophages.
- Intratracheal LPS administration and in vitro LPS exposure significantly upregulated PPT-I mRNA in AM (2-4 fold induction).
- Dexamethasone inhibited the LPS-induced increase in PPT-I mRNA expression.
- In situ methods confirmed PPT-I mRNA and SP-like immunoreactivity in AM, with enhanced expression after LPS treatment.
- PPT-I mRNA was also detected in neutrophils from bronchoalveolar lavage fluid.
Conclusions:
- Rat alveolar macrophages express PPT-I mRNA, encoding tachykinins.
- LPS upregulates PPT-I mRNA expression in AM during inflammation.
- Dexamethasone attenuates LPS-induced PPT-I mRNA expression in AM.
- These findings suggest a potential role for tachykinins produced by AM in lung inflammatory responses.