Retinoids and activation of PKC induce tissue-type plasminogen activator expression and storage in human astrocytes.
BACKGROUND
Emerging data demonstrate important roles for tissue-type plasminogen activator (t-PA) in the central nervous system (CNS). In contrast to endothelial cells, little is known about the regulation of t-PA gene expression and secretion in astrocytes.


OBJECTIVE
The aims of the present study were to investigate whether t-PA gene expression is regulated by retinoids and the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) in human astrocytes, and to study whether t-PA is stored and subject to regulated release from these cells, as with endothelial cells.


METHODS
Native human astrocytes were treated with RA and/or PMA. mRNA was quantified by real-time RT-PCR and protein secretion determined by ELISA. Intracellular t-PA immunoreactivity in astrocytes was examined by immunocyto- and histochemistry.


RESULTS
RA and/or PMA induced a time-dependent increase in t-PA mRNA and protein levels in astrocytes, reaching 10-fold after combined treatment. This was associated with increased amounts of t-PA storage in intracellular granular structures. Both forskolin and histamine induced regulated release of t-PA. The presence of t-PA in reactive astrocytes was confirmed in human brain tissue.


CONCLUSIONS
These data show that RA and PKC activation induce a strong up-regulation of t-PA expression in astrocytes, and increased intracellular storage pools. Moreover, a regulated release of t-PA can be induced from these cells. This raises the possibility that astrocytes contribute to the regulation of extracellular t-PA levels in the CNS.
Hultman
K
K
Institute of Neuroscience and Physiology, Department of Clinical Neuroscience and Rehabilitation, the Sahlgrenska Academy at University of Gothenburg, Department of Clinical Genetics, Sahlgrenska University Hospital, Gothenburg, Sweden.
Tjärnlund-Wolf
A
A
Fish
R J
RJ
Wilhelmsson
U
U
Rydenhag
B
B
Pekny
M
M
Kruithof
E K O
EK
Jern
C
C
D001253:Astrocytes / Q000378:metabolism*; D001923:Brain Chemistry; D004789:Enzyme Activation / Q000187:drug effects; D005786:Gene Expression Regulation; D006801:Humans; D007700:Kinetics; D011493:Protein Kinase C / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D012176:Retinoids / Q000494:pharmacology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010959:Tissue Plasminogen Activator / Q000235:genetics* / Q000378:metabolism
D012333:RNA, Messenger; D012176:Retinoids; D011493:Protein Kinase C; D010959:Tissue Plasminogen Activator; D013755:Tetradecanoylphorbol Acetate