PPARgamma inhibits GH synthesis and secretion and increases apoptosis of pituitary GH-secreting adenomas.
OBJECTIVE
The objective of the study was to evaluate the expression and functional activity of Peroxisome proliferator-activated receptor (PPAR) gamma in pituitary adenomas from 14 consecutive acromegalic patients and to establish its role in apoptosis.


METHODS
Fourteen consecutive acromegalic patients were enrolled in the study. Wistar-Furth rats were used for in vivo studies. Expression of PPARgamma was evaluated by RT-PCR and Western blot. Apoptosis and cell cycle were assessed by FACS analysis. The effects of PPARgamma ligands on transcriptional regulation of GH gene were evaluated by RT-PCR and electromobility shift assay.


RESULTS
PPARgamma was expressed in all human GH-secreting adenoma (GH-oma), in normal pituitary tissue samples (39+/-24% and 78+/-5% of immunostained nuclei respectively; P<0.0002; ANOVA), and in rat GH-secreting (GH3) cells. A PPRE-containing reporter plasmid transfected into GH3 cells was activated by ciglitazone or rosiglitazone (TZDs), indicating that PPARgamma was functionally active. Treatment of GH3 cells with TZDs increased apoptosis in a dose-dependent manner (P=0.0003) and arrested cell proliferation, reducing the number of cells in the S-phase (P<0.0001 vs untreated cells). TZDs increased the expression of TRAIL, leaving unaffected that of p53 and Bax. TZDs reduced GH concentrations in the culture media from 43.7+/-5.4 ng/ml to 2.1+/-0.3 ng/ml (P<0.0001) and in cell extracts (P<0.004). PPARgamma-RXRalpha heterodimers bound to GH promoter, inhibiting its activity and reducing GH mRNA levels (1.8 x 10(6) vs 5.7 x 10(6) transcripts respectively vs untreated cells; P<0.002). Subcutaneous GH-oma developed in rats injected with GH3 cells; tumor growth increased in placebo-treated rats and to a lesser extent in TZDs-treated animals (24.1+/-2.0 g, and 14.8+/-4.2 g respectively, P<0.03). Serum GH concentrations were lower in TZDs-treated rats than in controls (871+/-67 ng/ml vs 1.309+/-238 ng/ml; P<0.05).


CONCLUSIONS
The results of this study indicate that PPARgamma controls GH transcription and secretion as well as apoptosis and growth of GH-oma; thus, TZDs have the potential of a useful tool in the complex therapeutic management of acromegalic patients.
Bogazzi
Fausto
F
Department of Endocrinology and Metabolism, University of Pisa, 56124, Pisa, Italy. f.bogazzi@endoc.med.unipi.it
Ultimieri
Federica
F
Raggi
Francesco
F
Russo
Dania
D
Vanacore
Renato
R
Guida
Chiara
C
Viacava
Paolo
P
Cecchetti
Denise
D
Acerbi
Giovanni
G
Brogioni
Sandra
S
Cosci
Chiara
C
Gasperi
Maurizio
M
Bartalena
Luigi
L
Martino
Enio
E
D000236:Adenoma / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D017304:Annexin A5 / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology*; D002460:Cell Line; D053938:DNA Fragmentation; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D019382:Human Growth Hormone / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D051379:Mice; D008819:Mice, Nude; D041681:NIH 3T3 Cells; D010911:Pituitary Neoplasms / Q000378:metabolism* / Q000473:pathology; D011401:Promoter Regions, Genetic / Q000235:genetics; D051381:Rats; D011920:Rats, Inbred WF; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077154:Rosiglitazone; D045162:Thiazolidinediones / Q000494:pharmacology; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
D017304:Annexin A5; D008024:Ligands; D018160:Receptors, Cytoplasmic and Nuclear; D045162:Thiazolidinediones; D014157:Transcription Factors; D000077154:Rosiglitazone; D019382:Human Growth Hormone; C039671:ciglitazone