title: Stimulation of TM3 Leydig cell proliferation via GABA(A) receptors: a new role for testicular GABA.
abstract: The neurotransmitter gamma-aminobutyric acid (GABA) and subtypes of GABA receptors were recently identified in adult testes. Since adult Leydig cells possess both the GABA biosynthetic enzyme glutamate decarboxylase (GAD), as well as GABA(A) and GABA(B) receptors, it is possible that GABA may act as auto-/paracrine molecule to regulate Leydig cell function. The present study was aimed to examine effects of GABA, which may include trophic action. This assumption is based on reports pinpointing GABA as regulator of proliferation and differentiation of developing neurons via GABA(A) receptors. Assuming such a role for the developing testis, we studied whether GABA synthesis and GABA receptors are already present in the postnatal testis, where fetal Leydig cells and, to a much greater extend, cells of the adult Leydig cell lineage proliferate. Immunohistochemistry, RT-PCR, Western blotting and a radioactive enzymatic GAD assay evidenced that fetal Leydig cells of five-six days old rats possess active GAD protein, and that both fetal Leydig cells and cells of the adult Leydig cell lineage possess GABA(A) receptor subunits. TM3 cells, a proliferating mouse Leydig cell line, which we showed to possess GABA(A) receptor subunits by RT-PCR, served to study effects of GABA on proliferation. Using a colorimetric proliferation assay and Western Blotting for proliferating cell nuclear antigen (PCNA) we demonstrated that GABA or the GABA(A) agonist isoguvacine significantly increased TM3 cell number and PCNA content in TM3 cells. These effects were blocked by the GABA(A) antagonist bicuculline, implying a role for GABA(A) receptors. In conclusion, GABA increases proliferation of TM3 Leydig cells via GABA(A) receptor activation and proliferating Leydig cells in the postnatal rodent testis bear a GABAergic system. Thus testicular GABA may play an as yet unrecognized role in the development of Leydig cells during the differentiation of the testicular interstitial compartment.
authors.affiliation: Anatomisches Institut der Ludwig-Maximilians-Universität München, Biedersteinerstr,29, D-80802 München, Germany. geigerseder@web.de
authors.forename: Christof
authors.initials: C
authors.lastname: Geigerseder
authors.forename: Richard F G
authors.initials: RF
authors.lastname: Doepner
authors.forename: Andrea
authors.initials: A
authors.lastname: Thalhammer
authors.forename: Annette
authors.initials: A
authors.lastname: Krieger
authors.forename: Artur
authors.initials: A
authors.lastname: Mayerhofer
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D004789:Enzyme Activation / Q000502:physiology; D018755:GABA Agonists / Q000494:pharmacology; D050485:GABA Plasma Membrane Transport Proteins; D005968:Glutamate Decarboxylase / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D007539:Isonicotinic Acids / Q000494:pharmacology; D007985:Leydig Cells / Q000166:cytology* / Q000201:enzymology / Q000502:physiology; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D051379:Mice; D008807:Mice, Inbred BALB C; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000378:metabolism / Q000502:physiology*; D013737:Testis / Q000737:chemistry* / Q000166:cytology / Q000201:enzymology; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
chemical_list: D002352:Carrier Proteins; D018755:GABA Agonists; D050485:GABA Plasma Membrane Transport Proteins; C546241:Gabra1 protein, mouse; C546270:Gabrb3 protein, mouse; D007527:Isoenzymes; D007539:Isonicotinic Acids; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D018809:Proliferating Cell Nuclear Antigen; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1; C015300:isoguvacine