TTF-1, a Homeodomain-containing Transcription Factor, Participates in the Control of Body Fluid Homeostasis by Regulating Angiotensinogen Gene Transcription in the Rat Subfornical Organ

Abstract

In recent years, it has become increasingly evident that angiotensins synthesized in the brain contribute to regulating body fluid homeostasis. Although angiotensinogen, the unique angiotensin precursor, is produced in the brain, the factors that regulate its gene expression remain unknown. We recently found that TTF-1, a homeodomain-containing transcription factor essential for the development of the fetal diencephalon, is postnatally expressed in discrete areas of the hypothalamus. We now report that the subfornical organ, an important site of angiotensinogen synthesis, is an extrahypothalamic site of TTF-1 expression. Double in situ hybridization histochemistry demonstrated the presence of TTF-1 mRNA in angiotensinogen-producing cells of the rat subfornical organ. RNase protection assays showed that TTF-1 and angiotensinogen mRNA levels are simultaneously increased in the subfornical organ by water deprivation. The angiotensinogen promoter contains seven presumptive TTF-1 binding motifs, four of which are recognized by the TTF-1 homeodomain. In the C6 glioma cell line, TTF-1 transactivates the angiotensinogen promoter in a dose-dependent manner. This transactivation is abolished by deletion of the TTF-1 binding motif at ؊125. Intracranial administration of an antisense TTF-1 oligodeoxynucleotide decreased angiotensinogen mRNA in the subfornical organ and dramatically reduced the animal's water intake while increasing urine excretion. Moreover, plasma arginine vasopressin content was decreased by the same treatment. These results demonstrate a novel role for TTF-1 in the regulation of body fluid homeostasis, exerted via the transactivational control of angiotensinogen synthesis in the subfornical organ.The control of body fluid volume and blood pressure is a critical homeostatic process required for normalcy of the internal environment and for the preservation of life. Many studies have demonstrated that the renin-angiotensin system (RAS) 1 plays an important role in the regulation of fluid volume balance, blood pressure, and other related biological responses through the generation of angiotensin II (ANG II) (1). The existence of a brain RAS in addition to the peripheral RAS has also been established (2, 3). All components of the peripheral RAS have been found in the brain, most notably in the subfornical organ (SFO). The SFO is a circumventricular organ (CVO) of the lamina terminalis located at the top of the dorsal third ventricle (4). It is composed of fenestrated capillary loops in addition to glial cells, but in contrast to other CVOs such as the median eminence of the hypothalamus, it also contains neuronal cell bodies (1, 5). The SFO of rats contains high concentrations of angiotensinogen (AoGen) (6), the angiotensin precursor; renin-like activity (that converts AoGen to ANG I) (7); angiotensin-converting enzyme (which converts ANG I to ANG II) (8); the peptide ANG II (9); and AT 1 -type ANG II receptors (3). Thus, the SFO is not only a target for circulating ANG II, which exerts a potent dipsogenic ef...

Thyroid Transcription Factor-1 Facilitates Cerebrospinal Fluid Formation by Regulating Aquaporin-1 Synthesis in the Brain

“…We and others have reported that TTF-1 remains expressed in the discrete regions of the postnatal rat brain (15,16). More recently, we showed that TTF-1 is expressed in the subfornical organ where it regulates angiotensinogen synthesis (17).…”

“…The AS TTF-1 ODN used to disrupt TTF-1 synthesis (5Ј-GAC TCA TCG ACA TGA TTC GGC GTC-3Ј) was directed against the sequence surrounding the first ATG codon of TTF-1 mRNA as reported previously (17,18). As a control, a scrambled (SCR) sequence of identical base composition was used (5Ј-AGT CCT ACT CGG TAC GTA TGC AGC-3Ј).…”

“…Oligodeoxynucleotides C and C␤ were used as a positive and negative control, respectively (20). EMSA was performed as described previously (17,18), using the TTF-1 HD and oligonucleotides at final concentrations of 150 and 5 mM, respectively. Electrophoretically separated signals corresponding to the protein-bound and free DNA were quantitated with Multianalyst software.…”

Deletion of theTtf1Gene in Differentiated Neurons Disrupts Female Reproduction without Impairing Basal Ganglia Function

“…Loss of neuronal TTF1 perturbs expression of genes involved in the control of puberty TTF1 remains expressed after birth not only in hypothalamic neurons but also in ependymoglial cells lining the third ventricle (Lee et al, 2001) and circumventricular organs (Son et al, 2002), precluding the use of conventional gene targeting approaches to identify neuronal versus glial sites of TTF1 action. To circumvent this limitation, we bred mice carrying Ttf1 floxed alleles at the Ttf1 locus (Kusakabe et al, 2006) to transgenic mice in which Cre recombinase is expressed under the control of the synapsin I gene promoter (henceforth referred to as SynCre mice).…”

TTF-1/NKX2.1 up-regulates the in vivo transcription of nestin

“…A subset of precursor cells expressing TTF-1/NKX2.1 migrates tangentially from the medial ganglionic eminence of the ventral telencephalon to the developing striatum and to the developing cortical plate (Marìn and Rubenstein, 2001;Anderson et al, 2001). TTF-1/NKX2.1 expression in the adult persists in the hypothalamus and in the subfornical organ, a circumventricular organ of the third ventricle (Lee et al, 2001;Son et al, 2003). TTF-1/NKX2.1 homozygous mutant mice were born dead and lacked completely the thyroid gland and the lung parenchyma, the entire pituitary was missing, and extensive defects were found in the THE INTERNATIONAL JOURNAL OF DEVELOPMENTAL BIOLOGY www.intjdevbiol.com ventral region of the forebrain (Kimura et al, 1996).…”