Lack of cAMP-response Element-binding Protein 1 in the Hypothalamus Causes Obesity

Abstract

The melanocortin system in the hypothalamus controls food intake and energy expenditure. Its disruption causes severe obesity in mice and humans. cAMP-response element-binding protein 1 (CREB1) has been postulated to play an important role downstream of the melanocortin-4 receptor (MC4R), but this hypothesis has never been confirmed in vivo. To test this, we generated mice that lack CREB1 in SIM1-expressing neurons, of the paraventricular nucleus (PVN), which are known to be MC4R-positive. Interestingly, CREB1⌬SIM1 mice developed obesity as a result of decreased energy expenditure and impairment in maintaining their core body temperature and not because of hyperphagia, defining a new role for CREB1 in the PVN. In addition, the lack of CREB1 in the PVN caused a reduction in vasopressin expression but did not affect adrenal or thyroid function. Surprisingly, MC4R function tested pharmacologically was normal in CREB1 ⌬SIM1 mice, suggesting that CREB1 is not required for intact MC4R signaling. Thus CREB1 may affect other pathways that are implicated in the regulation of body weight.The melanocortin 4 receptor (MC4R) 2 is widely expressed in the central nervous system, including a number of sites that contribute to coordinated control of body weight (1-3). The essential role of the MC4R is evident from the presence of severe obesity in both MC4R knock-out mice and in humans with naturally occurring mutations (4, 5). These mutations cause increased food intake and decreased energy expenditure (4, 6, 7). One key site of MC4R expression is the paraventricular nucleus of the hypothalamus (PVN) (1-3). The PVN is an area that regulates several neuroendocrine, behavioral, and autonomic functions, especially food intake and energy expenditure (8 -11). It has been implicated in the regulation of body weight as re-expression of MC4R in the PVN of mice on a null background rescues the obese phenotype (12). Mutations in the SIM1 (single-minded 1) gene, a transcription factor that controls development of the PVN, lead to the development of obesity in humans and mice, further implicating the PVN as a key regulator of body weight (13-17).The MC4R is known to signal through G s ␣, which in turn activates adenylyl cyclase, leading to increased intracellular levels of cAMP (1, 3, 18). Elevated cAMP levels induce phosphorylation and activation of the transcription factor cAMP-response element-binding protein (CREB1) through increased activity of protein kinase A, or PKA (19 -22). The importance of this pathway in body weight regulation in vivo is highlighted by the fact that constitutive activation of PKA is associated with leanness (23). The phosphorylation of CREB1 leads to the activation of CREB target gene expression (24,25). CREB signaling is complicated by the fact that a number of related transcription factors including cAMP-response element modulator (CREM) and activating transcription factor 1 are also phosphorylated by PKA and can compensate for CREB1 in its absence. Although activating transcription factor 1 is not thought t...

Gsα Deficiency in the Paraventricular Nucleus of the Hypothalamus Partially Contributes to Obesity Associated with Gsα Mutations

“…This may be relevant to humans as obesity in the absence of hyperphagia was documented in a child with a maternal G s ␣ mutation (5). Consistent with our findings, PVN-specific deletion of cAMP-response element binding protein 1, a downstream target of G s ␣, also leads to obesity with reduced energy expenditure in the absence of hyperphagia (23). PVN is an important site for regulation of food intake by MC4R (15,18).…”

Effects of A-CREB, a dominant negative inhibitor of CREB, on the expression of c-fos and other immediate early genes in the rat SON during hyperosmotic stimulation in vivo

“…Moreover, Iwasaki et al (1997) showed that the dominant negative CREB, KCREB, could partially block this increased expression. However, a recent in vivo study by Chiappini et al (2011) showed that while VP production was impaired in the PVN of CREB knockout mice, it was not impaired in the SON of these mice. Their conclusion is consistent with our result that blocking CREB in the SON in vivo does not change vasopressin expression.…”

Ventromedial hypothalamus–specific Ptpn1 deletion exacerbates diet-induced obesity in female mice

“…To delete Ptpn1, the gene encoding PTP1B, specifically in SF-1 neurons, mice expressing Cre recombinase under control of the Sf1 promoter ( Images were obtained using a Zeiss LSM 510 Meta Confocal Microscope at low and high magnifications (×10, ×20, and ×63 (57). To analyze data collected by indirect calorimetry, we followed recommendations established previously (54).…”

“…Serial coronal 20 to 30 μm-thick sections through the rostrocaudal extent of the hypothalamus were cut on a sliding freezing microtome (Leica SM2010R; Leica Microsystems); every fourth section was collected, placed in cryoprotectant solution (30% w/v ethylene glycol, 20% w/v glycerol, 50% w/v formaldehyde), and stored at -20°C until processed for immunohistochemistry or immunofluorescence (see below). Sections containing the VMH (bregma -1.20 to -2.22 mm) were analyzed by immunohistochemistry, as described (57,58). Immunostaining was performed using rabbit polyclonal pAKT (S473 D9E; 1:50; Cell Signaling Technology) and pFOXO1 (#28280, 1:50; Cell Signaling Technology) antibodies, based on previous publications (52,59).…”