Obesity and diabetes in transgenic mice expressing proSAAS

Abstract

ProSAAS is a neuroendocrine peptide precursor that potently inhibits prohormone convertase 1 in vitro. To explore the function of proSAAS and its derived peptides, transgenic mice were created which express proSAAS using the beta-actin promoter. The body weight of transgenic mice was normal until approximately 10-12 weeks, and then increased 30-50% over wild-type littermates. Adult transgenic mice had a fat mass approximately twice that of wild-type mice, and fasting blood glucose levels were slightly elevated. In the pituitary, the levels of several fully processed peptides in transgenic mice were not reduced compared with wild-type mice, indicating that the proSAAS transgene did not affect prohormone convertase 1 activity in this tissue.Because the inhibitory potency of proSAAS-derived peptides towards prohormone convertase 1 is much greater in the absence of carboxypeptidase E activity, the pro-SAAS transgene was also expressed in carboxypeptidase E-deficient Cpe fat/fat mice. Although the transgenic mice were born in the expected frequency, 21 of 22 proSAAS transgenic Cpe fat/fat mice died between 11 and 26 weeks of age, presumably due to greatly elevated blood glucose. The levels of several pituitary peptides were significantly reduced in the proSAAS transgenic Cpe fat/fat mice relative to non-transgenic Cpe fat/fat mice, suggesting that the transgene inhibited prohormone convertase 1 in these mice. Taken together, these results are consistent with a role for proSAAS-derived peptides as neuropeptides that influence body weight independently of their function as inhibitors of prohormone convertase 1.

Examination of the rate of peptide biosynthesis in neuroendocrine cell lines using a stable isotopic label and mass spectrometry

“…However, the finding that a cell line expressing low levels of proSAAS (line 7) is not affected to the same degree as lines expressing relatively high amounts of proSAAS (lines 5 and 41) implies that proSAAS is not very potent in vivo. These results are similar to those observed for proSAAS-expressing transgenic mice; mice with a twofold increase in the level of proSAAS do not show significant defects in the levels of processed neuropeptides (Wei et al 2004). Previous studies have established that the key peptide processing enzymes have pH optima in the acidic 5-6 range (Fricker and Snyder 1982;Eipper et al 1991;Greene et al 1992;Seidah and Chretien 1998a,b;Zhou et al 1999).…”

GPR171 is a hypothalamic G protein-coupled receptor for BigLEN, a neuropeptide involved in feeding

“…supports a role for the BigLEN-GPR171 system in regulating these functions. This idea is supported by the finding that third ventricular injections of antibodies to BigLEN affect food intake in mice that can be augmented by GPR171 knockdown and by previous studies which found that overexpression or deletion of proSAAS produces alterations in body weight (10,11). The identification of GPR171 as the receptor for BigLEN provides insights into these mechanisms but also may provide a target for therapeutic modulation of food intake and metabolism.…”

Relative quantitation of peptides in wild‐type and Cpefat/fat mouse pituitary using stable isotopic tags and mass spectrometry

“…36,39 However, the pituitary is sufficiently rich in neuropeptides that affinity purification is not necessary for this tissue. 40 Recently, it was reported that neuropeptides could be detected in extracts of hypothalami from animals killed by focused microwave irradiation; 41 hence it should be possible to apply the technique used in the present study to the analysis of brain peptides.…”