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 proSAAS 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.
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S Wei, Y Feng, FY Che, H Pan, N Mzhavia, LA Devi, AA McKinzie, N Levin, WG Richards, and LD Fricker
Marta Lantero Rodriguez, Maaike Schilperoort, Inger Johansson, Elin Svedlund Eriksson, Vilborg Palsdottir, Jan Kroon, Marcus Henricsson, Sander Kooijman, Mia Ericson, Jan Borén, Claes Ohlsson, John-Olov Jansson, Malin C Levin, Patrick C N Rensen, and Åsa Tivesten
Brown adipose tissue (BAT) burns substantial amounts of mainly lipids to produce heat. Some studies indicate that BAT activity and core body temperature are lower in males than females. Here we investigated the role of testosterone and its receptor (the androgen receptor; AR) in metabolic BAT activity in male mice. Castration, which renders mice testosterone deficient, slightly promoted the expression of thermogenic markers in BAT, decreased BAT lipid content, and increased basal lipolysis in isolated brown adipocytes. Further, castration increased the core body temperature. Triglyceride-derived fatty acid uptake, a proxy for metabolic BAT activity in vivo, was strongly increased in BAT from castrated mice (4.5-fold increase vs sham-castrated mice) and testosterone replacement reversed the castration-induced increase in metabolic BAT activity. BAT-specific AR deficiency did not mimic the castration effects in vivo and AR agonist treatment did not diminish the activity of cultured brown adipocytes in vitro, suggesting that androgens do not modulate BAT activity via a direct, AR-mediated pathway. In conclusion, testosterone is a negative regulator of metabolic BAT activity in male mice. Our findings provide new insight into the metabolic actions of testosterone.