Plasma proteomic profiles of bovine growth hormone transgenic mice as they age

Attenuation of the growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis results in extended lifespan in many organisms including mice. Conversely, GH transgenic mice have excess GH action and die prematurely. We have studied bovine (b) GH transgenic mice (n = 9) and their wild type (WT) littermates (n = 8) longitudinally and have determined several age-related changes. Compared to WT mice, bGH mice lost fat mass, became hypoglycemic and had lower insulin levels at older ages despite being hyperinsulinemic when young. To examine plasma protein differences in bGH mice relative to controls, samples at 2, 4, 8, 12 and 16 months of age were analyzed by two-dimensional gel electrophoresis followed by identification using mass spectrometry. We found several differences in plasma proteins of bGH mice compared to controls, including increased apolipoprotein E (five isoforms), haptoglobin (four isoforms) and mannose-binding protein-C (one out of three isoforms), and decreased transthyretin (six isoforms). In addition, clusterin (two out of six isoforms) and haptoglobin (four isoforms) were up-regulated in bGH mice as a function of age. Finally, alpha-2 macroglobulin (seven isoforms) was altered in an isoform-specific manner with two isoforms increased and two decreased in bGH mouse plasma compared to controls. In conclusion, identification of these proteins suggests that bGH mice exhibit an increased inflammatory state with an adverse lipid profile, possibly contributing to their diminished life expectancy. Also, these newly discovered plasma proteins may be indicative or 'biomarkers' of a shortened lifespan.