D. Bell et Bj. Mcdermott, Contribution of de novo protein synthesis to the hypertrophic effect of IGF-1 but not of thyroid hormones in adult ventricular cardiomyocytes, MOL C BIOCH, 206(1-2), 2000, pp. 113-124
Background: Enhanced expression of IGF-1 occurs in left ventricular hypertr
ophy (LVH) associated with systemic hypertension. Cardiac dysfunction accom
panied by LVH is also observed in hyperthyroidism. Objective: to assess the
relative contributions of de novo protein synthesis and attenuated protein
degradation to increased protein mass associated with cardiomyocyte hypert
rophy elicited by IGF-1 and thyroid hormones (tri-iodo thyronine T-3, and l
-thyroxine T-4), respectively. Methods: total mass of protein, and both the
incorporation, and removal of previously incorporated l-U-C-14-phenylalani
ne, indices of protein synthesis and degradation, respectively, were assess
ed in quiescent adult rat ventricular cardiomyocytes maintained in shortter
m culture, and corrected for DNA content, as a index of cell number. Result
s: IGF-1 (1 pM-100 nM) increased cell protein significantly, maximally at 1
nM and by 38% above basal value after 24 h. T-3 (10 pM-2 mu M) and T-4 (10
pM-2 mu M) increased cell protein significantly maximally at 1 mu M and by
33.2 and 30.5%, respectively, above basal value. IGF-1 (less than or equal
to 10 pM), T-3 (10 pM-2 mu M) and T-4 (10 pM-2 mu M) did not increase inco
rporation of l-U-C-14-phenylalanine above basal values. IGF-1 (100 pM-100 n
M) increased incorporation of radiolabel significantly maximally at 100 nM
and by 56%. T-4 (100 pM) and IGF-1 (10 pM), concentrations that did not sti
mulate de novo protein synthesis, attenuated the degradation of radiolabell
ed protein by 13.6 and 11.8%, respectively, compared to control values afte
r 48 h. Conclusion: These data indicate that the acute hypertrophic respons
e to (i) thyroid hormones cannot be attributed to initiation of de novo pro
tein synthesis; (ii) IGF-1 comprises two components; the response elicited
by IGF-1 (<10 pM) is independent of, while the response elicited by IGF-1 (
>100 pM) is due to de novo protein synthesis.