  The nucleus-nucleus interaction potentials in heavy-ion fusion reactions are
extracted from the microscopic time-dependent Hartree-Fock theory for mass
symmetric reactions $^{16}$O${}+^{16}$O, $^{40}$Ca${}+^{40}$Ca,
$^{48}$Ca${}+^{48}$Ca and mass asymmetric reactions $^{16}$O$ +^{40,48}$Ca,
$^{40}$Ca${}+^{48}$Ca, $^{16}$O+$^{208}$Pb, $^{40}$Ca+$^{90}$Zr. When the
center-of-mass energy is much higher than the Coulomb barrier energy,
potentials deduced with the microscopic theory identify with the frozen density
approximation. As the center-of-mass energy decreases and approaches the
Coulomb barrier, potentials become energy dependent. This dependence signs
dynamical reorganization of internal degrees of freedom and leads to a
reduction of the "apparent" barrier felt by the two nuclei during fusion of the
order of $2-3 %$ compared to the frozen density case. Several examples
illustrate that the potential landscape changes rapidly when the center-of-mass
energy is in the vicinity of the Coulomb barrier energy. The energy dependence
is expected to have a significant role on fusion around the Coulomb barrier.
