Mitochondrial functions are coordinated with their dynamic behaviour due to the balance of the processes of fusion and fission that determines overall mitochondrial morphology. The imbalance in these processes can result in defects associated with lipid and glucose metabolism.

This study aimed to analyze the effects of chronic overfeeding with high fat diet (HFD) rich in saturated or polyunsaturated fatty acids on mitochondrial function, morphology and dynamics.

Three groups of rats were fed, for 6 weeks, standard diet (N rats), HFD rich in lard (40% J/J, L rats), or fish oil (40% J/J, F rats).

Liver steatosis, lipid content, and apoptosis were determined. Mitochondrial function was assessed by measuring oxidation rates and proton conductance. Mitochondrial contents of protein involved in fusion (MFN2) and fission (DRP1) were determined by western blot. The morphological features of mitochondria were analyzed by electron microscopy (EM).

L rats showed the highest lipid contents. F mitochondria exhibited higher oxidation rates and proton conductance compared to L ones. The EM revealed alteration in size, shape, matrix density and in number and feature of cristae in F and L rats. DRP1content was > in L than F, while MFN2 < in L than F. Apoptosis was more evident in L rats than in N and F.

Mitochondrial ultrastructural alterations and the higher trend to the fission in L rats seemed to be associated to an higher degree of lipid accumulation and rate of apoptosis in liver.