Exogenous spermine preserves mitochondrial bioenergetics via regulating Src kinase signaling in the spinal cord

Regulation of mitochondrial metabolism is becoming an important target in inhibiting necrosis and apoptosis following secondary spinal cord injury, and physiological compounds that reduce mitochondrial dysfunction are regarded as efficient protective reagents following injury. It has been demonstrated that spermine, a polyamine composed of four primary amines, may be taken up by a mitochondria-specific uniporter and may preserve mitochondrial bioenergetics, suggesting that it may be important in the pathophysiology of mitochondria. However, the protective mechanism has not yet been definitively clarified. In the present study, isolated spinal cord mitochondria were incubated with spermine to evaluate its physiological functions and Src kinase activities. The results revealed that spermine increased oxidative phosphorylation, attenuated mitochondrial swelling and maintained the membrane potential. An inhibitor of Src kinases, amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), markedly reduced the effects of spermine. However, inhibition of tyrosine phosphatases by vanadate led to marginal increases in the effects of spermine. Therefore, the present study hypothesized that tyrosine phosphorylation sites are present in the subunits of respiratory chains and mitochondrial permeability transition pore proteins, which may be modified via phosphorylation and dephosphorylation. Furthermore, spermine may upregulate the phosphorylation of Src kinases, and PP2 and vanadate conversely regulate Src phosphorylation. The results of the present study suggest that spermine is a strategic regulator within mitochondria that may activate Src kinases in the spinal cord, and tyrosine phosphorylation signaling is a primary regulatory pathway of mitochondrial metabolism.