Expression changes of Rhodopsin and recoverin in MNU-induced photoreceptor degeneration in rats

AIM: To investigate the time-effect relationship between the expression of rhodopsin and recoverin and photoreceptor damage induced by N-nethl-N-nitrosourea(MNU). METHODS: Thirty-six 7-week old Sprague-Dawley(SD)rats were intraperitoneally injected with MNU(60mg/kg)and were put to death by dislocation of cervical vertebra 6, 12, 24h; 3, 7d after injection(6 per group), respectively. As a control, six rats were injected with phosphate buffer saline(PBS)5mL/kg and sacrificed on d3 after injection. The degree of photoreceptor apoptosis was detected by HE staining, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling(TUNEL)and transmission electron microscope(TEM)in the right eyes. The mRNA expressions of rhodopsin and recoverin were detected different time after injection by Western blot and immunohistochemical method in the left eyes. RESULTS: The dissolution of photoreceptor nucleus and apoptosis body were first perceived at 12h by TEM; most of cells at outer nuclear layer were presented positive reaction. The apoptotic index reached peak(29.7%±2.3%)at 24h which was coincided with the observation of TEM. The results of immunohistochemistry displayed that rhodopsin and recoverin were on a declining curve with time extension. Furthermore, the results of Western blot indicated that rhodopsin had dramatic decline at 6h after injection(P<0.05), and extremely significant difference comparing to control group after 12h(P<0.01); while recoverin dramatic declined at 12h, and extremely significant difference after 24h(P<0.01). CONCLUSION: 60mg/kg MNU intraperitoneally injection one-time may specifically induce photoreceptor apoptosis, The mechanism of down-regulation of rhodopsin and recoverin may be related to the selected apoptosis of photoreceptors.