Mouse Immp21Gene Mutation And Aging Related Central Nervous System Disorders

Objective and backgroundMitochondria are involved in cellular energy metabolism, regulation of apoptosis,intracellular calcium homeostasis and other important cellular functions organizers.Meanwhile, as the primary location of in vivo generation of superoxide, the normalfunction of mitochondria is essential to ensure that DNA, proteins and lipids are exemptedfrom oxidative damage. Mutations in mitochondrial genes tend to have a huge change onthe phenotype thus resulting transgenic animals die in the embryonic stage, which makesthe study of the role of mitochondrial dysfunction in aging, neurodegenerative and otheraspects of reproductive almost impossible in live animals.Mitochondrial membrane peptidase (Imp) is a signal peptidase complex, the mainfunctions of it is hydrolysis the signal peptide of membrane proteins localized in themitochondrial membrane to ensure that they are properly positioned in themitochondria.The mice Imp2mutation caused deletion of this gene product, which willaffect the cytochrome C1and glycerol phosphate dehydrogenase2in the innermitochondrial membrane, and a direct result of this is the accumulation of intracellularreactive oxygen species, consuming intracellular nitric oxide, glutathione and other anti-oxides, leave the cells under oxidative stress.Since this mutation is not enough in causingrapid death or cell apoptosis, Immp2l mutant mouse strains can be used to observe theeffects of high level mitochondrial reactive oxygen species have in vivo and explore itspathophysiology.It has been observed that, Immp2l mutant mice have less body weight andsubcutaneous fat comparing with age and sex matched wild-type animals. Previous studiessuggest that reactive oxygen species may act by regulating the brain NPY/AgRP andPOMC neurons, which can affect feeding behavior, but the exact mechanism is unknown.Nitric oxide has a known effect that it can stimulate food intake in several species. So herewe suppose that reactive oxygen species may interact with nitric oxide and affect feedingbehavior. Around this conjecture, feeding activity on Immp2l mutant mice were observedand measured and calculated according to energy consumption, distribution ofsubcutaneous fat, brain nitrate/nitrite oxidation, cGMP concentration and NO passwayrelated gene expression levels, trying to get the evidence of reactive oxygen species affect feeding behavior by interacting with NO signaling pathways.Similarly, we try to use the same mechanism to explain ataxia, muscle abnormalities,humpback and other age-related neurodegenerative diseases observed in Immp2l mutantmice. Although mitochondrial reactive oxygen and free radicals in aging and age-relateddiseases has accumulated in vitro evidence already, but in vivo studies are still lacking andthere is little clues of its specific mechanism. That’s why we designed another researchrelated to Immp2l mutant mice mitochondrial dysfunction, free oxygen radicals, nitricoxide and nerve damage to clarify the possible mechanism.Methods and ResultsExperiments and results of this study are as follows:First part，to illustrate the relationship between Immp2l mutant mice’s age-relatedcerebellar degeneration and superoxide and function of NO in this process. It was fount outthat Immp2l mutant mice had an early onset of ataxia, humpback and stretch reflexabnormalities than wild-type mice. After analyzing the histological analysis of thecerebellum, NO synthase expression, cells peroxidation levels and granulosa cell apoptosis,mouse cerebellar granule cells were isolated and cultured to compared mitochondrialrespiratory chain function and energy metabolism, super oxide and cGMP levels. Theresults confirmed that in the mutant mitochondria there’s high level superoxide andincreased NO synthase expression, NO downstream signaling molecules cGMP wasreduced. For cerebellum tissue, there was increased cerebellar granule cell apoptosis inaged mice, granule cell layer was thinner than the wild type and cerebellum weight wassmaller, explaining the mutant mice’s early onset of ataxia, humpback and abnormalstretch reflex expression.Second part，to find out whether Immp2l mutant mouse weight loss in mice andsubcutaneous fat reduction is a result of decreased appetite caused food intake. In thissection, feeding activity of both groups of mice were observed and measured. Energyconsumption rate, subcutaneous fat distribution, hypothalamus tissue nitrate/nitrite levels,cGMP levels and NO pathway gene expression levels were compared. It was confirmedthat Immp2l mutant mice food intake is lower than wild-type mice’s, after exclusion otherfactors that can affect body weight and fat deposition, such as increased energyconsumption, increased locomotor activity and abnormal hormone levels in metabolism,counted in the facts that decreased hypothalamus nitrate/nitrite and cGMP concentration and increased NO synthase expression, we believe that reactive oxygen species reduced thebioavailability of NO in the hypothalamus, which affected the feeding center in thehypothalamus and led to decreased food intake.Conclusion1, Decreased food intake in Immp2lTg (Tyr) OVE979mice led to weight loss and reductionof subcutaneous fat deposition, and superoxide reduced the bioavailability of NO offeeding center is an important cause of reduced food intake.2, Early onset of Immp2lTg (Tyr) OVE979mice’s neurodegeneration diseases is due tocerebellar granule cells caused by oxidative stress.3, Immp2lTg (Tyr) OVE979mice have excess mitochondrial oxygen free radicalsgeneration but no energy metabolism defects, so they can be used as a good in vivo animalmodel in the research of oxidative stress in the pathogenesis of CNS.