Possible mechanism for the decrease of mitochondrial aspartate aminotransferase activity in ischemic and hypoxic rat retinas

AbstractGlutamate is believed to be an excitatory amino acid neurotransmitter in the retina. Enzymes for glutamate metabolism, such as glutamate dehydrogenase, ornithine aminotransferase, glutaminase, and aspartate aminotransferase (AAT), exist mainly in the mitochondria. The abnormal increase of intracellular calcium ions in ischemic retinal cells may cause an influx of calcium ions into the mitochondria, subsequently affecting various mitochondrial enzyme activities through the activity of mitochondrial calpain. As AAT has the highest level of activity among enzymes involved in glutamate metabolism, we investigated the change of AAT activity in ischemic and hypoxic rat retinas and the protection against such activity by calpain inhibitors. We used normal RCS (rdy+/rdy+) rats. For the in vivo studies, we clamped the optic nerve of anesthetized rats to induce ischemia. In the in vitro studies, the eye cups were incubated with Locke’s solution saturated with 95% N2/5% CO2. The activity of cytosolic AAT (cAAT) was about 20% of total activity, whereas mitochondrial AAT (mAAT) was about 75% in rat retina. Ninety minutes of ischemia or hypoxia caused a 20% decrease in mAAT activity, whereas cAAT activity remained unchanged. To examine the contribution of intracellular calcium ions to the degradation of mAAT, we used Ca2+-free Locke’s solution containing 1 mM EGTA, ryanodine (Ca2+ channel blocker), and thapsigargin (Ca2+-ATPase inhibitor). In the present study, thapsigargin in Ca2+-free Locke’s solution, but not ryanodine in this solution, was found to prevent AAT degradation. AAT degradation was also prevented by calpain inhibitors (Ca2+-dependent protease inhibitor) such as calpeptin at 1 nM, 10 nM, 0.1 μM, 1 μM and 10 μM, and by calpain inhibitor peptide, but not by other protease inhibitors (10 μM leupeptin, pepstatin, chymostatin). Additionally, we determined the subcellular localization of calpain activity and examined the change of calpain activity in ischemic rat retinas. Our results suggest that decreased activity of mAAT in ischemic and hypoxic rat retinas might be evoked by the degradation by calpain-catalyzed proteolysis in mitochondria

Effects of soil compaction on the seedlings growth and ectomycorrhizal fungal community in hybrid larch

Soil physical composition is one of the fundamental factors regulating plant growth as well as soil microbes. For the rising expectation to optimize techniques of forestry machinery for sustainable forest managements in Japan, it is essential to assess the effects of soil compaction caused by machinery running on seedlings of afforestation tree species. Since most afforestation tree species interact with soil microbes, such as the symbiosis with ectomycorrhizal fungi, the effects of soil compaction would extend to the relationship between these microbes and planted seedlings. We evaluated the effects of soil compaction on growth and ectomycorrhizal fungi in hybrid larch seedlings. The experimental site was established with no compacted and compacted plots in the Sapporo experimental forest site of Hokkaido University, where two-year-old seedlings were planted. At compacted plots, the surface hardness was 25 kg cm-2 and the bulk density was 1.1 g cm-3. Height growth of seedlings was significantly suppressed, and the dry weight was decreased 50% at compacted plots than that of seedlings grown at uncompacted plots. The dominant group of associated ectomycorrhizal fungi was changed by soil compaction. Our data showed that the effect of soil compaction can suppress growth of seedlings and shape the specific ectomycorrhizal fungal community

Evaluating Soil-Root Interaction of Hybrid Larch Seedlings Planted under Soil Compaction and Nitrogen Loading

Although compacted soil can be recovered through root development of planted seedlings, the relationship between root morphologies and soil physical properties remain unclear. We investigated the impacts of soil compaction on planted hybrid larch F-1(Larix gmeliniivar.japonicaxL. kaempferi, hereafter F-1) seedlings with/without N loading. We assumed that N loading might increase the fine root proportion of F(1)seedlings under soil compaction, resulting in less effects of root development on soil recovery. We established experimental site with different levels of soil compaction and N loading, where two-year-old F(1)seedlings were planted. We used a hardness change index (HCI) to quantify a degree of soil hardness change at each depth. We evaluated root morphological responses to soil compaction and N loading, focusing on ectomycorrhizal symbiosis. High soil hardness reduced the total dry mass of F(1)seedlings by more than 30%. Significant positive correlations were found between HCI and root proportion, which indicated that F(1)seedling could enhance soil recovery via root development. The reduction of fine root density and its proportion due to soil compaction was observed, while these responses were contrasting under N loading. Nevertheless, the relationships between HCI and root proportion were not changed by N loading. The relative abundance of the larch-specific ectomycorrhizal fungi under soil compaction was increased by N loading. We concluded that the root development of F(1)seedling accelerates soil recovery, where N loading could induce root morphological changes under soil compaction, resulting in the persistent relationship between root development and soil recovery

Relationship between the Intake of n-3 Polyunsaturated Fatty Acids and Depressive Symptoms in Elderly Japanese People: Differences According to Sex and Weight Status

n-3 polyunsaturated fatty acids (PUFAs) have been shown to have preventive effects against depression. In this study, we aimed to investigate the associations between the intake of n-3 PUFAs and depression among people according to sex and weight status. We utilized cross-sectional data from the Shika study in Japan. The study was conducted between 2013 and 2016. Data were collected from adults older than 65 years. Invitation letters were distributed to 2677 individuals, 2470 of whom participated in the study (92.3%). We assessed depressive states using the Japanese short version of the Geriatric Depression Scale (GDS-15). We assessed the intake of n-3 PUFAs using the validated food frequency questionnaire. One thousand six hundred thirty-three participants provided data, among which 327 (20.0%) exhibited depressive symptoms. When we performed the stratified analysis by sex and weight status, there were significant inverse relationships between total n-3 PUFAs, individual n-3 PUFAs, and n-3/n-6 PUFAs ratio and depressive symptoms in overweight/obese females. No correlations were observed between n-3 PUFAs intake and depressive states in males. The results demonstrated a relationship between n-3 PUFAs deficiencies and depressive states, particularly in overweight/obese females. Dietary modifications may help to prevent depressive symptoms in overweight/obese females