Weiliang Xia

SIRT2 activity is required for the survival of C6 glioma cells

SIRT2 is a tubulin deacetylase, which can play either detrimental or beneficial roles in cell survival under different conditions. While it has been suggested that reduced SIRT2 expression in human gliomas may contribute to development of gliomas, there has been no study that directly determines the effects of decreased SIRT2 activity on the survival of glioma cells. In this study we applied both pharmacological and molecular approaches to determine the roles of SIRT2 in the survival of glioma cells. Our studies, by conducting such assays as flow cytometry-based Annexin V assay and caspase-3 immunostaining, have indicated that decreased SIRT2 activity leads to apoptosis of C6 glioma cells by caspase-3-dependent pathway. Our experiments have further shown that reduced SIRT2 activity produces necrosis of C6 glioma cells. Moreover, our study applying SIRT2 siRNA has also shown that decreased SIRT2 leads to both necrosis and apoptotic changes of C6 glioma cells. Collectively, our study has provided novel evidence indicating that SIRT2 activity plays a key role in maintaining the survival of glioma cells, and that reduced SIRT2 activity can induce both necrosis and caspase-3-dependent apoptosis of C6 glioma cells. These results have also suggested that inhibition of SIRT2 might become a novel therapeutic strategy for gliomas.

NAD+ metabolism and NAD(+)-dependent enzymes: promising therapeutic targets for neurological diseases.

Numerous studies have indicated that four interacting factors, including oxidative stress, mitochondrial alterations, calcium dyshomeostasis and inflammation, play crucial pathological roles in multiple major neurological diseases, including stroke, Alzheimers disease (AD) and Parkinsons disease (PD). Increasing evidence has also indicated that NAD(+) plays important roles in not only mitochondrial functions and energy metabolism, but also calcium homeostasis and inflammation. The key NAD(+)-consuming enzyme--poly(ADP-ribose) polymerase-1 (PARP-1) and sirtuins--have also been shown to play important roles in cell death and aging, which are two key factors in the pathology of multiple major age-dependent neurological diseases: PARP-1 plays critical roles in both inflammation and oxidative stress-induced cell death; and sirtuins also mediate the process of aging, cell death and inflammation. Thus, it is conceivable that increasing evidence has suggested that NAD(+) metabolism and NAD(+)-dependent enzymes are promising targets for treating a number of neurological illnesses. For examples, the key NAD(+)-dependent enzymes SIRT1 and SIRT2 have been indicated to strongly affect the pathological changes of PD and AD; PARP-1 inhibition can profoundly reduce the brain injury in the animal models of multiple neurological diseases; and administration of either NAD(+) or nicotinamide can also decrease ischemic brain damage. Future studies are necessary to further investigate the roles of NAD+ metabolism and NAD⁺-dependent enzymes in neurological diseases, which may expose novel targets for treating the debilitating illnesses.

Therapeutic Potential of Intranasal Delivery of Drugs and Cells for Stroke and Other Neurological Diseases

Although numerous studies have suggested the pathological mechanisms underlying stroke-induced brain damage, most clinical trials on the drug treatment of ischemic stroke have been unsuccessful. One of the key obstacles for establishing effective therapies for stroke and other neurological diseases is the blockage of entrance of drugs and therapeutic cells into the brain by the blood-brain barriers (BBB). A number of studies have suggested that intranasal drug delivery is a promising approach for effectively delivering drugs into the brain by bypassing the BBB. There may be at least one intracellular transport-mediated route and two extracellular transport-mediated routes for the nose-to-brain delivery. Recent studies have further suggested that intranasal delivery may also deliver therapeutic cells into the brain more effectively and less invasively compared to traditional approaches. However, multiple key questions regarding intranasal drug and cell delivery for treating neurological disorders remain unanswered. Future studies on intranasal delivery in humans as well as the mechanisms underlying the intranasal delivery may suggest novel biological mechanisms and markedly enhance our capacity of treating stroke and other neurological diseases.

Antioxidant protects blood-testis barrier against synchrotron radiation X-ray-induced disruption

Synchrotron radiation (SR) X-ray has wide biomedical applications including high resolution imaging and brain tumor therapy due to its special properties of high coherence, monochromaticity and high intensity. However, its interaction with biological tissues remains poorly understood. In this study, we used the rat testis as a model to investigate how SR X-ray would induce tissue responses, especially the blood-testis barrier (BTB) because BTB dynamics are critical for spermatogenesis. We irradiated the male gonad with increasing doses of SR X-ray and obtained the testicles 1, 10 and 20 d after the exposures. The testicle weight and seminiferous tubule diameter reduced in a dose- and time-dependent manner. Cryosections of testes were stained with tight junction (TJ) component proteins such as occludin, claudin-11, JAM-A and ZO-1. Morphologically, increasing doses of SR X-ray consistently induced developing germ cell sloughing from the seminiferous tubules, accompanied by shrinkage of the tubules. Interestingly, TJ constituent proteins appeared to be induced by the increasing doses of SR X-ray. Up to 20 d after SR X-ray irradiation, there also appeared to be time-dependent changes on the steady-state level of these protein exhibiting differential patterns at 20-day after exposure, with JAM-A/claudin-11 still being up-regulated whereas occludin/ZO-1 being down-regulated. More importantly, the BTB damage induced by 40 Gy of SR X-ray could be significantly attenuated by antioxidant N-Acetyl-L-Cysteine (NAC) at a dose of 125 mg/kg. Taken together, our studies characterized the changes of TJ component proteins after SR X-ray irradiation, illustrating the possible protective effects of antioxidant NAC to BTB integrity.