Possible mechanisms of Leukoagglutinin induced apoptosis in human cells in vitro

Lectin-induced oxidative stress in human platelets

Previously we have shown that wheat germ agglutinin (WGA) and, with minor potency, Phaseolus vulgaris agglutinin (PHA), but not lens culinarian agglutinin (LCA), induce platelet aggregation, through the PLCƴ2 activation by the concerted action of src/syk and PI3K/BTK pathways. In this study, we have investigated platelet oxidative stress induced by lectins. Several parameters indicative of oxidative stress, such as reactive oxygen species (ROS), superoxide anion, lipid peroxidation and the efficiency of the aerobic metabolism, have been measured. It was found that ROS, superoxide anion formation and lipid peroxidation are significantly increased upon platelet treatment with WGA and PHA while LCA is ineffective. WGA is always more effective than PHA in all experimental conditions tested. In addition, the involvement of NADPH oxidase 1, syk and PI3K in oxidative stress induced by WGA and PHA has been shown. Concerning the lectins effect on aerobic metabolism, WGA and PHA, but not LCA, act as uncoupling agents, determining an increase of oxygen consumption and a decrease of ATP synthesis, with a consequent decrease of P/O value. These results are confirmed by the impairment of platelets proton gradient formation, evaluated by membrane potential, in platelets treated with WGA and PHA. In conclusion lectins, especially WGA, induce oxidative stress in platelets and decrease energy availability through modifications of membrane structure leading to the inefficiency of the aerobic machinery that steers platelets toward death as suggested by the decreased metabolic activity of platelets and the increased lactic dehydrogenase release.

Aerobic endurance training status affects lymphocyte apoptosis sensitivity by induction of molecular genetic adaptations

Apoptosis is a genetically regulated form of programmed cell death which promotes the elimination of potentially detrimental immune cells. However, exercise-associated apoptosis is thought to induce a temporarily decline of the adaptive immune competence in the early post-exercise period. The purpose of the present study was to investigate if the aerobic endurance training status affects the sensitivity of human peripheral blood lymphocytes towards different types of apoptosis inducers and secondly, if this is mediated by the modulation of apoptosis-associated proteins and microRNAs. Collected at resting conditions, isolated lymphocytes of endurance trained athletes (ET) and healthy untrained subjects were either exposed to phytohemagglutinin-L (PHA-L), hydrogen peroxide (H₂O₂), or dexamethasone (DEX) as apoptosis inducer. Results revealed no significant differences between ET and UT in terms of lymphocyte apoptosis immediately following isolation as determined by flow cytometry using annexin V staining. After 24 h of ex vivo cultivation, lymphocytes of ET showed a reduced sensitivity to PHA-L-induced lymphocyte apoptosis which was accompanied by a noticeably up-regulation of the prominent apoptosis inhibitor genes X-linked inhibitor of apoptosis (XIAP) and Cyclin dependent kinase inhibitor 1B (CDKN1B) as analyzed by quantitative real-time PCR. Moreover, a trend was observed for the suppression of the corresponding pro-apoptotic miR-221. Lymphocyte apoptosis in control, H₂O₂ and DEX treated cells was not affected by aerobic endurance training status. However, distinct molecular signatures could be identified in un-treated control samples characterized by a counterbalanced modulation of pro- and anti-apoptotic mediators in ET. The results of the current study suggest that lymphocytes adapt to repetitive endurance exercise training by promoting lymphocyte homeostasis and increasing their resistance to apoptosis. This could be based on an up-regulation of anti-apoptotic proteins and a reduction in pro-apoptotic microRNAs which together tightly regulate the genetically defined apoptotic pathways governed by the type of apoptosis stimuli. Thus, the lymphocytes of endurance-trained athletes may be primed to counteract the transient immune suppression post-exercise.

The molecular mechanisms involved in lectin-induced human platelet aggregation

We have compared the effect of three legume lectins, wheat germ agglutinin (WGA), Phaseolus vulgaris agglutinin (PHA) and Lens culinaris agglutinin (LCA), on the function of human platelets. We have found that WGA is more active than PHA in stimulating platelet activation/aggregation, while LCA has no effect. Studies on the mechanisms involved show that WGA and PHA induce phosphorylation/activation of PLCγ2 and increase [Ca2+]i. For the first time, it has been shown that Src/Syk pathway, the adapter protein SLP-76 and the exchange protein VAV, participate in the PLCγ2 activation by these lectins. Moreover WGA and PHA stimulate the PI3K/AKT pathway. PI3K, through its product phosphatidylinositol-3,4,5-trisphosphate activates Bruton's tyrosine kinase (BTK) and contributes to PLCγ2 activation. In conclusion, our findings suggest that PLCγ2 activation induced by WGA and PHA is regulated by Src/Syk and by PI3K/BTK pathways through their concerted action.

Posterior fossa decompression in Chiari I improves denervation of the paraspinal muscles

OBJECTIVE

To investigate whether posterior fossa decompression (PFD) could improve denervation of the paraspinal muscles in patients with Chiari I malformation (CMI).

BACKGROUND

Paraspinal muscle denervation is one of the essential elements in the pathophysiology of CMI/syringomyelia-related scoliosis. Although PFD has been widely used for managing CMI, whether denervation of the paraspinal muscles may benefit from this neurosurgical procedure remains ambiguous. Bax and Bcl-2 are two regulators of apoptosis that are closely related to the innervation status of skeletal muscles, and denervation is associated with upregulated Bax and downregulated Bcl-2.

METHODS

Thirty-seven patients who underwent PFD and subsequent deformity correction for CMI-associated scoliosis were enrolled. Biopsy specimens were obtained from bilateral erector spinae muscles during both procedures with an average interval of 6.5 months. The biopsy site was located within the spinal innervation region involved by the syrinx and near the level of upper instrumented vertebra. The expression levels of Bax and Bcl-2 as well as histological features of the muscle fibres were examined at the two time points.

RESULTS

After PFD, the mRNA level of antiapoptotic Bcl-2 was elevated by 178% and 260% in the convex and concave muscles, respectively, with a coincident decrease of 69% and 73% for proapoptotic Bax at the corresponding sites (p<0.001). Consistent with the mRNA data, the Bcl-2 protein in the paraspinal muscles was increased by 75% on the convex and by 169% on the concave side following PFD. For Bax protein, decreases of 45% and 52% were detected in the convex and concave muscles, respectively (p<0.001). On average, these changes led to a 60% decrease in the Bax/Bcl-2 ratio, suggesting reduced apoptotic signalling and improved innervation of the paraspinal muscles. Histologically, the specimens demonstrated improvements in denervation-associated changes of the muscle fibres following PFD, with the number of atrophic and necrotic/degenerated fibres decreasing significantly from 6.7 and 8.5 before surgery to 3.2 (p=0.012) and 4.2 (p<0.001) after surgery, respectively.

CONCLUSION

In patients with CMI, treatment with PFD led to a decrease in the Bax/Bcl-2 ratio at both the mRNA and protein levels, indicating an attenuated susceptibility to apoptotic cell death. These data, coupled with the observed improvements in histopathological features of the myofibres, suggest that PFD in Chiari I ameliorates denervation of the paraspinal muscles.