In the current study, the correlation between the enzymes declared to be involved in lamin degradation was evaluated to define which enzymes were responsible for laminopathy in AD. Among four lamin-degrading enzymes (caspase 6, cathepsin L, and granzymes A and B), only two of them participated in the laminopathy signaling pathway triggered by Aβ aggregation (caspase 6 and cathepsin L). Based on the Pearson correlation results, caspase 3 and cathepsin B suggested activated caspase 6, while cathepsin L activated independently through a separate signaling pathway. Finding a drug that inhibited both pathways simultaneously could be a potential treatment against laminopathy in AD.
In the Angel et al. 2020 study, the caspase 6 knockout 5xFAD model of AD demonstrated that the expression of caspase 3 was decreased in the group with caspase 6 knockout. Meanwhile, the level of caspase 3 correlated with axonal loss in the hippocampus (21). This fact suggested that the caspase 3 and 6 expressions are correlated to each other, which in the current study, the correlation was observed in the normal samples. In addition, it was mentioned that caspase 6 could be activated by the induction of caspase 3 (22). Moreover, substitution mutation of the 73rd aminoacid of the caspase 6 reduces the efficacy of caspase 6 in acting on lamin A/C and α-Tubulin, which caused a protective factor against hippocampal atrophy (23). In our study there was a strong negative correlation between the expression level of lamin A/C and caspase 6, highlighting the role of caspase 6 in lamin A/C degradation causing neural apoptosis.
Besides, the pathology activity of cathepsin B in AD was mentioned in the Hook et al. study. Accordingly, it was reported that cathepsin B involved in the memory deficit and enhancement in the production of pyroglutamate-Aβ. Correspondingly, cathepsin B knockout in the hAβPP695 Wt mice model improves cognitive function (7). In the current drug discovery, cathepsin L inhibitor and caspase inhibitor X had a high binding affinity with cathepsin B (7.8 and 8.1 Kcal/mol, respectively). The caspase inhibitor x was formerly recommended as a potent inhibitor of caspase 8, 3, and 7 in the Binding Database (https://www.bindingdb.org/). Nonetheless, the inhibitory effect of this compound on cathepsin L has not been mentioned.
In the study conducted by Nagakannan et al., it was stated that reactive oxygen species (ROS) activated cathepsin L, leading to cell apoptosis. In addition, lysosomal membrane permeabilization as the result of ROS, activated cathepsin B, subsequently influences caspase 3, leading to cell apoptosis (24). In another study, the ROS was linked to the activation of Thioredoxin which influences the activity of caspase 6 causing lamin b1 degradation (22). In addition, in the Slee and Martin study, it was clearly demonstrated that caspase 3 activated caspase 6, leading to lamin A degradation (25). These results depicted two main signaling pathways leading to the laminopathy; one with the involvement of cathepsin B, caspase 3 and 6, the other with the participation of cathepsin L. Based on the result of the Pearson correlation presented in Fig. 3, indicating the opposite expression level of the caspase 6 and cathepsin L, it can be concluded that there are two different signaling pathways in lamin degradation, one mediated by caspase 6 and the other mediated by cathepsin L.
In the study conducted by Ramasamy et al. 2016 it was declared that Aβ could induce lamin degradation independent from caspase activity (26). In addition, in the Hossain et al. 2023 research, it was mentioned that the Aβ aggregation induced an increase in calcium concentration resulting in activating cathepsin L. Moreover, the calcium ion could activate another pathway mediated by caspase 6. However, the result of the study highlighted a difference in the lamin’s fragment as the result of cathepsin L and caspase 6 activity (27). The results of these two studies were in line with our findings and highlighted the role of cytoplasmic calcium as a mediator of activation of two laminopathy pathways. One of our study limitations was the MD simulation which led us to use coarse-grained instead of all-atom simulation due to the servers analyzing time. Moreover, in the current study, the in vitro/vivo assessment was not implemented, since the inhibitors were not accessible to be purchased for this project. Further studies are suggested to perform an all-atom simulation or in vitro/vivo assessment on the effect of these inhibitors on the proteases involved in the laminopathy in AD.