METTL3-dependent RNA m6A dysregulation contributes to neurodegeneration in Alzheimer’s disease through aberrant cell cycle events

Background N6-methyladenosine (m6A) modification of RNA influences fundamental aspects of RNA metabolism and m6A dysregulation is implicated in various human diseases. In this study, we explored the potential role of RNA m6A modification in the pathogenesis of Alzheimer disease (AD). Methods We investigated the m6A modification and the expression of m6A regulators in the brain tissues of AD patients and determined the impact and underlying mechanism of manipulated expression of m6A levels on AD-related deficits both in vitro and in vivo. Results We found decreased neuronal m6A levels along with significantly reduced expression of m6A methyltransferase like 3 (METTL3) in AD brains. Interestingly, reduced neuronal m6A modification in the hippocampus caused by METTL3 knockdown led to significant memory deficits, accompanied by extensive synaptic loss and neuronal death along with multiple AD-related cellular alterations including oxidative stress and aberrant cell cycle events in vivo. Inhibition of oxidative stress or cell cycle alleviated shMettl3-induced apoptotic activation and neuronal damage in primary neurons. Restored m6A modification by inhibiting its demethylation in vitro rescued abnormal cell cycle events, neuronal deficits and death induced by METTL3 knockdown. Soluble Aβ oligomers caused reduced METTL3 expression and METTL3 knockdown exacerbated while METTL3 overexpression rescued Aβ-induced synaptic PSD95 loss in vitro. Importantly, METTL3 overexpression rescued Aβ-induced synaptic damage and cognitive impairment in vivo. Conclusions Collectively, these data suggested that METTL3 reduction-mediated m6A dysregulation likely contributes to neurodegeneration in AD which may be a therapeutic target for AD.

Neuronal Cell Cycle Re-Entry Enhances Neuropathological Features in App NLF Knock-In Mice

Background: Aberrant cell cycle re-entry is a well-documented process occurring early in Alzheimer’s disease (AD). This is an early feature of the disease and may contribute to disease pathogenesis. Objective: To assess the effect of forced neuronal cell cycle re-entry in mice expressing humanized Aβ, we crossed our neuronal cell cycle re-entry mouse model with App NLF knock-in (KI) mice. Methods: Our neuronal cell cycle re-entry (NCCR) mouse model is bitransgenic mice heterozygous for both Camk2a-tTA and TRE-SV40T. The NCCR mice were crossed with App NLF KI mice to generate NCCR-App NLF animals. Using this tet-off system, we triggered NCCR in our animals via neuronal expression of SV40T starting at 1 month of age. The animals were examined at the following time points: 9, 12, and 18 months of age. Various neuropathological features in our mice were evaluated by image analysis and stereology on brain sections stained using either immunofluorescence or immunohistochemistry. Results: We show that neuronal cell cycle re-entry in humanized Aβ plaque producing App NLF KI mice results in the development of additional AD-related pathologies, namely, pathological tau, neuroinflammation, brain leukocyte infiltration, DNA damage response, and neurodegeneration. Conclusion: Our findings show that neuronal cell cycle re-entry enhances AD-related neuropathological features in App NLF mice and highlight our unique AD mouse model for studying the pathogenic role of aberrant cell cycle re-entry in AD.

Eltrombopag directly inhibits BAX and prevents cell death

The BCL-2 family protein BAX has essential activity in mitochondrial regulation of cell death. While BAX activity ensures tissue homeostasis, when dysregulated it contributes to aberrant cell death in several diseases. During cellular stress BAX is transformed from an inactive cytosolic conformation to a toxic mitochondrial oligomer. Although the BAX transformation process is not well understood, drugs that interfere with this process are useful research tools and potential therapeutics. Here, we show that Eltrombopag, an FDA-approved drug, is a direct inhibitor of BAX. Eltrombopag binds the BAX trigger site distinctly from BAX activators, preventing them from triggering BAX conformational transformation and simultaneously promoting stabilization of the inactive BAX structure. Accordingly, Eltrombopag is capable of inhibiting BAX-mediated apoptosis induced by cytotoxic stimuli. Our data demonstrate structure-function insights into a mechanism of BAX inhibition and reveal a mechanism for Eltrombopag that may expand its use in diseases of uncontrolled cell death.