Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disease marked by the progressive degeneration and loss of upper motor neurons (MNs) in the motor cortex as well as lower MNs in the brainstem and spinal cord (van Es et al., 2017). The clinical symptoms are characterized by gradual muscle weakness and atrophy, often resulting in respiratory failure and death within 3–5 years after the onset of symptoms (Oskarsson et al., 2018). Most ALS cases are believed to arise from an interplay between genetic and environmental factors (Vasta et al., 2022). In ALS, over 30 genes or genetic loci have been identified with mutations, including superoxide dismutase 1 (SOD1), C9orf72, OPTN, fused in sarcoma (FUS), TDP43, and others (Saberi et al., 2015). The pathogenesis of ALS remains incompletely understood, and various studies indicate its involvement in neuroinflammation, mitochondrial dysfunction, abnormal RNA metabolism, endoplasmic reticulum stress, oxidative stress, and impaired axonal transport (Mejzini et al., 2019). The G93A mutation in human superoxide dismutase 1 (hSOD1) demonstrates complex pathogenic mechanisms associated with ALS (Gurney et al., 1994). Although extensive research has been carried out to investigate the pathophysiological mechanisms underlying ALS, the development of effective therapeutic strategies continues to present a formidable challenge.

The X-linked inhibitor of apoptosis protein (Xiap) belongs to the IAP family (Duckett et al., 1996). The function of Xiap involves the prevention of cell apoptosis by inhibiting caspase-3/−7/−9 activation (Kang et al., 2010; Xu et al., 2019a, Xu et al., 2019b). Moreover, Xiap is involved in regulating the process of necroptosis (Wicki et al., 2016). Research suggests that Xiap expression was decreased in transgenic mouse models of ALS. Overexpression of Xiap has clearly demonstrated the beneficial effects in ALS (Wootz et al., 2006). It decreased apoptosis in SH-SY5Y neuronal cells (Garrity-Moses et al., 2006).

Death-associated protein kinase 1 (DAPK1) is a 160 kDa serine/threonine protein kinase (Bialik and Kimchi, 2006; Deiss et al., 1995). It is implicated in several biological processes, including cell apoptosis, inflammation, cell cycle regulation, autophagy, and oxidative stress (Elkamhawy et al., 2022; Luo et al., 2011; Xiong et al., 2018; Yoo et al., 2012; Zhang et al., 2022). It has been found that DAPK1 is widely expressed in the cerebral cortex and hippocampus (Sakagami and Kondo, 1997; Yamamoto et al., 1999). Functional genetic variants of DAPK1 are correlated with an elevated risk of Alzheimer's Disease (AD) (Xu et al., 2019a, Xu et al., 2019b). DAPK1 overexpression enhances tau protein stability by phosphorylating multiple sites linked to AD (Singh et al., 2016). Furthermore, in the transient brain ischemia, an upregulation of DAPK1 induces neuronal apoptosis (Yamamoto et al., 1999). Research suggests that elevated DAPK1 may promote neuronal death by enhancing the function of “calcium-activated death signaling proteins”(Lai et al., 2011). Together, these studies suggest that knocking down DAPK1 would exhibit neuroprotective effects in ALS.

In this study, we observed an increase of DAPK1 in ALS models. Emerging evidence from prior investigations has demonstrated that DAPK1 functions as a negative modulator of Xiap (Ding et al., 2017; Ishak et al., 2014), whereas Xiap promotes motor neuron survival. Based on this, we postulated that targeted suppression of DAPK1 might confer neuroprotective benefits in ALS pathogenesis. Our results revealed that elevated DAPK1 expression exacerbated motor neuron apoptosis through its regulatory inhibition of XIAP-mediated survival pathways. Conversely, the knockdown of DAPK1 demonstrated a neuroprotective role by preventing motor neuron apoptosis. Notably, the protective effect was weakened by the application of a Xiap inhibitor. These findings collectively indicate that the beneficial role of knocking down DAPK1 in ALS MNs is mediated through the Xiap signaling.