CLUH maintains functional mitochondria and translation in motoneuronal axons and prevents peripheral neuropathy

Abstract

Transport and local translation of mRNAs in distal axonal compartments are essential for neuronal viability. Local synthesis of nuclear-encoded mitochondrial proteins protects mitochondria from damage during their long journey along the axon, however the regulatory factors involved are largely unknown. Here, we show that CLUH, a cytosolic protein that binds mRNAs encoding mitochondrial proteins, is essential for preventing axonal degeneration of spinal motoneurons and maintaining motor behavior in the mouse. We demonstrate that CLUH is enriched in the growth cone of developing spinal motoneurons and is required for their growth. The absence of CLUH affects the abundance of target mRNAs and the corresponding mitochondrial proteins more prominently in axons, leading to ATP deficits specifically in the growth cone. CLUH binds ribosomal subunits, translation initiation and ribosome recycling components, and preserves axonal translation. Overexpression of the ribosome recycling factor ABCE1 rescues the growth cone and translation defects in CLUH-deficient motoneurons. In conclusion, we demonstrate a role for CLUH in mitochondrial quality control and translational regulation in axons, which are essential for their development and long-term integrity and function.

Proteomic analysis of the TDP-43-associated insoluble fraction from NEFH-TDP-43 mouse brain suggests sustained stress granule formation, CLUH granule recruitment and impaired mitochondrial metabolism

“…The positive effect of uridine supplementation on translation in CLUH KO motoneurons (Zaninello et al, 2023), supports the notion of stress-related feedback loops leading to neuronal starvation and ATP crisis. From a therapeutic perspective, uridine can substitute for ribose in the PPP, potentially sparing the RNA (Skinner et al, 2023).…”

“…We speculate that the SG response and the CLUH granule response would prevent SG resolution, as this is an ATP dependent process (Jain et al, 2016). The positive effect of uridine supplementation on translation in CLUH KO motoneurons, supports this notion (Zaninello et al, 2023). From a therapeutic perspective, uridine can substitute for ribose in the PPP, potentially sparing the RNA (Skinner et al, 2023).…”

“…CLUH is the mRNA binding protein responsible for mitochondrial transport of nuclear encoded mitochondrial mRNA (Gao et al, 2014; Schatton et al, 2017; Wakim et al, 2017). CLUH is also required for neuronal development and motor neurone integrity (Zaninello et al, 2023). In response to glucose and amino acid starvation-induced stress, CLUH and its bound mRNAs form large RNP granules (Pla-Martin et al, 2020; Yang et al, 2022).…”

“…However, it can use branched chain amino acids and ketone bodies, specifically leucine and β-hydroxybutyrate respectively (Divakaruni et al, 2017; Jensen et al, 2020). Although speculative, CLUH recruitment into the TDP-43-associated SG fraction would diminish its physiological role and contribute to the excessive impairment in mitochondrial function, as well as axonal and NMJ degradation seen in ALS (Altman et al, 2021; Zaninello et al, 2023). Identifying the point during ALS disease progression when CLUH is recruited to TDP-43-associated granules will be important to understand mechanisms of disease progression and potentially provide an opportunity for therapeutic intervention.…”

“…These inverse changes in the functional networks from insoluble brain and soluble MN samples is consistent with the role of RBPs and RNA granules in the transport of mRNA for local translation in distal axons of MNs (Altman et al, 2021; Piol et al, 2023). For example, CLUH has a specific role in the transport and stability of nuclear encoded mitochondrial mRNA in MNs and maintenance of the NMJ (Gao et al, 2014; Schatton et al, 2017; Zaninello et al, 2023). The recruitment of CLUH and CLUH target mRNA to the insoluble TDP-43-associated SG fraction in the brain may result in depletion of these same molecules in the functional soluble component in distal axons of MNs.…”