Mitochondrial quality control failure is frequently observed in neurodegenerative diseases. The detection of damaged mitochondria by stabilization of PTEN-induced kinase 1 (PINK1) requires transport of Pink1 messenger RNA (mRNA) by tethering it to the mitochondrial surface. Here, we report that inhibition of AMP-activated protein kinase (AMPK) by activation of the insulin signalling cascade prevents Pink1 mRNA binding to mitochondria. Mechanistically, AMPK phosphorylates the RNA anchor complex subunit SYNJ2BP within its PDZ domain, a phosphorylation site that is necessary for its interaction with the RNA-binding protein SYNJ2. Notably, loss of mitochondrial Pink1 mRNA association upon insulin addition is required for PINK1 protein activation and its function as a ubiquitin kinase in the mitophagy pathway, thus placing PINK1 function under metabolic control. Induction of insulin resistance in vitro by the key genetic Alzheimer risk factor apolipoprotein E4 retains Pink1 mRNA at the mitochondria and prevents proper PINK1 activity, especially in neurites. Our results thus identify a metabolic switch controlling Pink1 mRNA localization and PINK1 activity via insulin and AMPK signalling in neurons and propose a mechanistic connection between insulin resistance and mitochondrial dysfunction.

Established disease models have helped unravel the mechanistic underpinnings of pathological phenotypes in Parkinson’s disease (PD), the second most common neurodegenerative disorder. However, these discoveries have been limited to relatively simple cellular systems and animal models, which typically manifest with incomplete or imperfect recapitulation of disease phenotypes. The advent of induced pluripotent stem cells (iPSCs) has provided a powerful scientific tool for investigating the underlying molecular mechanisms of both familial and sporadic PD within disease-relevant cell types and patient-specific genetic backgrounds. Overwhelming evidence supports mitochondrial dysfunction as a central feature in PD pathophysiology, and iPSC-based neuronal models have expanded our understanding of mitochondrial dynamics in the development and progression of this devastating disorder. The present review provides a comprehensive assessment of mitochondrial phenotypes reported in iPSC-derived neurons generated from PD patients’ somatic cells, with an emphasis on the role of mitochondrial respiration, morphology, and trafficking, as well as mitophagy and calcium handling in health and disease. Furthermore, we summarize the distinguishing characteristics of vulnerable midbrain dopaminergic neurons in PD and report the unique advantages and challenges of iPSC disease modeling at present, and for future mechanistic and therapeutic applications.

Motor axon regeneration following peripheral nerve injury is critical for motor recovery but therapeutic interventions enhancing this are not available. We conduct a phenotypic screen on human motor neurons and identified blebbistatin, a non-muscle myosin II inhibitor, as the most effective neurite outgrowth promotor. Despite its efficacy in vitro, its poor bioavailability limits in vivo application. We, therefore, utilize a blebbistatin analog, NMIIi2, to explore its therapeutic potential for promoting axon regeneration. Local NMIIi2 application directly to injured axons enhances regeneration in human motor neurons. Furthermore, following a sciatic nerve crush injury in male mice, local NMIIi2 administration to the axonal injury site facilitates motor neuron regeneration, muscle reinnervation, and functional recovery. NMIIi2 also promotes axon regeneration in sensory, cortical, and retinal ganglion neurons. These findings highlight the therapeutic potential of topical NMII inhibition for treating axon damage.

A central role in mitochondrial quality control is played by the Parkinson-related mitochondrial kinase PINK1, whose mRNA is transported in neurons by mitochondrial hitch- hiking. Using a live-cell imaging assay for the translation of the PINK1 precursor, we show that local translation of PINK1 requires a concerted interplay between mitochondria and the ER in neurons. For efficient translation, the Pink1 mRNA needs to relocate to ribosomes located near endolysosomes and the ER. The ER membrane-tethered chaperone DNAJB6 then shields the PINK1 precursor on transit to mitochondria following the ER-SURF pathway. Loss of DNAJB6 hence leads to persistence of ER/endolysosome-associated PINK1 precursor stores and failure of mitophagy upon mitochondrial damage.

Motor axon regeneration following peripheral nerve injury is critical for motor recovery but therapeutic interventions enhancing this are not available. We conducted a phenotypic screen on human motor neurons and identified blebbistatin, a non-muscle myosin II inhibitor, as the most effective neurite outgrowth promotor. Despite its efficacy in vitro, its poor bioavailability limits in vivo application. We, therefore, utilized a blebbistatin analog, NMIIi2, to explore its therapeutic potential for promoting axon regeneration. Local NMIIi2 application directly to injured axons enhanced regeneration in human and mouse motor neurons in vitro. Furthermore, following a sciatic nerve crush injury in mice, local NMIIi2 administration to the axonal injury site facilitated motor axon outgrowth, muscle reinnervation, and functional recovery. NMIIi2 also promoted axon regeneration in sensory, cortical, and retinal ganglion neurons. These findings highlight the therapeutic potential of topical NMII inhibition for treating axon damage.