Survival in sporadic ALS is associated with lower p62 burden in the spinal cord

Amyotrophic Lateral Sclerosis: Focus on Cytoplasmic Trafficking and Proteostasis

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal motor neuron disease characterized by the pathological loss of upper and lower motor neurons. Whereas most ALS cases are caused by a combination of environmental factors and genetic susceptibility, in a relatively small proportion of cases, the disorder results from mutations in genes that are inherited. Defects in several different cellular mechanisms and processes contribute to the selective loss of motor neurons (MNs) in ALS. Prominent among these is the accumulation of aggregates of misfolded proteins or peptides which are toxic to motor neurons. These accumulating aggregates stress the ability of the endoplasmic reticulum (ER) to function normally, cause defects in the transport of proteins between the ER and Golgi, and impair the transport of RNA, proteins, and organelles, such as mitochondria, within axons and dendrites, all of which contribute to the degeneration of MNs. Although dysfunction of a variety of cellular processes combines towards the pathogenesis of ALS, in this review, we focus on recent advances concerning the involvement of defective ER stress, vesicular transport between the ER and Golgi, and axonal transport.

Heterogeneous nuclear ribonucleoprotein D - an understudied subfamily affected in sporadic TDP-43 proteinopathies

Despite the recognition that heterogeneous nuclear ribonucleoproteins (hnRNPs) modulate TDP-43 and can limit aberrant splicing events to compensate for TDP-43 loss, their role in TDP-43 proteinopathies remains poorly understood and studies in patient tissue are lacking. This study assesses seven heterogeneous nuclear ribonucleoproteins from the A/B, C, D and H subfamilies in two cortical regions implicated in early TDP-43 dysfunction versus late TDP-43 dysfunction in sporadic amyotrophic lateral sclerosis and/or frontotemporal lobar degeneration. Our results reveal significant nuclear loss of hnRNPD, hnRNPC and hnRNPA1 in the frontal cortex of frontotemporal lobar degeneration compared to amyotrophic lateral sclerosis but not in the motor cortical neurons or Betz cells of amyotrophic lateral sclerosis cases. Cytoplasmic co-occurrence was observed between hnRNPA1 and hnRNPC but not with phosphorylated TDP-43 (pTDP-43). Interestingly, nuclear hnRNPD loss associated with increasing cytoplasmic pTDP-43, highlighting an understudied subfamily in sporadic TDP-43 proteinopathies. In summary, this study identifies the nuclear loss of hnRNPD, C and A1 in a predilection brain region of TDP-43 in frontotemporal lobar degeneration compared to amyotrophic lateral sclerosis cases without significant pTDP-43 in this region. This highlights the need for further investigation into the involvement of these heterogeneous nuclear ribonucleoproteins in disease pathogenesis and potential to serve as modulatory targets and/or proximal markers of TDP-43 dysfunction in sporadic TDP-43 proteinopathies.

TDP-43 regulates LC3ylation in neural tissue through ATG4B cryptic splicing inhibition

Amyotrophic lateral sclerosis (ALS) is an adult-onset motor neuron disease with a mean survival time of three years. The 97% of the cases have TDP-43 nuclear depletion and cytoplasmic aggregation in motor neurons. TDP-43 prevents non-conserved cryptic exon splicing in certain genes, maintaining transcript stability, including ATG4B, which is crucial for autophagosome maturation and Microtubule-associated proteins 1A/1B light chain 3B (LC3B) homeostasis. In ALS mice (G93A), Atg4b depletion worsens survival rates and autophagy function. For the first time, we observed an elevation of LC3ylation in the CNS of both ALS patients and atg4b-/- mouse spinal cords. Furthermore, LC3ylation modulates the distribution of ATG3 across membrane compartments. Antisense oligonucleotides (ASOs) targeting cryptic exon restore ATG4B mRNA in TARDBP knockdown cells. We further developed multi-target ASOs targeting TDP-43 binding sequences for a broader effect. Importantly, our ASO based in peptide-PMO conjugates show brain distribution post-IV administration, offering a non-invasive ASO-based treatment avenue for neurodegenerative diseases.

Molecular aspects of optic nerve autophagy in glaucoma

The optic nerve consists of the glia, vessels, and axons including myelin and axoplasm. Since axonal degeneration precedes retinal ganglion cell death in glaucoma, the preceding axonal degeneration model may be helpful for understanding the molecular mechanisms of optic nerve degeneration. Optic nerve samples from these models can provide information on several aspects of autophagy. Autophagosomes, the most typical organelles expressing autophagy, are found much more frequently inside axons than around the glia. Thus, immunoblot findings from the optic nerve can reflect the autophagy state in axons. Autophagic flux impairment may occur in degenerating optic nerve axons, as in other central nervous system neurodegenerative diseases. Several molecular candidates are involved in autophagy enhancement, leading to axonal protection. This concept is an attractive approach to the prevention of further retinal ganglion cell death. In this review, we describe the factors affecting autophagy, including nicotinamide riboside, p38, ULK, AMPK, ROCK, and SIRT1, in the optic nerve and propose potential methods of axonal protection via enhancement of autophagy.