Sequalae and reversal of age-dependent alterations in mitochondrial dynamics via autophagy enhancement in reprogrammed human neurons.

Cryoelectron tomography reveals an age-related decline in mitoribosomes that contributes to T cell dysfunction in older individuals.

Mitochondrial dysfunction drives T cell aging in mice. Yet, due to fundamental differences in T cell aging mechanisms between species, whether human T cells exhibit similar mitochondrial alterations remains unclear, with existing evidence often conflicting. Using cryoelectron tomography, we resolved the structure and spatial organization of mitochondrial ribosomes in primary human CD8+ T cells under physiological conditions. Comparative analysis with human aging models revealed an age-related reduction in mitoribosome abundance and in higher-order mitoribosome organization, which is necessary for cooperative translation. Defective mitochondrial translation suppressed cytosolic ribosomal protein expression, thereby limiting mitochondrial biogenesis. The consequent reduction in mitochondrial mass induced an aged T cell phenotype characterized by compromised memory phenotypes and proliferative capacity. Enhancing mitochondrial translation via overexpression of the mitoribosomal component Mrps5 reversed aged T cell phenotypes in a mouse model of viral infection or tumor. Together, our findings provide nanoscale-resolution views of internal mitochondrial structures in situ, revealing an age-related loss of mitoribosomes. This loss contributes to mitochondrial dysfunction and the subsequent decline in T cell function observed in older individuals. Restoring mitochondrial translation may therefore represent a strategy for mitigating T cell dysfunction in the aging population.

The organellar biology of aging: A mitochondrial vantage

More research in the field may unravel the mechanistic details of the organellar crosstalk that works in concert with classical aging pathways to sustain aging progression, which may help promote healthier aging.

Mitochondrial dysfunction as a hallmark of brain senescence in telomerase-deficient mice

Mitophagy in neuronal health and disease: from mechanisms to neurodegeneration

Regulation of mitochondrial health is critical for maintaining cellular homeostasis in the nervous system. Damaged mitochondria can have detrimental effects on neuronal health and are thought to be key contributors to the progression of neurodegenerative disorders including Parkinson’s disease and amyotrophic lateral sclerosis. To mitigate this damage, multiple quality control mechanisms have evolved to eliminate aged or damaged mitochondria. One such quality control process is autophagy, a process that involves turnover of mitochondria at presynaptic sites and the axon terminal under basal conditions. This highly conserved mechanism sequesters mitochondria from the cytosol within autophagosomes followed by degradation upon fusion with a lysosome. Acute mitochondrial damage activates a selective form of autophagy called mitophagy that involves receptor-mediated engulfment and degradation of the damaged organelle. Multiple mechanisms have been shown to drive efficient mitophagy in neurons and glia, including PTEN induced kinase 1 (PINK1)/Parkin–dependent mitophagy and receptor-mediated mitophagy. Genetic, pathological, and experimental evidence all implicate defects in the removal of damaged mitochondria in the onset or progression of neurodegenerative disease. Both the initiation of PINK1/Parkin–dependent mitophagy and deficits in the removal of damaged mitochondria are linked to activation of neuroinflammatory pathways, including NF-κB and cyclic GMP-AMP synthase–stimulator of interferon genes (cGAS-STING) signaling. In this Review, we discuss the molecular pathways governing mitophagy in neurons and glial cells and how deficits in these pathways may lead to neurodegeneration. We also highlight emerging therapeutic strategies aimed at restoring mitophagy to preserve neuronal homeostasis and function.

Age-related disruptions in ubiquitination and mitochondrial proteostasis are associated with neuronal compartment-specific mitochondrial changes.

Declining aerodigestive neuromotor function is a major aspect of human aging, with impaired airway defense and swallow manoeuvres implicated in pneumonia and dysphagia. Hypoglossal motor neurons (MNs) innervate tongue muscles, essential for these behaviours. Their degeneration contributes to age-related aerodigestive dysfunctions. In neurodegenerative diseases, the ubiquitin-proteasome system (UPS) is altered, disturbing mitochondrial proteostasis. We have previously shown reduced mitochondrial abundance, dysfunction and mitochondrial fragmentation in aging hypoglossal MN somas and dendrites. However, the relationship between the UPS (pUBS65 and ubiquitinated proteins), mitochondrial fragmentation (pDRP1S616) and fusion promoting proteins (MFN2) in MN aging is unexplored. In other neurons, aging changes mitochondria within axons in an opposite way to somas and dendrites. We used Western blotting to show impairment in mitophagy-related pUBS65, increased fragmentation-promoting pDRP1S616 and unchanged MFN2. Serial Block-Face Scanning Electron Microscopy showed increased mitochondrial volume density and larger, more simplistic mitochondria in old, myelinated hypoglossal axons, while somas and dendrites showed reduced mitochondrial volume density and increased fragmentation. Our results suggest that a more nuanced compartment-specific evaluation of mitochondrial structure and function is required to fully elucidate the pathophysiology underlying age-related neuromotor dysfunction.

Role of ESCRT pathway and autophagy in neurodegenerative diseases.

This review synthesizes evidence from genetic, biochemical, and neuropathological studies to highlight shared molecular nodes, such as ESCRT-III components, the VPS4 ATPase, the adaptor protein ALIX, and late endosomal regulators, including Rab7 that couple membrane remodeling to autophagic flux.