Abstract:A healthy mitochondrial network is essential for the maintenance of neuronal synaptic integrity. Mitochondrial and metabolic dysfunction contributes to the pathogenesis of many neurodegenerative diseases including dementia. OPA1 is the master regulator of mitochondrial fusion and fission and is likely to play an important role during neurodegenerative events. To explore this, we quantified hippocampal dendritic and synaptic integrity and the learning and memory performance of aged Opa1 haploinsufficient mice c… Show more
“…Opa1 K301A -expressing nematodes display fewer SNB-1::GFP puncta and larger synaptic regions in GABAergic motor neurons (Fig. 5e–g ), a finding consistent with the observed reduction in synapses in mammalian cortical neurons where Opa1 was ablated [ 30 ] and in RGCs and hippocampal neurons of an ADOA mouse model [ 44 , 45 ]. Fig.…”
Mitochondrial dysfunction and mitophagy are often hallmarks of neurodegenerative diseases such as autosomal dominant optic atrophy (ADOA) caused by mutations in the key mitochondrial dynamics protein optic atrophy 1 (Opa1). However, the second messengers linking mitochondrial dysfunction to initiation of mitophagy remain poorly characterized. Here, we show in mammalian and nematode neurons that Opa1 mutations trigger Ca2+-dependent mitophagy. Deletion or expression of mutated Opa1 in mouse retinal ganglion cells and Caenorhabditis elegans motor neurons lead to mitochondrial dysfunction, increased cytosolic Ca2+ levels, and decreased axonal mitochondrial density. Chelation of Ca2+ restores mitochondrial density in neuronal processes, neuronal function, and viability. Mechanistically, sustained Ca2+ levels activate calcineurin and AMPK, placed in the same genetic pathway regulating axonal mitochondrial density. Our data reveal that mitophagy in ADOA depends on Ca2+-calcineurin-AMPK signaling cascade.
“…Opa1 K301A -expressing nematodes display fewer SNB-1::GFP puncta and larger synaptic regions in GABAergic motor neurons (Fig. 5e–g ), a finding consistent with the observed reduction in synapses in mammalian cortical neurons where Opa1 was ablated [ 30 ] and in RGCs and hippocampal neurons of an ADOA mouse model [ 44 , 45 ]. Fig.…”
Mitochondrial dysfunction and mitophagy are often hallmarks of neurodegenerative diseases such as autosomal dominant optic atrophy (ADOA) caused by mutations in the key mitochondrial dynamics protein optic atrophy 1 (Opa1). However, the second messengers linking mitochondrial dysfunction to initiation of mitophagy remain poorly characterized. Here, we show in mammalian and nematode neurons that Opa1 mutations trigger Ca2+-dependent mitophagy. Deletion or expression of mutated Opa1 in mouse retinal ganglion cells and Caenorhabditis elegans motor neurons lead to mitochondrial dysfunction, increased cytosolic Ca2+ levels, and decreased axonal mitochondrial density. Chelation of Ca2+ restores mitochondrial density in neuronal processes, neuronal function, and viability. Mechanistically, sustained Ca2+ levels activate calcineurin and AMPK, placed in the same genetic pathway regulating axonal mitochondrial density. Our data reveal that mitophagy in ADOA depends on Ca2+-calcineurin-AMPK signaling cascade.
“…In agreement, these animals, like most DOA patients, display late-onset visual deficits due to optic nerve degeneration (Lenaers et al, 2021). Using another DOA mouse model, a recent study reported cognitive impairments at older age (over 14 months), when visual impairments are described, precluding reliable determination of the cognitive profile of these mice at this age (Bevan et al, 2020).…”
Mitochondria are integrative hubs central to cellular adaptive pathways. Such pathways are critical in highly differentiated post-mitotic neurons, the plasticity of which sustains brain function. Consequently, defects in mitochondrial dynamics and quality control appear instrumental in neurodegenerative diseases and may also participate in cognitive impairments. To directly test this hypothesis, we analyzed cognitive performances in a mouse mitochondria-based disease model, due to haploinsufficiency in the mitochondrial optic-atrophy-type-1 (OPA1) protein. While in Dominant Optic Atrophy (DOA) models, the known main symptoms are late onset visual deficits, we discovered early impairments in hippocampus-dependent spatial memory attributable to defects in adult neurogenesis. Moreover, less connected hippocampal adult-born neurons showed a decrease in mitochondrial content. Remarkably, modulating mitochondrial function through voluntary exercise or pharmacological treatment restored spatial memory.Altogether, our study identifies a crucial role for OPA1-dependent mitochondrial functions in adult neurogenesis, and thus in hippocampal-dependent cognitive functions. More generally, our findings show that adult neurogenesis is highly sensitive to mild mitochondrial defects, generating impairments in spatial memory that can be detected at an early stage and counterbalanced by physical exercise and pharmacological targeting of mitochondrial dynamics. Thus, early amplification of mitochondrial function appears beneficial for late-onset neurodegenerative diseases.
“…CA1 neurons of Opa1 +/− mice display reduced spine density. Interestingly, Opa1 +/− CA1 neurons of female mice have significantly shorter dendrites and lower ATP production compared with male mice, which together contribute to a distinct form of memory loss [148,149]. The lack of Opa1 has been demonstrated to induce mitochondrial respiratory defects and mitochondrial fragmentation, as well as a reduction in mitochondrial density of neuronal axons in Drosophila larvae.…”
Section: Mitochondrial Fusion and Fission In The Nervous Systemmentioning
Biological sex influences disease development and progression. The steroid hormone 17β-oestradiol (E2), along with its receptors, is expected to play a major role in the manifestation of sex differences. E2 exerts pleiotropic effects in a system-specific manner. Mitochondria are one of the central targets of E2, and their biogenesis and respiration are known to be modulated by E2. More recently, it has become apparent that E2 also regulates mitochondrial fusion–fission dynamics, thereby affecting cellular metabolism. The aim of this article is to discuss the regulatory pathways by which E2 orchestrates the activity of several components of mitochondrial dynamics in the cardiovascular and nervous systems in health and disease. We conclude that E2 regulates mitochondrial dynamics to maintain the mitochondrial network promoting mitochondrial fusion and attenuating mitochondrial fission in both the cardiovascular and nervous systems.
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