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A-L, Extensive vacuolization of neuronal cell bodies. Semithin and ultrathin sections of DRGs (A-D), lumbar motoneurons (E-H ), and cerebellum (I-L ) of Afg3l2 par/par mice and controls at P14. Examples of multiple large intracytoplasmic vacuoles are indicated by empty polygons in the mutants (B, F, J). EM analysis shows giant mitochondria with swollen, disorganized cristae in the mutants (D, H, L, arrows) compared with controls (C, G, K ). Scale bars: (in A) A, B, E, F, I, J, 20 m; (in C) C, D, G, H, K, L, 1 m.
Source publication
The mitochondrial metalloprotease AFG3L2 assembles with the homologous protein paraplegin to form a supracomplex in charge of the essential protein quality control within mitochondria. Mutations of paraplegin cause a specific axonal degeneration of the upper motoneuron and, therefore, hereditary spastic paraplegia. Here we present two Afg3l2 murine...
Contexts in source publication
Context 1
... (neuron count per area of mu- tants vs control SD in anterior horn, DRGs, and Purkinje cells are, respectively, 7.75 1.29 vs 7.4 1; 20.2 1.86 vs 20 2.58; 9 1.67 vs 9 1.41). In fact, we find no evidence of neuronal loss, suggesting that this is not a primary event in these models. Multiple large vacuoles with clear content cluster in the cytoplasm (Fig. 3 B, F,J). As shown by EM examination, the observed vacuoles are suggestive of mito- chondrial origin (Fig. 3 D, H,L ). Displace- ment of the inner membrane, cristae dis- ruption and increased volume of the intermembrane space are observed in swollen ...
Context 2
... 7.75 1.29 vs 7.4 1; 20.2 1.86 vs 20 2.58; 9 1.67 vs 9 1.41). In fact, we find no evidence of neuronal loss, suggesting that this is not a primary event in these models. Multiple large vacuoles with clear content cluster in the cytoplasm (Fig. 3 B, F,J). As shown by EM examination, the observed vacuoles are suggestive of mito- chondrial origin (Fig. 3 D, H,L ). Displace- ment of the inner membrane, cristae dis- ruption and increased volume of the intermembrane space are observed in swollen ...
Citations
... For example, ACAD8 (upregulated), which is involved in fatty acid metabolism, can impact mitochondrial energy production 69 . AFG3L2 (downregulated), a gene associated with mitochondrial complex assembly, has implications in mitochondrial dysfunction and has been shown to be essential for axonal development 70 . Upregulation of the GLS gene, which catalyzes the conversion of glutamine to glutamate 71 , could be linked to altered glutamatergic signaling, potentially contributing to neuronal hyperexcitability 72 . ...
Parkinson’s disease (PD) is the second most prevalent neurodegenerative disease. Primary symptoms of PD arise with the loss of dopaminergic (DA) neurons in the Substantia Nigra Pars Compacta, but PD also affects the hippocampus and cortex, usually in its later stage. Approximately 15% of PD cases are familial with a genetic mutation. Two of the most associated genes with autosomal recessive (AR) early-onset familial PD are PINK1 and PRKN . In vitro studies of these genetic mutations are needed to understand the neurophysiological changes in patients’ neurons that may contribute to neurodegeneration. In this work, we generated and differentiated DA and hippocampal neurons from human induced pluripotent stem cells (hiPSCs) derived from two patients with a double mutation in their PINK1 and PRKN (one homozygous and one heterozygous) genes and assessed their neurophysiology compared to two healthy controls. We showed that the synaptic activity of PD neurons generated from patients with the PINK1 and PRKN mutations is impaired in the hippocampus and dopaminergic neurons. Mutant dopaminergic neurons had enhanced excitatory post-synaptic activity. In addition, DA neurons with the homozygous mutation of PINK1 exhibited more pronounced electrophysiological differences compared to the control neurons. Signaling network analysis of RNA sequencing results revealed that Focal adhesion and ECM receptor pathway were the top two upregulated pathways in the mutant PD neurons. Our findings reveal that the phenotypes linked to PINK1 and PRKN mutations differ from those from other PD mutations, suggesting a unique interplay between these two mutations that drives different PD mechanisms.
... Maltecca and co-workers have shown that Afg3l2 missense and null mutant mice have no effect on mitochondrial protein synthesis but impact on mitochondrial energy metabolism by impaired respiratory complex I and III activity due to inadequate assembling of these complexes. This is a result of swollen and giant mitochondria with damaged cristae generated in the vacuoles of Purkinje cells as well as cell bodies of the spinal cord and dorsal root ganglia that are located near to nucleus and cell membrane [56] affecting axonal transport (Fig. 3). They have further used carbonyl formation as a marker to emphasize the importance of oxidative stress in Afg3l2 mutants [57]. ...
... Early neuronal development in the demyelinated axons involves Nrg1-III signaling via ErbB receptors [59] while post-myelination axonic development involves phosphorylation of neurofilaments (NF) utilizing the kinase-phosphatase cycles [60]. Afg3l2 mutants impact the axon-glial cross talk because damaged axons affect myelination, result in insufficient NF phosphorylation and also cause glutamate excitotoxicity in glial cells [56,61]. ...
... However, all mutations discovered and documented so far are mostly in Caucasian populations. A novel G671R [c.2011G > C] mutation that was located in a highly conserved region of AFG3L2 gene in five patients of a Hungarian family showed similar characteristics to previously identified cases with no cognitive impairment [106] and [99] have identified two mutations-homozygous missense and homozygous null-that caused lethality in mice models due to impaired axon development in both CNS and PNS delayed myelination, and weak axonal radial growth [56]. In Spg7 deficient mice, Emv66 mutants of AFG3L2 show exacerbating axonopathy and severe neuromuscular defects in hetero-and homozygous conditions respectively with loss of PCs and parallel fibers [109]. ...
AFG3L2 is a zinc metalloprotease and an ATPase localized in an inner mitochondrial membrane involved in mitochondrial quality control of several nuclear- and mitochondrial-encoded proteins. Mutations in AFG3L2 lead to diseases like slow progressive ataxia, which is a neurological disorder. This review delineates the cellular functions of AFG3L2 and its dysfunction that leads to major clinical outcomes, which include spinocerebellar ataxia type 28, spastic ataxia type 5, and optic atrophy type 12. It summarizes all relevant AFG3L2 mutations associated with the clinical outcomes to understand the detailed mechanisms attributable to its structure-related multifaceted roles in proteostasis and quality control. We face early diagnostic challenges of ataxia and optic neuropathy due to asymptomatic parents and variable clinical manifestations due to heterozygosity/homozygosity of AFG3L2 mutations. This review intends to promote AFG3L2 as a putative prognostic or diagnostic marker.
Functions, mutations, and clinical manifestations in AFG3L2, a mitochondrial AAA + ATPases.
... To measure mitochondrial ATP production in cerebellum, we isolated fresh mitochondria and applied the same experimental procedure as described in (53) ...
Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS) is caused by mutations in SACS gene encoding sacsin, a huge protein highly expressed in cerebellar Purkinje cells (PCs). ARSACS patients, as well as mouse models, display early degeneration of PCs, but the underlying mechanisms remain unexplored, with no available treatments.In this work, we demonstrated aberrant calcium (Ca2+) homeostasis and its impact on PC degeneration in ARSACS. Mechanistically, we found pathological elevation in Ca2+-evoked responses in Sacs-/- PCs, as the result of defective mitochondria and ER trafficking to distal dendrites and strong downregulation of key Ca2+ buffer-proteins. Alteration of cytoskeletal linkers, that we identified as specific sacsin interactors, likely account for faulty organellar trafficking in Sacs-/- cerebellum.Based on this pathogenetic cascade, we treated Sacs-/- mice with Ceftriaxone, a repurposed drug which exerts neuroprotection by limiting neuronal glutamatergic stimulation, and thus Ca2+ fluxes into PCs. Ceftriaxone treatment significantly improved motor performances of Sacs-/- mice, at both pre- and post-symptomatic stages. We correlated this effect to restored Ca2+ homeostasis, which arrests PC degeneration and attenuates secondary neuroinflammation. These findings disclose new key steps in ARSACS pathogenesis and support further optimization of Ceftriaxone in pre-clinical and clinical settings for the treatment of ARSACSpatients.
... Mutant α-synuclein interacts with the TOM complex and disrupts import. It also recruits Drp1 to mitochondria, increasing fission, and suppresses mitochondrial protease activity Paraplegin Component of m-AAA protease Reduced paraplegin levels affect ribosomal processing and degradation of membrane proteins (Ferreirinha et al., 2004;Maltecca et al., 2008;Martinelli and Rugarli, 2010) Spinocerebellar ataxia AFG3L2 Component of m-AAA protease Reduced levels affect m-AAA enzyme activity, causing enlarged mitochondria, disrupted cristae, and impaired axonal trafficking (Martinelli and Rugarli, 2010;Smets et al., 2014) The protein huntingtin is not yet well-understood, but appears to shuttle between the nucleus and cytosol and interact with a large number of proteins, including transcription factors, and changes to these interactions may drive disease pathogenesis. The prevailing theory is mutations in huntingtin convey protein gain of function in HD; this leads to protein aggregation (Bossy-Wetzel et al., 2008;Tabrizi et al., 2020). ...
... Reduced complex I levels are also found in the brains of AFG3L2 knockout mice. Impaired axonal trafficking is also present in these cells, causing swelling and then degeneration (Maltecca et al., 2008). These changes can be reversed with rescue of paraplegin expression, as well as some degree of motor performance and neurological health (Pirozzi et al., 2014). ...
Increasing evidence implicates mitochondrial dysfunction as key in the development and progression of various forms of neurodegeneration. The multitude of functions carried out by mitochondria necessitates a tight regulation of protein import, dynamics, and turnover; this regulation is achieved via several, often overlapping pathways that function at different levels. The development of several major neurodegenerative diseases is associated with dysregulation of these pathways, and growing evidence suggests direct interactions between some pathogenic proteins and mitochondria. When these pathways are compromised, so is mitochondrial function, and the resulting deficits in bioenergetics, trafficking, and mitophagy can exacerbate pathogenic processes. In this review, we provide an overview of the regulatory mechanisms employed by mitochondria to maintain protein homeostasis and discuss the failure of these mechanisms in the context of several major proteinopathies.
... 23 Systemic knockout of mitochondrial proteases involved in MQC other than LONP1 (including CLPP, AFG3L2, and OMA1) does not cause embryonic lethality and allows embryos to develop normally. [34][35][36] SMART RNA-seq analysis of oocytes after LONP1 ablation revealed that the expression of a large number of genes, especially mtUPR-and ribosome-related genes, was significantly upregulated in MII oocytes. Recent research has also shown that LONP1 is associated with RNA degradation and mitochondrial gene transcription. ...
Background
Oogenesis is a fundamental process of human reproduction, and mitochondria play crucial roles in oocyte competence. Mitochondrial ATP-dependent Lon protease 1 (LONP1) functions as a critical protein in maintaining mitochondrial and cellular homeostasis in somatic cells. However, the essential role of LONP1 in maintaining mammalian oogenesis is far from elucidated.
Methods
Using conditional oocyte Lonp1-knockout mice, RNA sequencing (RNA-seq) and coimmunoprecipitation/liquid chromatography–mass spectrometry (Co-IP/LC–MS) technology, we analysed the functions of LONP1 in mammalian oogenesis.
Findings
Conditional knockout of Lonp1 in mouse oocytes in both the primordial and growing follicle stages impairs follicular development and causes progressive oocyte death, ovarian reserve loss, and infertility. LONP1 directly interacts with apoptosis inducing factor mitochondria-associated 1 (AIFM1), and LONP1 ablation leads to the translocation of AIFM1 from the cytoplasm to the nucleus, causing apoptosis in mouse oocytes. In addition, women with pathogenic variants of LONP1 lack large antral follicles (>10 mm) in the ovaries, are infertile and present premature ovarian insufficiency.
Interpretation
We demonstrated the function of LONP1 in regulating oocyte development and survival, and in-depth analysis of LONP1 will be crucial for elucidating the mechanisms underlying premature ovarian insufficiency.
Funding
This work was supported by grants from the National Key Research and Development Program of China (2018YFC1004701), the National Nature Science Foundation of China (82001629, 81871128, 81571391, 81401166, 82030040), the Jiangsu Province Social Development Project (BE2018602), the Jiangsu Provincial Medical Youth Talent (QNRC2016006), the Youth Program of the Natural Science Foundation of Jiangsu Province (BK20200116) and Jiangsu Province Postdoctoral Research Funding (2021K277B).
... Most commonly, mice with loss of autosomal OA-causing genes display: reduced body size and difficulty gaining weight (Smith et al., 2012;Wells et al., 2012) and cardiomyopathy (Davies et al., 2008;Jiang et al., 2021). In many cases, these symptoms are not detectable in patients carrying the comparable pathogenic mutation and whilst many autosomal OA-causing genes are thought to have a developmental role in humans, there is presently little evidence for developmental abnormalities affecting these organs in patients (Maltecca et al., 2008;Caglayan et al., 2020). ...
... Opa3 (Davies et al., 2008), Afg3l2 (Maltecca et al., 2008), are 2 principal methods of genetic manipulation in zebrafish embryos, CRISPR/Cas9 and morpholinos. Morpholinos are short oligomers designed to be complementary to the transcription start site or splice site of pre-mRNAs to transiently block splicing or translation of a desired transcript, reducing the expression of the target gene. ...
Optic atrophy (OA) with autosomal inheritance is a form of optic neuropathy characterized by the progressive and irreversible loss of vision. In some cases, this is accompanied by additional, typically neurological, extra-ocular symptoms. Underlying the loss of vision is the specific degeneration of the retinal ganglion cells (RGCs) which form the optic nerve. Whilst autosomal OA is genetically heterogenous, all currently identified causative genes appear to be associated with mitochondrial organization and function. However, it is unclear why RGCs are particularly vulnerable to mitochondrial aberration. Despite the relatively high prevalence of this disorder, there are currently no approved treatments. Combined with the lack of knowledge concerning the mechanisms through which aberrant mitochondrial function leads to RGC death, there remains a clear need for further research to identify the underlying mechanisms and develop treatments for this condition. This review summarizes the genes known to be causative of autosomal OA and the mitochondrial dysfunction caused by pathogenic mutations. Furthermore, we discuss the suitability of available in vivo models for autosomal OA with regards to both treatment development and furthering the understanding of autosomal OA pathology.
... Other studies have shown that proteases involved in mitochondrial quality control, including CLPP, AFG3L2, PHB, OMA1, LONP1, and PARL, also play crucial roles in ovarian cells, as deficiencies in these proteases lead to the onset of mitochondrial-related diseases and accelerate oocyte aging [33][34][35]. Multidrug resistance transporter-1 (MDR-1) is known for its pathological role in tumor escape during chemotherapy. Mutations in MDR-1 can destroy the homeostasis of mitochondria in oocytes and ovaries. ...
The female reproductive system is of great significance to women's health. Aging of the female reproductive system occurs approximately 10 years prior to the natural age-associated functional decline of other organ systems. With an increase in life expectancy worldwide, reproductive aging has gradually become a key health issue among women. Therefore, an adequate understanding of the causes and molecular mechanisms of ovarian aging is essential towards the inhibition of age-related diseases and the promotion of health and longevity in women. In general, women begin to experience a decline in ovarian function around the age of 35 years, which is mainly manifested as a decrease in the number of ovarian follicles and the quality of oocytes. Studies have revealed the occurrence of mitochondrial dysfunction, reduced DNA repair, epigenetic changes, and metabolic alterations in the cells within the ovaries as age increases. In the present work, we reviewed the possible factors of aging-induced ovarian insufficiency based on its clinical diagnosis and performed an in-depth investigation of the relevant molecular mechanisms and potential targets to provide novel approaches for the effective improvement of ovarian function in older women.
... Through selective degradation of non-assembled and damaged proteins, the m-AAA complex exerts protein quality control surveillance in the inner membrane [7], while through its chaperone-like activity participates in the assembly of respiratory chain complexes [8][9][10]. Furthermore, the m-AAA complex mediates the proteolytic activation of substrates such as the nuclear-encoded subunit of mitochondrial ribosome MrpL32, the regulator of mitochondrial fusion protein OPA1 [11] , [12]. ...
... Dominant mutations of AFG3L2, the paraplegin partner in the m-AAA complex, are responsible for spinocerebellar ataxia type 28 (SCA28) [13]. Extensive investigation of AFG3L2 association with SCA28 pathogenesis points to a role in the control of organelle fragmentation and Ca 2+ buffering in Purkinje neurons [10] , [14][15][16][17]. A third very rare and severe disease, SPAX5, has been associated with recessive mutations of AFG3L2 and recalls features of both SCA28 and SPG7 [18]. ...
Background
Mutations of the mitochondrial protein paraplegin cause hereditary spastic paraplegia type 7 (SPG7), a so-far untreatable degenerative disease of the upper motoneuron with still undefined pathomechanism.
The intermittent mitochondrial permeability transition pore (mPTP) opening, called flickering, is an essential process that operates to maintain mitochondrial homeostasis by reducing intra-matrix Ca2+ and reactive oxygen species (ROS) concentration, and is critical for efficient synaptic function.
Methods
We use a fluorescence-based approach to measure mPTP flickering in living cells and biochemical and molecular biology techniques to dissect the pathogenic mechanism of SPG7. In the SPG7 animal model we evaluate the potential improvement of the motor defect, neuroinflammation and neurodegeneration by means of an mPTP inducer, the benzodiazepine Bz-423.
Findings
We demonstrate that paraplegin is required for efficient transient opening of the mPTP, that is impaired in both SPG7 patients-derived fibroblasts and primary neurons from Spg7−/− mice. We show that dysregulation of mPTP opening at the pre-synaptic terminal impairs neurotransmitter release leading to ineffective synaptic transmission. Lack of paraplegin impairs mPTP flickering by a mechanism involving increased expression and activity of sirtuin3, which promotes deacetylation of cyclophilin D, thus hampering mPTP opening. Pharmacological treatment with Bz-423, which bypasses the activity of CypD, normalizes synaptic transmission and rescues the motor impairment of the SPG7 mouse model.
Interpretation
mPTP targeting opens a new avenue for the potential therapy of this form of spastic paraplegia.
... The genes we identified appear to be associated with four general functions that make sense in the context of switching phenotypes in response to the environment. First, three genes (GPR83, CLIP1, andAFG3L2) are associated with learning, behavior, and/or neuron development (Almajan et al., 2012;Gomes et al., 2016;Larti et al., 2015;Maltecca et al., 2008). Such cognition-related functions could be related to assessing the dynamic state of the environment and making foraging and developmental decisions depending on the environment. ...
Phenotypic plasticity allows organisms to alter their phenotype in direct response to changes in the environment. Despite growing recognition of plasticity's role in ecology and evolution, few studies have probed plasticity's molecular bases—especially using natural populations. We investigated the genetic basis of phenotypic plasticity in natural populations of spadefoot toads (Spea multiplicata ). Spea tadpoles normally develop into an “omnivore” morph that is favored in long‐lasting, low‐density ponds. However, if tadpoles consume freshwater shrimp or other tadpoles, they can alternatively develop (via plasticity) into a “carnivore” morph that is favored in ephemeral, high‐density ponds. By combining natural variation in pond ecology and morph production with population genetic approaches, we identified candidate loci associated with each morph (carnivores vs. omnivores) and loci associated with adaptive phenotypic plasticity (adaptive vs. maladaptive morph choice). Our candidate morph loci mapped to two genes, whereas our candidate plasticity loci mapped to 14 genes. In both cases, the identified genes tended to have functions related to their putative role in spadefoot tadpole biology. Our results thereby form the basis for future studies into the molecular mechanisms that mediate plasticity in spadefoots. More generally, these results illustrate how diverse loci might mediate adaptive plasticity.
... However, it remains to be determined if these demyelinating neurological symptoms could be directly related to the AFG3L2 mutation. Although mouse studies have shown that deletion of AFG3L2 (either constitutive or in mature mouse oligodendrocytes) can cause myelin abnormalities [17,18], no such phenotype has been described in humans before. Comorbidity cannot therefore be excluded in the proband. ...
Autosomal dominant optic atrophy (ADOA) is a neuro-ophthalmic condition characterized by bilateral degeneration of the optic nerves. Although heterozygous mutations in OPA1 represent the most common genetic cause of ADOA, a significant number of cases remain undiagnosed.
Here, we describe a family with a strong ADOA history with most family members spanning three generation having childhood onset of visual symptoms. The proband, in addition to optic atrophy, had neurological symptoms consistent with relapsing remitting multiple sclerosis. Clinical exome analysis detected a novel mutation in the AFG3L2 gene (NM_006796.2:c.1010G > A; p.G337E), which segregated with optic atrophy in family members. AFG3L2 is a metalloprotease of the AAA subfamily which exerts quality control in the inner mitochondrial membrane. Interestingly, the identified mutation localizes close to the AAA domain of AFG3L2, while those localized in the proteolytic domain cause dominant spinocerebellar ataxia type 28 (SCA28) or recessive spastic ataxia with epilepsy (SPAX5). Functional studies in patient fibroblasts demonstrate that the p.G337E AFG3L2 mutation strongly destabilizes the long isoforms of OPA1 via OMA hyper-activation and leads to mitochondrial fragmentation, thus explaining the family phenotype. This study widens the clinical spectrum of neurodegenerative diseases caused by AFG3L2 mutations, which shall be considered as genetic cause of ADOA.
