Proteolytic Cleavage of Opa1 Stimulates Mitochondrial Inner Membrane Fusion and Couples Fusion to Oxidative Phosphorylation

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Mitochondrial DNA Mutations and Pathogenesis

Approximately three years ago, this journal published a review on the clinical and molecular analysis of mitochondrial encephalomyopathies, with emphasis on defects in mitochondrial DNA (mtDNA). At that time, approximately 30 point mutations associated with a variety of maternally-inherited (or rarely, sporadic) disorders had been described. Since that time, almost twenty new pathogenic mtDNA point mutations have been described, and the pace of discovery of such mutations shows no signs of abating. This accumulating body of data has begun to reveal some patterns that may be relevant to pathogenesis.     

Mutations in the Voltage-Dependent Anion Channel of the Mitochondrial Outer Membrane Cause a Dominant Nonlethal Growth Impairment

Point mutations at K234 and K236 in the yeast voltage-dependent anionchannel 1 (VDAC1) of the mitochondrial outer membrane have been shown tomarkedly impair the membrane insertion of this protein (Smith etal., 1995; Angeles et al., 1998). Mutants of this type wereexpressed in vivo in a strain of yeast with a disruption in theVDAC1 gene. Expression of the various VDAC1 forms was under the control of aGal1 promoter. Wild-type VDAC1 expression fully complemented the slow growthphenotype caused by the disruption. VDAC1 mutants in which K234 and K236 werereplaced by arginine, glutamate, or glutamine caused a more severe negativeeffect on growth. This effect appeared to be dominant since the mutant VDAC1forms suppressed growth in a yeast strain that retained its VDAC1 gene. Thisapparent dominant negative effect on growth did not seem to be specific forany stage of the cell cycle. However, the growth defect was not lethal as theaffected cells still could accumulate the vital stain, FUN1. Expression of amutant in which K234 had been replaced by glutamate had more serious negativegrowth effects than did a similar mutation at K236. Expression of71-116 VDAC1 complemented the VDAC1 disruption; however, expression ofthe same deletion mutant in which the lysines corresponding to K234 and K236were mutated to glutamate severely impaired growth. These results have shownthat a deficiency of lysine at positions 234 and 236 in VDAC1 causes anonlethal growth defect that is more severe than deletion of 45 amino acidsfrom VDAC1 or disruption of the VDAC1 gene. They also indicate that there is ahierarchy in the importance of these lysines with mutations at K234 being themore serious.     

Mutations Affecting a Yeast Mitochondrial Inner Membrane Protein, Pnt1p, Block Export of a Mitochondrially Synthesized Fusion Protein from the Matrix

The machinery that inserts mitochondrially encoded proteins into the inner membrane and translocates their hydrophilic domains through the membrane is poorly understood. We have developed a genetic screen for Saccharomyces cerevisiae mutants defective in this export process. The screen is based on the fact that the hydrophilic polypeptide Arg8(m)p is exported from the matrix if it is synthesized within mitochondria as a bifunctional Cox2p-Arg8(m)p fusion protein. Since export of Arg8(m)p causes an Arg(-) phenotype, defective mutants can be selected as Arg(+). Here we show that mutations in the nuclear gene PNT1 block the translocation of mitochondrially encoded fusion proteins across the inner membrane. Pnt1p is a mitochondrial integral inner membrane protein that appears to have two hydrophilic domains in the matrix, flanking a central hydrophobic hairpin-like anchor. While an S. cerevisiae pnt1 deletion mutant was more sensitive to H(2)O(2) than the wild type was, it was respiration competent and able to export wild-type Cox2p. However, deletion of the PNT1 orthologue from Kluyveromyces lactis, KlPNT1, caused a clear nonrespiratory phenotype, absence of cytochrome oxidase activity, and a defect in the assembly of KlCox2p that appears to be due to a block of C-tail export. Since PNT1 was previously described as a gene affecting resistance to the antibiotic pentamidine, our data support a mitochondrial target for this drug.     

Length Mutations in Human Mitochondrial DNA

By high-resolution, restriction mapping of mitochondrial DNAs purified from 112 human individuals, we have identified 14 length variants caused by small additions and deletions (from about 6 to 14 base pairs in length). Three of the 14 length differences are due to mutations at two locations within the D loop, whereas the remaining 11 occur at seven sites that are probably within other noncoding sequences and at junctions between coding sequences. In five of the nine regions of length polymorphism, there is a sequence of five cytosines in a row, this sequence being comparatively rare in coding DNA. Phylogenetic analysis indicates that, in most of the polymorphic regions, a given length mutation has arisen several times independently in different human lineages. The average rate at which length mutations have been arising and surviving in the human species is estimated to be many times higher for noncoding mtDNA than for noncoding nuclear DNA. The mystery of why vertebrate mtDNA is more prone than nuclear DNA to evolve by point mutation is now compounded by the discovery of a similar bias toward rapid evolution by length mutation.     

Recurrent De Novo Dominant Mutations in SLC25A4 Cause Severe Early-Onset Mitochondrial Disease and Loss of Mitochondrial DNA Copy Number

Mutations in SLC25A4 encoding the mitochondrial ADP/ATP carrier AAC1 are well-recognized causes of mitochondrial disease. Several heterozygous SLC25A4 mutations cause adult-onset autosomal-dominant progressive external ophthalmoplegia associated with multiple mitochondrial DNA deletions, whereas recessive SLC25A4 mutations cause childhood-onset mitochondrial myopathy and cardiomyopathy. Here, we describe the identification by whole-exome sequencing of seven probands harboring dominant, de novo SLC25A4 mutations. All affected individuals presented at birth, were ventilator dependent and, where tested, revealed severe combined mitochondrial respiratory chain deficiencies associated with a marked loss of mitochondrial DNA copy number in skeletal muscle. Strikingly, an identical c.239G>A (p.Arg80His) mutation was present in four of the seven subjects, and the other three case subjects harbored the same c.703C>G (p.Arg235Gly) mutation. Analysis of skeletal muscle revealed a marked decrease of AAC1 protein levels and loss of respiratory chain complexes containing mitochondrial DNA-encoded subunits. We show that both recombinant AAC1 mutant proteins are severely impaired in ADP/ATP transport, affecting most likely the substrate binding and mechanics of the carrier, respectively. This highly reduced capacity for transport probably affects mitochondrial DNA maintenance and in turn respiration, causing a severe energy crisis. The confirmation of the pathogenicity of these de novo SLC25A4 mutations highlights a third distinct clinical phenotype associated with mutation of this gene and demonstrates that early-onset mitochondrial disease can be caused by recurrent de novo mutations, which has significant implications for the application and analysis of whole-exome sequencing data in mitochondrial disease.     

Suppression of Mitochondrial DNA Instability of Autosomal Dominant Forms of Progressive External Ophthalmoplegia-Associated ANT1 Mutations in Podospora anserina

Maintenance and expression of mitochondrial DNA (mtDNA) are essential for the cell and the organism. In humans, several mutations in the adenine nucleotide translocase gene ANT1 are associated with multiple mtDNA deletions and autosomal dominant forms of progressive external ophthalmoplegia (adPEO). The mechanisms underlying the mtDNA instability are still obscure. A current hypothesis proposes that these pathogenic mutations primarily uncouple the mitochondrial inner membrane, which secondarily causes mtDNA instability. Here we show that the three adPEO-associated mutations equivalent to A114P, L98P, and V289M introduced into the Podospora anserina ANT1 ortholog dominantly cause severe growth defects, decreased reactive oxygen species production (ROS), decreased mitochondrial inner membrane potential (Δψ), and accumulation of large-scale mtDNA deletions leading to premature death. Interestingly, we show that, at least for the adPEO-type M106P and A121P mutant alleles, the associated mtDNA instability cannot be attributed only to a reduced membrane potential or to an increased ROS level since it can be suppressed without restoration of the Δψ or modification of the ROS production. Suppression of mtDNA instability due to the M106P and A121P mutations was obtained by an allele of the rmp1 gene involved in nucleo-mitochondrial cross- talk and also by an allele of the AS1 gene encoding a cytosolic ribosomal protein. In contrast, the mtDNA instability caused by the S296M mutation was not suppressed by these alleles.THE maintenance and expression of mitochondrial DNA (mtDNA) depend on many nuclear-encoded gene products. Recent studies have shown that defects in this maintenance can have devastating consequences for the cell and the organism. In humans, these defects are an important cause of neurological diseases including autosomal dominant (or recessive) progressive external ophthalmoplegia (adPEO) (Chinnery 2003; Copeland 2008). These disorders are characterized by multiple large-scale deletions of mtDNA. Three different genes that can cause PEO with multiple mtDNA deletions have been identified: the mtDNA polymerase (POLG), the heart/muscle isoform of the adenine nucleotide translocator (ANT1), and the mitochondrial DNA helicase, Twinkle.The adenine nucleotide translocator (ANT), also known as the ADP/ATP mitochondrial translocator, is the most abundant protein in the inner mitochondrial membrane (Riccio et al. 1975; Nury et al. 2006; Klingenberg 2008). It exports ATP produced by mitochondrial oxidative phosphorylation toward the cytosol to meet the energy requirements of the cell; in exchange, it transports ADP into the mitochondrial matrix to fuel the conversion of ADP to ATP by the F₁F_O-ATP synthase. In humans, four isoforms of the ANT protein exist, and they are differently expressed in a tissue-specific manner (Stepien et al. 1992; Palmieri 2004; Dolce et al. 2005). The human ANT1 isoform is predominantly expressed in skeletal and cardiac muscle, and specific ANT1 mutations are associated with adPEO characterized by mtDNA instability (Kaukonen et al. 1999, 2000; Napoli et al. 2001; Komaki et al. 2002; Siciliano et al. 2003). In mice, Ant1 knockout induces mitochondrial myopathy (Graham et al. 1997), increased H₂O₂ production, and mtDNA damage and inhibits oxidative phosphorylation (Esposito et al. 1999). Some of these mutations were introduced in the AAC2 gene of Saccharomyces cerevisiae that encodes the major ADP/ATP mitochondrial translocator isoform in this organism. Numerous and sometimes contradictory effects have been reported depending in particular on the yeast laboratory strains examined (Kaukonen et al. 2000; Chen 2002, 2004; Fontanesi et al. 2004; Palmieri et al. 2005; Wang et al. 2008b).In an attempt to better understand how these mutations affect mitochondrial DNA stability and their functional consequences on mitochondrial metabolism, we decided to introduce them in the unique ADP/ATP translocator gene of Podospora anserina, PaAnt. Like S. cerevisiae, the filamentous fungus P. anserina is an excellent system for genetic and molecular analyses. In contrast to S. cerevisiae, it is a strict multicellular aerobe that can display heteroplasmic states in which intact and rearranged mitochondrial genomes coexist. In this organism, life span is a reflection of mtDNA stability, and death is always associated with large mtDNA rearrangements. “Natural death” or aging is accompanied by large-scale reorganizations of the mtDNA whereas a nuclear-controlled premature death syndrome is accompanied by the accumulation of site-specific mtDNA deletions (Belcour et al. 1999; Silar et al. 2001 for reviews). P. anserina therefore occupies an interesting position among model systems for studying the cellular consequences of mutations in the ADP/ATP translocase gene.We show here that the mutations M106P, A121P, and S296M, equivalent to the L98P, A114P (familial), and V289M (sporadic) human mutations, severely impair the vegetative and sexual development of the fungus and are responsible for decreased ROS production and for decreased inner membrane potential (Δψ). The severity of the phenotypes differs according to the mutation. The three mutations show mtDNA instability, which leads to premature death. All these mutated traits are dominant. Interestingly, the mtDNA instability associated with the M106P and A121P mutations depends on the rmp1 gene. This gene exists under two naturally occurring alleles, rmp1-1 and rmp1-2, which control mtDNA integrity in some genetic contexts (Belcour et al. 1991; Contamine et al. 1996, 2004). When associated with the rmp1-1 allele, the M106P and A121P mutations lead to rapid mtDNA instability whereas, in the presence of the rmp1-2 allele, mtDNA instability is suppressed, and life span is considerably increased. Surprisingly, suppression is not accompanied by a restoration of the Δψ or a modification in the ROS level, demonstrating that these parameters are not sufficient to explain the M106P and A121P mtDNA instability. Mitochondrial DNA instability due to the M106P and A121P mutations is also suppressed by a mutation in the AS1 gene encoding a ribosomal protein. The suppressor effects are not observed for the S296M mutation.     

Mitochondrial DNA Mutations Induce Mitochondrial Dysfunction,Apoptosis and Sarcopenia in Skeletal Muscle of Mitochondrial DNA Mutator Mice

Background

Aging results in a progressive loss of skeletal muscle, a condition known as sarcopenia. Mitochondrial DNA (mtDNA) mutations accumulate with aging in skeletal muscle and correlate with muscle loss, although no causal relationship has been established.

Methodology/Principal Findings

We investigated the relationship between mtDNA mutations and sarcopenia at the gene expression and biochemical levels using a mouse model that expresses a proofreading-deficient version (D257A) of the mitochondrial DNA Polymerase γ, resulting in increased spontaneous mtDNA mutation rates. Gene expression profiling of D257A mice followed by Parametric Analysis of Gene Set Enrichment (PAGE) indicates that the D257A mutation is associated with a profound downregulation of gene sets associated with mitochondrial function. At the biochemical level, sarcopenia in D257A mice is associated with a marked reduction (35–50%) in the content of electron transport chain (ETC) complexes I, III and IV, all of which are partly encoded by mtDNA. D257A mice display impaired mitochondrial bioenergetics associated with compromised state-3 respiration, lower ATP content and a resulting decrease in mitochondrial membrane potential (Δψ_m). Surprisingly, mitochondrial dysfunction was not accompanied by an increase in mitochondrial reactive oxygen species (ROS) production or oxidative damage.

Conclusions/Significance

These findings demonstrate that mutations in mtDNA can be causal in sarcopenia by affecting the assembly of functional ETC complexes, the lack of which provokes a decrease in oxidative phosphorylation, without an increase in oxidative stress, and ultimately, skeletal muscle apoptosis and sarcopenia.     

Prohibitin 2 Is an Inner Mitochondrial Membrane Mitophagy Receptor

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脂质膜体与线粒体内膜的融合

<正> 膜融合现象在细胞免疫、细胞识别和相互作用、病毒感架、细胞分泌以及细胞器之间相互关系等方面均有重要意义。利用人工脂质膜体(liposome)与细胞(器)膜之间的融合,不但为阐明上述问题的分子机理提供了一种模型,而且将为细胞生物工程研究提供手段。本文是我们实验室关于脂质膜体与鼠肝线粒体内膜体(mitoplast)融合的一系列研究结果的简要报道。     

The Role of Mitochondrial DNA Mutations in Hearing Loss

Mutations in mitochondrial DNA (mtDNA) are one of the most important causes of hearing loss. Of these, the homoplasmic A1555G and C1494T mutations at the highly conserved decoding site of the 12S rRNA gene are well documented as being associated with either aminoglycoside-induced or nonsyndromic hearing loss in many families worldwide. Moreover, five mutations associated with nonsyndromic hearing loss have been identified in the tRNA^Ser(UCN) gene: A7445G, 7472insC, T7505C, T7510C, and T7511C. Other mtDNA mutations associated with deafness are mainly located in tRNA and protein-coding genes. Failures in mitochondrial tRNA metabolism or protein synthesis were observed from cybrid cells harboring these primary mutations, thereby causing the mitochondrial dysfunctions responsible for deafness. This review article provides a detailed summary of mtDNA mutations that have been reported in deafness and further discusses the molecular mechanisms of these mtDNA mutations in deafness expression.     

Mitochondrial Fragmentation Due to Inhibition of Fusion Increases Cyclin B through Mitochondrial Superoxide Radicals

During the cell cycle, mitochondria undergo regulated changes in morphology. Two particularly interesting events are first, mitochondrial hyperfusion during the G₁-S transition and second, fragmentation during entry into mitosis. The mitochondria remain fragmented between late G₂- and mitotic exit. This mitotic mitochondrial fragmentation constitutes a checkpoint in some cell types, of which little is known. We bypass the ‘mitotic mitochondrial fragmentation’ checkpoint by inducing fragmented mitochondrial morphology and then measure the effect on cell cycle progression. Using Drosophila larval hemocytes, Drosophila S2R⁺ cell and cells in the pouch region of wing imaginal disc of Drosophila larvae we show that inhibiting mitochondrial fusion, thereby increasing fragmentation, causes cellular hyperproliferation and an increase in mitotic index. However, mitochondrial fragmentation due to over-expression of the mitochondrial fission machinery does not cause these changes. Our experiments suggest that the inhibition of mitochondrial fusion increases superoxide radical content and leads to the upregulation of cyclin B that culminates in the observed changes in the cell cycle. We provide evidence for the importance of mitochondrial superoxide in this process. Our results provide an insight into the need for mitofusin-degradation during mitosis and also help in understanding the mechanism by which mitofusins may function as tumor suppressors.     

Mimivirus-Encoded Nucleotide Translocator VMC1 Targets the Mitochondrial Inner Membrane

Mimivirus (Acanthamoeba polyphaga mimivirus) was the first giant DNA virus identified in an amoeba species. Its genome contains at least 979 genes. One of these, L276, encodes a nucleotide translocator with similarities to mitochondrial metabolite carriers, provisionally named viral mitochondrial carrier 1 (VMC1). In this study, we investigated the intracellular distribution of VMC1 upon expression in HeLa cells and in the yeast Saccharomyces cerevisiae. We found that VMC1 is specifically targeted to mitochondria and to the inner mitochondrial membrane. Newly synthesized VMC1 binds to the mitochondrial outer-membrane protein Tom70 and translocates through the import channel formed by the β-barrel protein Tom40. Derivatization of the four cysteine residues inside Tom40 by N-ethylmaleimide caused a delay in translocation but not a complete occlusion. Cell viability was not reduced by VMC1. Neither the mitochondrial membrane potential nor the intracellular production of reactive oxygen species was affected. Similar to endogenous metabolite carriers, mimivirus-encoded VMC1 appears to act as a specific translocator in the mitochondrial inner membrane. Due to its permeability for deoxyribonucleotides, VMC1 confers to the mitochondria an opportunity to contribute nucleotides for the replication of the large DNA genome of the virus.     

Disease Mutations in the Human Mitochondrial DNA Polymerase Thumb Subdomain Impart Severe Defects in Mitochondrial DNA Replication

Forty-five different point mutations in POLG, the gene encoding the catalytic subunit of the human mitochondrial DNA polymerase (pol γ), cause the early onset mitochondrial DNA depletion disorder, Alpers syndrome. Sequence analysis of the C-terminal polymerase region of pol γ revealed a cluster of four Alpers mutations at highly conserved residues in the thumb subdomain (G848S, c.2542g→a; T851A, c.2551a→g; R852C, c.2554c→t; R853Q, c.2558g→a) and two Alpers mutations at less conserved positions in the adjacent palm subdomain (Q879H, c.2637g→t and T885S, c.2653a→t). Biochemical characterization of purified, recombinant forms of pol γ revealed that Alpers mutations in the thumb subdomain reduced polymerase activity more than 99% relative to the wild-type enzyme, whereas the palm subdomain mutations retained 50–70% wild-type polymerase activity. All six mutant enzymes retained physical and functional interaction with the pol γ accessory subunit (p55), and none of the six mutants exhibited defects in misinsertion fidelity in vitro. However, differential DNA binding by these mutants suggests a possible orientation of the DNA with respect to the polymerase during catalysis. To our knowledge this study represents the first structure-function analysis of the thumb subdomain in pol γ and examines the consequences of mitochondrial disease mutations in this region.As the only DNA polymerase found in animal cell mitochondria, DNA polymerase γ (pol γ)³ bears sole responsibility for DNA synthesis in all replication and repair transactions involving mitochondrial DNA (1, 2). Mammalian cell pol γ is a heterotrimeric complex composed of one catalytic subunit of 140 kDa (p140) and two 55-kDa accessory subunits (p55) that form a dimer (3). The catalytic subunit contains an N-terminal exonuclease domain connected by a linker region to a C-terminal polymerase domain. Whereas the exonuclease domain contains essential motifs I, II, and III for its activity, the polymerase domain comprising the thumb, palm, and finger subdomains contains motifs A, B, and C that are crucial for polymerase activity. The catalytic subunit is a family A DNA polymerase that includes bacterial pol I and T7 DNA polymerase and possesses DNA polymerase, 3′ → 5′ exonuclease, and 5′-deoxyribose phosphate lyase activities (for review, see Refs. 1 and 2). The 55-kDa accessory subunit (p55) confers processive DNA synthesis and tight binding of the pol γ complex to DNA (4, 5).Depletion of mtDNA as well as the accumulation of deletions and point mutations in mtDNA have been observed in several mitochondrial disorders (for review, see Ref. 6). mtDNA depletion syndromes are caused by defects in nuclear genes responsible for replication and maintenance of the mitochondrial genome (7). Mutation of POLG, the gene encoding the catalytic subunit of pol γ, is frequently involved in disorders linked to mutagenesis of mtDNA (8, 9). Presently, more than 150 point mutations in POLG are linked with a wide variety of mitochondrial diseases, including the autosomal dominant (ad) and recessive forms of progressive external ophthalmoplegia (PEO), Alpers syndrome, parkinsonism, ataxia-neuropathy syndromes, and male infertility (tools.niehs.nih.gov/polg) (9).Alpers syndrome, a hepatocerebral mtDNA depletion disorder, and myocerebrohepatopathy are rare heritable autosomal recessive diseases primarily affecting young children (10–12). These diseases generally manifest during the first few weeks to years of life, and symptoms gradually develop in a stepwise manner eventually leading to death. Alpers syndrome is characterized by refractory seizures, psychomotor regression, and hepatic failure (11, 12). Mutation of POLG was first linked to Alpers syndrome in 2004 (13), and to date 45 different point mutations in POLG (18 localized to the polymerase domain) are associated with Alpers syndrome (9, 14, 15). However, only two Alpers mutations (A467T and W748S, both in the linker region) have been biochemically characterized (16, 17).During the initial cloning and sequencing of the human, Drosophila, and chicken pol γ genes, we noted a highly conserved region N-terminal to motif A in the polymerase domain that was specific to pol γ (18). This region corresponds to part of the thumb subdomain that tracks DNA into the active site of both Escherichia coli pol I and T7 DNA polymerase (19–21). A high concentration of disease mutations, many associated with Alpers syndrome, is found in the thumb subdomain.Here we investigated six mitochondrial disease mutations clustered in the N-terminal portion of the polymerase domain of the enzyme (Fig. 1A). Four mutations (G848S, c.2542g→a; T851A, c.2551a→g; R852C, c.2554c→t; R853Q, c.2558g→a) reside in the thumb subdomain and two (Q879H, c.2637g→t and T885S, c.2653a→t) are located in the palm subdomain. These mutations are associated with Alpers, PEO, mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), ataxia-neuropathy syndrome, Leigh syndrome, and myocerebrohepatopathy (

Mitofusins and OPA1 Mediate Sequential Steps in Mitochondrial Membrane Fusion

Mitochondrial fusion requires the coordinated fusion of the outer and inner membranes. Three large GTPases—OPA1 and the mitofusins Mfn1 and Mfn2—are essential for the fusion of mammalian mitochondria. OPA1 is mutated in dominant optic atrophy, a neurodegenerative disease of the optic nerve. In yeast, the OPA1 ortholog Mgm1 is required for inner membrane fusion in vitro; nevertheless, yeast lacking Mgm1 show neither outer nor inner membrane fusion in vivo, because of the tight coupling between these two processes. We find that outer membrane fusion can be readily visualized in OPA1-null mouse cells in vivo, but these events do not progress to inner membrane fusion. Similar defects are found in cells lacking prohibitins, which are required for proper OPA1 processing. In contrast, double Mfn-null cells show neither outer nor inner membrane fusion. Mitochondria in OPA1-null cells often contain multiple matrix compartments bounded together by a single outer membrane, consistent with uncoupling of outer versus inner membrane fusion. In addition, unlike mitofusins and yeast Mgm1, OPA1 is not required on adjacent mitochondria to mediate membrane fusion. These results indicate that mammalian mitofusins and OPA1 mediate distinct sequential fusion steps that are readily uncoupled, in contrast to the situation in yeast.     

Mitochondrial DNA Variation Dictates Expressivity and Progression of Nuclear DNA Mutations Causing Cardiomyopathy

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Anomalous Diffusion Induced by Cristae Geometry in the Inner Mitochondrial Membrane

Diffusion of inner membrane proteins is a prerequisite for correct functionality of mitochondria. The complicated structure of tubular, vesicular or flat cristae and their small connections to the inner boundary membrane impose constraints on the mobility of proteins making their diffusion a very complicated process. Therefore we investigate the molecular transport along the main mitochondrial axis using highly accurate computational methods. Diffusion is modeled on a curvilinear surface reproducing the shape of mitochondrial inner membrane (IM). Monte Carlo simulations are carried out for topologies resembling both tubular and lamellar cristae, for a range of physiologically viable crista sizes and densities. Geometrical confinement induces up to several-fold reduction in apparent mobility. IM surface curvature per se generates transient anomalous diffusion (TAD), while finite and stable values of projected diffusion coefficients are recovered in a quasi-normal regime for short- and long-time limits. In both these cases, a simple area-scaling law is found sufficient to explain limiting diffusion coefficients for permeable cristae junctions, while asymmetric reduction of the junction permeability leads to strong but predictable variations in molecular motion rate. A geometry-based model is given as an illustration for the time-dependence of diffusivity when IM has tubular topology. Implications for experimental observations of diffusion along mitochondria using methods of optical microscopy are drawn out: a non-homogenous power law is proposed as a suitable approach to TAD. The data demonstrate that if not taken into account appropriately, geometrical effects lead to significant misinterpretation of molecular mobility measurements in cellular curvilinear membranes.