Respiratory chain complexes and membrane fatty acids composition in rat testis mitochondria throughout development and ageing

The impact of mitochondrial impairments on sperm function and male fertility: a systematic review

BACKGROUND

Besides adenine triphosphate (ATP) production for sustaining motility, the mitochondria of sperm also host other critical cellular functions during germ cell development and fertilization including calcium homeostasis, generation of reactive oxygen species (ROS), apoptosis, and in some cases steroid hormone biosynthesis. Normal mitochondrial membrane potential with optimal mitochondrial performance is essential for sperm motility, capacitation, acrosome reaction, and DNA integrity.

RESULTS

Defects in the sperm mitochondrial function can severely harm the fertility potential of males. The role of sperm mitochondria in fertilization and its final fate after fertilization is still controversial. Here, we review the current knowledge on human sperm mitochondria characteristics and their physiological and pathological conditions, paying special attention to improvements in assistant reproductive technology and available treatments to ameliorate male infertility.

CONCLUSION

Although mitochondrial variants associated with male infertility have potential clinical use, research is limited. Further understanding is needed to determine how these characteristics lead to adverse pregnancy outcomes and affect male fertility potential.

Uterus infantilis: a novel phenotype associated with AARS2 new genetic variants. A case report

Objectives

To report the first Mexican case with two novel AARS2 mutations causing primary ovarian failure, uterus infantilis, and early-onset dementia secondary to leukoencephalopathy.

Methods

Detailed clinical, clinimetric, neuroimaging features, muscle biopsy with biochemical assays of the main oxidative phosphorylation complexes activities, and molecular studies were performed on samples from a Mexican female.

Results

We present a 41-year-old female patient with learning difficulties since childhood and primary amenorrhea who developed severe cognitive, motor, and behavioral impairment in early adulthood. Neuroimaging studies revealed frontal leukoencephalopathy with hypometabolism at the fronto-cerebellar cortex and caudate nucleus. Uterus infantilis was detected on ultrasound study. Clinical exome sequencing identified two novel variants, NM_020745:c.2864G>A (p.W955^*) and NM_020745:c.1036C>A (p.P346T, p.P346Wfs^*18), in AARS2. Histopathological and biochemical studies on muscle biopsy revealed mitochondrial disorder with cytochrome C oxidase (COX) deficiency.

Conclusions

Several adult-onset cases of leukoencephalopathy and ovarian failure associated with AARS2 variants have been reported. To our best knowledge, none of them showed uterus infantilis. Here we enlarge the genetic and phenotypic spectrum of AARS2-related dementia with leukoencephalopathy and ovarian failure and contribute with detailed clinical, clinometric, neuroimaging, and molecular studies to disease and novel molecular variants characterization.

Comparative analysis unveils the cadmium-induced reproductive toxicity on the testes of Pardosa pseudoannulata

Cadmium (Cd) pollution is one of the most serious heavy metal pollutions in the world, which has been demonstrated to cause different toxicities to living organisms. Cd has been widely suggested to cause reproductive toxicity to vertebrates, yet its reproductive toxicity to invertebrates is not comprehensive. In this study, the wolf spider Pardosa pseudoannulata was used as a bioindicator to evaluate the male reproductive toxicity of invertebrates under Cd stress. Cd stress had no effect on the color, size and length of testis. However, Cd significantly increased the contents of catalase, glutathione peroxidase and malondialdehyde, the antioxidants in the testis of P. pseudoannulata. Then we analyzed the transcriptome of testis exposed to Cd, and identified a total of 4739 differentially expressed genes (DEGs) compared to control, with 2368 up-regulated and 2371 down-regulated. The enrichment analysis showed that Cd stress could affect spermatogenesis, sperm motility, post-embryonic development, oxidative phosphorylation and metabolism and synthesis of male reproductive components. At the same time, the protein-protein interaction network was constructed with the generated DEGs. Combined with the enrichment analysis of key modules, it revealed that Cd stress could further affect the metabolic process in testis. In general, the analysis of testicular damage and transcriptome under Cd stress can provide a novel insight into the reproductive toxicity of Cd on rice filed arthropods and offer a reference for the protection of rice filed spiders under Cd pollution.

LINC00116 codes for a mitochondrial peptide linking respiration and lipid metabolism

Short peptides are encoded in genomes of all organisms and have important functions. Due to the small size of such open reading frames, they are frequently overlooked by automatic genome annotation. We investigated the gene that was misannotated as long noncoding RNA LINC00116 and demonstrated that this gene codes for a 56-amino-acid-long peptide, Mtln, which is localized in mitochondria. Inactivation of the Mtln coding gene leads to reduction of oxygen consumption attributed to respiratory complex I activity and perturbs lipid composition of the cell. This influence is mediated by Mtln interaction with NADH-dependent cytochrome b5 reductase. Disruption of the mitochondrial localization of the latter phenocopies Mtln inactivation.

Genes coding for small peptides have been frequently misannotated as long noncoding RNA (lncRNA) genes. Here we have demonstrated that one such transcript is translated into a 56-amino-acid-long peptide conserved in chordates, corroborating the work published while this manuscript was under review. The Mtln peptide could be detected in mitochondria of mouse cell lines and tissues. In line with its mitochondrial localization, lack of the Mtln decreases the activity of mitochondrial respiratory chain complex I. Unlike the integral components and assembly factors of NADH:ubiquinone oxidoreductase, Mtln does not alter its enzymatic activity directly. Interaction of Mtln with NADH-dependent cytochrome b5 reductase stimulates complex I functioning most likely by providing a favorable lipid composition of the membrane. Study of Mtln illuminates the importance of small peptides, whose genes might frequently be misannotated as lncRNAs, for the control of vitally important cellular processes.

Responses of gonadal transcriptome and physiological analysis following exposure to 17α-ethynylestradiol in adult rare minnow Gobiocypris rarus

17α-ethynylestradiol (EE2), a synthetic estrogen commonly used in the oral contraceptive pills, disrupts the sexual differentiation, gonadal development and reproduction in aquatic species. Nowadays aquatic species and even humans still have the potential risks of exposure to EE2. However, the mechanism of EE2 endocrine disruption is still unclear. Aiming to elucidate molecular mechanisms, we analyzed transcriptome profiling of gonads, gonadal histology and the sex steroid hormones in response to EE2 in G. rarus. Through this study, we obtained eight RNA-Seq libraries upon EE2 exposure, and found some key genes and pathways in correlation with the disruption effects of EE2. We found EE2 could disrupt oocyte development and spermatogenesis in adult G. rarus, and EE2 has more obvious disruption effects on male G. rarus than females. Interestingly, EE2 was indicated to be an exogenous DPC-inducing agent and ppp2r3b was suggested to be a spermatogenesis candidate gene in rare minnow. The differential gene expressions of rps30, samp9, ppp2r3b and spartan upon EE2 exposure suggest EE2's disruption effects on gonads could attribute to altered pathways of translation, ribosome biogenesis and cell division.

Mitochondrial membrane lipid remodeling in pathophysiology: a new target for diet and therapeutic interventions

Mitochondria are arbiters in the fragile balance between cell life and death. These organelles present an intricate membrane system, with a peculiar lipid composition and displaying transverse as well as lateral asymmetry. Some lipids are synthesized inside mitochondria, while others have to be imported or acquired in the form of precursors. Here, we review different processes, including external interventions (e.g., diet) and a range of biological events (apoptosis, disease and aging), which may result in alterations of mitochondrial membrane lipid content. Cardiolipin, the mitochondria lipid trademark, whose biosynthetic pathway is highly regulated, will deserve special attention in this review. The modulation of mitochondrial membrane lipid composition, especially by diet, as a therapeutic strategy for the treatment of some pathologies will be also addressed.

High-sucrose diet increases ROS generation, FFA accumulation, UCP2 level, and proton leak in liver mitochondria

Obesity, a risk factor for insulin resistance, contributes to the development of type 2 diabetes and cardiovascular diseases. The relationship between increased levels of free fatty acids in the liver mitochondria, mitochondrial function, and ROS generation in rat model of obesity induced by a high-sucrose diet was not sufficiently established. We determined how the bioenergetic functions and ROS generation of the mitochondria respond to a hyperlipidemic environment. Mitochondria from sucrose-fed rats generated H(2)O(2) at a higher rate than the control mitochondria. Adding fatty acid-free bovine serum albumin to mitochondria from sucrose-fed rats significantly reduced the rate of H(2)O(2) generation. In contrast, adding exogenous oleic or linoleic acid exacerbated the rate of H(2)O(2) generation in both sucrose-fed and control mitochondria, and the mitochondria from sucrose-fed rats were more sensitive than the control mitochondria. The increased rate of H(2)O(2) generation in sucrose-fed mitochondria corresponded to decreased levels of reduced GSH and vitamin E and increased levels of Cu/Zn-SOD in the intermembrane space. There was no difference between the levels of lipid peroxidation and protein carbonylation in the two types of mitochondria. In addition to the normal activity of Mn-SOD, GPX and catalase detected an increased activity of complex II, and upregulation of UCP2 was observed in mitochondria from sucrose-fed rats, all of which may accelerate respiration rates and reduce generation of ROS. In turn, these effects may protect the mitochondria of sucrose-fed rats from oxidative stress and preserve their function and integrity. However, in whole liver these adaptive mechanisms of the mitochondria were inefficient at counteracting redox imbalances and inhibiting oxidative stress outside of the mitochondria.

High fat diet-induced changes in mouse muscle mitochondrial phospholipids do not impair mitochondrial respiration despite insulin resistance

Background

Type 2 diabetes mellitus and muscle insulin resistance have been associated with reduced capacity of skeletal muscle mitochondria, possibly as a result of increased intake of dietary fat. Here, we examined the hypothesis that a prolonged high-fat diet consumption (HFD) increases the saturation of muscle mitochondrial membrane phospholipids causing impaired mitochondrial oxidative capacity and possibly insulin resistance.

Methodology

C57BL/6J mice were fed an 8-week or 20-week low fat diet (10 kcal%; LFD) or HFD (45 kcal%). Skeletal muscle mitochondria were isolated and fatty acid (FA) composition of skeletal muscle mitochondrial phospholipids was analyzed by thin-layer chromatography followed by GC. High-resolution respirometry was used to assess oxidation of pyruvate and fatty acids by mitochondria. Insulin sensitivity was estimated by HOMA-IR.

Principal Findings

At 8 weeks, mono-unsaturated FA (16∶1n7, 18∶1n7 and 18∶1n9) were decreased (−4.0%, p<0.001), whereas saturated FA (16∶0) were increased (+3.2%, p<0.001) in phospholipids of HFD vs. LFD mitochondria. Interestingly, 20 weeks of HFD descreased mono-unsaturated FA while n-6 poly-unsaturated FA (18∶2n6, 20∶4n6, 22∶5n6) showed a pronounced increase (+4.0%, p<0.001). Despite increased saturation of muscle mitochondrial phospholipids after the 8-week HFD, mitochondrial oxidation of both pyruvate and fatty acids were similar between LFD and HFD mice. After 20 weeks of HFD, the increase in n-6 poly-unsaturated FA was accompanied by enhanced maximal capacity of the electron transport chain (+49%, p = 0.002) and a tendency for increased ADP-stimulated respiration, but only when fuelled by a lipid-derived substrate. Insulin sensitivity in HFD mice was reduced at both 8 and 20 weeks.

Conclusions/Interpretation

Our findings do not support the concept that prolonged HF feeding leads to increased saturation of skeletal muscle mitochondrial phospholipids resulting in a decrease in mitochondrial fat oxidative capacity and (muscle) insulin resistance.

Aging and exercise training reduce testes microvascular PO2 and alter vasoconstrictor responsiveness in testicular arterioles

Testicular function and associated testosterone concentration decline with advancing age, and an impaired O₂ supply may contribute, in part, to this reduction. We hypothesized that there would be a reduced microvascular Po₂ (Po₂(m)) in the testes from aged rats, and this reduced Po₂(m) would be associated with impaired vasomotor control in isolated resistance arterioles. In addition, given the positive effect of exercise on microvascular Po₂ and arteriolar function, we further hypothesized that there would be an enhanced Po₂(m) in the testes from aged animals after aerobic exercise training. Testicular Po₂(m) was measured in vivo via phosphorescence quenching in young and aged sedentary (SED) and exercise-trained (ET; 15 m/min treadmill walking, 15-degree incline, 5 days/wk for 10 wk) male Fischer-344 rats. Vasoconstriction to α-adrenergic [norepinephrine (NE) and phenylephrine (PE)] and myogenic stimuli in testicular arterioles was assessed in vitro. In the SED animals, testicular Po₂(m) was reduced by ∼50% with old age (aged SED 11.8 ± 1.9 vs. young SED 22.1 ± 1.1 mmHg; P = 0.0001). Contrary to our hypothesis, exercise training did not alter Po₂(m) in the aged group and reduced testicular Po₂(m) in the young animals, abolishing age-related differences (young ET, 10.0 ± 0.8 vs. aged ET, 10.7 ± 0.9 mmHg; P = 0.37). Vasoconstrictor responsiveness to NE and PE was diminished in aged compared with young (NE: young SED, 58 ± 2 vs. aged SED, 47 ± 2%; P = 0.001) (PE: young SED, 51 ± 3 vs. aged SED, 36 ± 5%; P = 0.008). Exercise training did not alter maximal vasoconstriction to NE in young or aged groups. In summary, advancing age is associated with a reduced testis Po₂(m) and impaired adrenergic vasoconstriction. The diminished testicular microvascular driving pressure of O₂ and associated vascular dysfunction provides mechanistic insight into the old age-related decrease in testicular function, and a reduced Po₂(m) may contribute, in part, to reduced fertility markers after exercise training.

Proton leak modulation in testicular mitochondria affects reactive oxygen species production and lipid peroxidation

Mitochondrial proton leak can account for almost 20% of oxygen consumption and it is generally accepted that this process contributes to basal metabolism. In order to clarify the role of basal proton leak in testicular mitochondria, we performed a comparative study with kidney and liver mitochondrial fractions. Proton leak stimulated by linoleic acid and inhibited by guanosine diphosphate (GDP) was detected, in a manner that was correlated with protein levels for uncoupling protein 2 (UCP2) in the three fractions. Modulation of proton leak had an effect on reactive oxygen species production as well as on lipid peroxidation, and this effect was also tissue-dependent. However, a possible role for the adenine nucleotide transporter (ANT) in testicular mitochondria proton leak could not be excluded. The modulation of proton leak appears as a possible and attractive target to control oxidative stress with implications for male gametogenesis.

Retinoylation reactions are inversely related to the cardiolipin level in testes mitochondria from hypothyroid rats

The effect of hypothyroidism, induced by 6-n-propyl-2-thiouracil (PTU) administration to rats, on the retinoylation reaction and oxidative status was investigated in rat-testes mitochondria. In hypothyroid mitochondria, when compared to euthyroid controls, we found a noticeable increase in the amount of all-trans-retinoic acid (atRA) bound to mitochondrial proteins by an acylation process (34.2 +/- 1.9 pmoles atRA/mg protein/360 min and 22.2 +/- 1.7 pmoles atRA/mg protein/360 min, respectively). This increase, which was time- and temperature-dependent, was accompanied by a strong reduction in the cardiolipin (CL) amount in the mitochondrial membranes of hypothyroid (2.6 +/- 0.2%) as compared to euthyroid rats (4.5 +/- 0.5%) Conversely, a decreased retinoylation reaction was observed when CL liposomes were added to mitochondria or mitoplasts from both euthyroid and hypothyroid rats, thus confirming a role of CL in the retinoylation process. In mitochondria from the latter animals an increase of the level of oxidized CL occurred. The ATP level, which was reduced in hypothyroid mitochondria (27.3 +/- 4.1 pmoles ATP/mg protein versus 67.1 +/- 8.3 pmoles ATP/mg protein of euthyroid animals), was surprisingly increased in mitochondria by the retinoylation reaction in the presence of 100 nM atRA (481.5 +/- 19.3 pmoles ATP/mg protein of hypothyroid animals versus 84.7 +/- 7.7 pmoles ATP/mg protein of euthyroid animals). Overall, in hypothyroid rat-testes mitochondria the increase in retinoylation activity correlates with a significant depletion of the CL level, due to a peroxidation of this lipid. In addition, an enhanced production of reactive oxygen species was observed.

Adrenal glands and testes as steroidogenic tissue are affected by retinoylation reaction

This study was undertaken to better understand the physiological role of the retinoylation process in steroidogenic tissues. In adrenal gland mitochondria, the retinoylation extent was found equal to that of testes mitochondria but without ATP in the incubation buffer. We pointed out that the endogenous mitochondrial ATP in adrenal glands is much higher than in testes, about 1.3 x 10(-2) M and 5.2 x 10(-8) M, respectively. In addition, less CoASH is required for the maximal acylation activity of the retinoyl moiety to protein(s) compared to testes. The fatty acid analysis revealed a different composition of mitochondrial membranes of these two tissues. Among the different values of fatty acids, it is important to note that adrenal glands contain a much higher amount of C18:0 and a much lower amount of C22:5 omega6 and C22:6 omega3 than testes in the mitochondrial membranes. In addition, there were also differences in arachidonic acid (ARA, C20:4 omega6) content between adrenal glands and testes mitochondria. These different values in the fatty acids composition should explain the different extent of the retinoylation process between the two organs.

Mitochondria and ageing in Drosophila

Studies in different organisms have revealed that ageing is a complex process involving a tight regulation of gene expression. Among other features, ageing organisms generally display an increased oxidative stress and a decreased mitochondrial function. The increase in oxidative stress can be attributable to reactive oxygen species, which are mainly produced by mitochondria as a by-product of energy metabolism. Consistent with these data, mitochondria have been suggested to play a significant role in lifespan determination. The fruitfly Drosophila melanogaster is a well-suited organism to study ageing as it is relatively short-lived, mainly composed of post-mitotic cells, has sequenced nuclear and mitochondrial genomes, and multiple genetic tools are available. It has been used in genome-wide studies to unveil the molecular signature of ageing, in different feeding and dietary restriction protocols and in overexpression and down-regulation studies to examine the effect of specific compounds or genes/proteins on lifespan. Here we review the various features linking mitochondria and ageing in Drosophila melanogaster.

Analysis of age-associated changes in mitochondrial free radical generation by rat testis

Throughout spermatogenesis, mitochondria undergo a morphological and functional differentiation. Mitochondria are involved in the production of reactive oxygen species (ROS), considered one of the mediators of ageing. Particularly, lipid peroxidation is regarded as a major phenomenon by which ROS can impair cellular function. In the present study, we examined the production of superoxide anion, superoxide dismutase activity and the effect of Fe(2+)/ascorbate induced-lipid peroxidation on the respiratory chain activities of testis mitochondria throughout the process of spermatogenesis and ageing. Mitochondria from rat testes generated superoxide anion, mainly using NADH as substrate, which increased according to age. The activity of SOD is age-dependent and greatly stimulated during the first wave of spermatogenesis, but decreases in adulthood and old age. TBARS concentration was also markedly increased by ageing. The activity of mitochondrial respiratory chain complexes is differentially affected by oxidative stress induced by iron/ascorbate, succinate-dehydrogenase activity being less vulnerable than that of NADH-dehydrogenase and cytochrome c oxidase. The data suggest that ageing is accompanied by reduced activity of SOD, leading to excessive oxidative stress and enhanced lipid peroxidation that compromises the functionality of the electron transport chain. The data support the concept that mitochondrial function is an important determinant in ageing.

Aging impact on biochemical activities and gene expression of Drosophila melanogaster mitochondria

The consequences of aging are characterized by a decline in the main cellular functions, including those of the mitochondria. Although these consequences have been much studied, efforts have often focused solely on a few parameters used to assess the "state" of mitochondrial function during aging. We performed comparative measurements of several parameters in young (a few days) and old (8 and 12 weeks) adult male Drosophila melanogaster: respiratory complex activities, mitochondrial respiration, ATP synthesis, lipid composition of the inner membrane, concentrations of respiratory complex subunits, expression of genes (nuclear and mitochondrial) coding for mitochondrial proteins. Our results show that, in the mitochondria of "old" flies, the activities of three respiratory complexes (I, III, IV) are greatly diminished, ATP synthesis is decreased, and the lipid composition of the inner membrane (fatty acids, cardiolipin) is modified. However, the respiration rate and subunit concentrations measured by Western blot are unaffected. Although cellular mitochondrial DNA (mtDNA) content remains constant, there is a decrease in concentrations of nuclear and mitochondrial transcripts apparently coordinated. The expression of nuclear genes encoding the transcription factors TFAM, TFB1, TFB2, and DmTTF, which are essential for the maintenance and expression of mtDNA are also decreased. The decrease in nuclear and mitochondrial transcript concentrations may be one of the principal effects of aging on mitochondria, and could explain observed decreases in mitochondrial efficiency.