High OXPHOS efficiency in RA-FUdr-differentiated SH-SY5Y cells: involvement of cAMP signalling and respiratory supercomplexes

Neurons are highly dependent on mitochondria to meet their bioenergetic needs and understanding the metabolic changes during the differentiation process is crucial in the neurodegeneration context. Several in vitro approaches have been developed to study neuronal differentiation and bioenergetic changes. The human SH-SY5Y cell line is a widely used cellular model and several differentiation protocols have been developed to induce a neuron-like phenotype including retinoic acid (RA) treatment. In this work we obtained a homogeneous functional population of neuron-like cells by a two-step differentiation protocol in which SH-SY5Y cells were treated with RA plus the mitotic inhibitor 2-deoxy-5-fluorouridine (FUdr). RA-FUdr treatment induced a neuronal phenotype characterized by increased expression of neuronal markers and electrical properties specific to excitable cells. In addition, the RA-FUdr differentiated cells showed an enrichment of long chain and unsaturated fatty acids (FA) in the acyl chain composition of cardiolipin (CL) and the bioenergetic analysis evidences a high coupled and maximal respiration associated with high mitochondrial ATP levels. Our results suggest that the observed high oxidative phosphorylation (OXPHOS) capacity may be related to the activation of the cyclic adenosine monophosphate (cAMP) pathway and the assembly of respiratory supercomplexes (SCs), highlighting the change in mitochondrial phenotype during neuronal differentiation.

Mitochondria Deregulations in Cancer Offer Several Potential Targets of Therapeutic Interventions

Mitochondria play a key role in cancer and their involvement is not limited to the production of ATP only. Mitochondria also produce reactive oxygen species and building blocks to sustain rapid cell proliferation; thus, the deregulation of mitochondrial function is associated with cancer disease development and progression. In cancer cells, a metabolic reprogramming takes place through a different modulation of the mitochondrial metabolic pathways, including oxidative phosphorylation, fatty acid oxidation, the Krebs cycle, glutamine and heme metabolism. Alterations of mitochondrial homeostasis, in particular, of mitochondrial biogenesis, mitophagy, dynamics, redox balance, and protein homeostasis, were also observed in cancer cells. The use of drugs acting on mitochondrial destabilization may represent a promising therapeutic approach in tumors in which mitochondrial respiration is the predominant energy source. In this review, we summarize the main mitochondrial features and metabolic pathways altered in cancer cells, moreover, we present the best known drugs that, by acting on mitochondrial homeostasis and metabolic pathways, may induce mitochondrial alterations and cancer cell death. In addition, new strategies that induce mitochondrial damage, such as photodynamic, photothermal and chemodynamic therapies, and the development of nanoformulations that specifically target drugs in mitochondria are also described. Thus, mitochondria-targeted drugs may open new frontiers to a tailored and personalized cancer therapy.

Mitochondrial Complex I, a Possible Sensible Site of cAMP Pathway in Aging

In mammals during aging, reactive oxygen species (ROS), produced by the mitochondrial respiratory chain, cause oxidative damage of macromolecules leading to respiratory chain dysfunction, which in turn increases ROS mitochondrial production. Many efforts have been made to understand the role of oxidative stress in aging and age-related diseases. The complex I of the mitochondrial respiratory chain is the major source of ROS production and its dysfunctions have been associated with several forms of neurodegeneration, other common human diseases and aging. Complex I-ROS production and complex I content have been proposed as the major determinants for longevity. The cAMP signal has a role in the regulation of complex I activity and the decrease of ROS production. In the last years, an increasing number of studies have attempted to activate cAMP signaling to treat age-related diseases associated with mitochondrial dysfunctions and ROS production. This idea comes from a long-line of studies showing a main role of cAMP signal in the memory consolidation mechanism and in the regulation of mitochondrial functions. Here, we discuss several evidences on the possible connection between complex I and cAMP pathway in the aging process.

Ovarian Cancer: A Landscape of Mitochondria with Emphasis on Mitochondrial Dynamics

Ovarian cancer (OC) represents the main cause of death from gynecological malignancies in western countries. Altered cellular and mitochondrial metabolism are considered hallmarks in cancer disease. Several mitochondrial aspects have been found altered in OC, such as the oxidative phosphorylation system, oxidative stress and mitochondrial dynamics. Mitochondrial dynamics includes cristae remodeling, fusion, and fission processes forming a dynamic mitochondrial network. Alteration of mitochondrial dynamics is associated with metabolic change in tumour development and, in particular, the mitochondrial shaping proteins appear also to be responsible for the chemosensitivity and/or chemoresistance in OC. In this review a focus on the mitochondrial dynamics in OC cells is presented.

Beneficial effects of SS-31 peptide on cardiac mitochondrial dysfunction in tafazzin knockdown mice

Barth Syndrome (BTHS), a genetic disease associated with early-onset cardioskeletal myopathy, is caused by loss-of-function mutations of the TAFAZZIN gene, which is responsible for remodeling the mitochondrial phospholipid cardiolipin (CL). Deregulation of CL biosynthesis and maturation in BTHS mitochondria result in a dramatically increased monolysocardiolipin (MLCL)/CL ratio associated with bioenergetic dysfunction. One of the most promising therapeutic approaches for BTHS includes the mitochondria-targeted tetrapeptide SS-31, which interacts with CL. Here, we used TAFAZZIN knockdown (Taz^KD) mice to investigate for the first time whether in vivo administration of SS-31 could affect phospholipid profiles and mitochondrial dysfunction. The CL fingerprinting of Taz^KD cardiac mitochondria obtained by MALDI-TOF/MS revealed the typical lipid changes associated with BTHS. Taz^KD mitochondria showed lower respiratory rates in state 3 and 4 together with a decreased in maximal respiratory rates. Treatment of Taz^KD mice with SS-31 improved mitochondrial respiratory capacity and promoted supercomplex organization, without affecting the MLCL/CL ratio. We hypothesize that SS-31 exerts its effect by influencing the function of the respiratory chain rather than affecting CL directly. In conclusion, our results indicate that SS-31 have beneficial effects on improving cardiac mitochondrial dysfunction in a BTHS animal model, suggesting the peptide as future pharmacologic agent for therapy.

Adhesion of Platelets to Colon Cancer Cells Is Necessary to Promote Tumor Development in Xenograft, Genetic and Inflammation Models

Simple Summary

Platelets are small, anucleate, metabolically active cells and they represent an important linkage between tissue damage and inflammatory response. Several studies focused on the central role of platelets in inflammation and tumor development through their direct interaction with other cell types. Mice lacking the vascular adhesion molecules P-selectin exhibited a reduction in tumor metastases. We demonstrated that P-selectin-ablated platelets reduced tumor growth in a xenograft adenocarcinoma model. Furthermore, the lack of P-selectin decreased colon cancer progression in genetic mouse models and in chemically-induced colitis colorectal carcinogenesis. Our results suggest that platelets-cancer cells crosstalk via P-selectin is fundamental for tumor development.

Abstract

Platelets represent the linkage between tissue damage and inflammatory response with a putative role in tumorigenesis. Given the importance of the microenvironment in colon cancer development, we elucidated the eventual role of platelets-cancer cells crosstalk in in vivo colon cancer models. To evaluate the involvement of platelets in intestinal tumorigenesis, we first analyzed if the ablation of β-integrin P-selectin that drives platelets-cell adhesion, would contribute to platelets-colon cancer cell interaction and drive cancer progression. In a xenograft tumor model, we observed that when tumors are inoculated with platelets, the ablation of P-selectin significantly reduced tumor growth compared to control platelets. Furthermore, in genetic models, as well as in chronic colitis-associated colorectal carcinogenesis, P-selectin ablated mice displayed a significant reduction in tumor number and size compared to control mice. Taken together, our data highlights the importance of platelets in the tumor microenvironment for intestinal tumorigenesis. These results support the hypothesis that a strategy aimed to inhibit platelets adhesion to tumor cells are able to block tumor growth and could represent a novel therapeutic approach to colon cancer treatment.

Moringa oleifera Protects SH-SY5YCells from DEHP-Induced Endoplasmic Reticulum Stress and Apoptosis

Moringa oleifera (MO) is a medicinal plant that has been shown to possess antioxidant, anticarcinogenic and antibiotic activities. In a rat model, MO extract (MOe) has been shown to have a protective effect against brain damage and memory decline. As an extending study, here, we have examined the protective effect of MOe against oxidative stress and apoptosis caused in human neuroblastome (SH-SY5Y) cells by di-(2-ethylhexyl) phthalate (DEHP), a plasticizer known to induce neurotoxicity. Our data show that MOe prevents oxidative damage by lowering reactive oxygen species (ROS) formation, restoring mitochondrial respiratory chain complex activities, and, in addition, by modulating the expression of vitagenes, i.e., antioxidant proteins Nrf2 and HO-1. Moreover, MOe prevented neuronal damage by partly inhibiting endoplasmic reticulum (ER) stress response, as indicated by decreased expression of CCAAT-enhancer-binding protein homologous protein (CHOP) and Glucose-regulated protein 78 (GRP78) proteins. MOe also protected SH-SY5Y cells from DEHP-induced apoptosis, preserving mitochondrial membrane permeability and caspase-3 activation. Our findings provide insight into understanding of molecular mechanisms involved in neuroprotective effects by MOe against DEHP damage.

PBMC of Multiple Sclerosis Patients Show Deregulation of OPA1 Processing Associated with Increased ROS and PHB2 Protein Levels

Multiple sclerosis (MS) is an autoimmune disease in which activated lymphocytes affect the central nervous system. Increase of reactive oxygen species (ROS), impairment of mitochondria-mediated apoptosis and mitochondrial alterations have been reported in peripheral lymphocytes of MS patients. Mitochondria-mediated apoptosis is regulated by several mechanisms and proteins. Among others, optic atrophy 1 (OPA1) protein plays a key role in the regulating mitochondrial dynamics, cristae architecture and release of pro-apoptotic factors. Very interesting, mutations in OPA1 gene, have been associated with multiple sclerosis-like disorder. We have analyzed OPA1 and some factors involved in its regulation. Fifteen patients with MS and fifteen healthy control subjects (HC) were enrolled into the study and peripheral blood mononuclear cells (PBMCs) were isolated. H₂O₂ level was measured spectrofluorimetrically, OPA1, PHB2, SIRT3, and OMA1 were analyzed by western blotting. Statistical analysis was performed using Student's t-test. The results showed that PBMC of MS patients were characterized by a deregulation of OPA1 processing associated with increased H₂O₂ production, inactivation of OMA1 and increase of PHB2 protein level. The presented data suggest that the alteration of PHB2, OMA1, and OPA1 processing could be involved in resistance towards apoptosis. These molecular parameters could also be useful to assess disease activity.

Hericium Erinaceus Prevents DEHP-Induced Mitochondrial Dysfunction and Apoptosis in PC12 Cells

Hericium Erinaceus (HE) is a medicinal plant known to possess anticarcinogenic, antibiotic, and antioxidant activities. It has been shown to have a protective effect against ischemia-injury-induced neuronal cell death in rats. As an extending study, here we examined in pheochromocytoma 12 (PC12) cells, whether HE could exert a protective effect against oxidative stress and apoptosis induced by di(2-ethylhexyl)phthalate (DEHP), a plasticizer known to cause neurotoxicity. We demonstrated that pretreatment with HE significantly attenuated DEHP induced cell death. This protective effect may be attributed to its ability to reduce intracellular reactive oxygen species levels, preserving the activity of respiratory complexes and stabilizing the mitochondrial membrane potential. Additionally, HE pretreatment significantly modulated Nrf2 and Nrf2-dependent vitagenes expression, preventing the increase of pro-apoptotic and the decrease of anti-apoptotic markers. Collectively, our data provide evidence of new preventive nutritional strategy using HE against DEHP-induced apoptosis in PC12 cells.

Mitochondrial Dynamics of Proximal Tubular Epithelial Cells in Nephropathic Cystinosis

Nephropathic cystinosis is a rare lysosomal storage disorder caused by mutations in CTNS gene leading to Fanconi syndrome. Independent studies reported defective clearance of damaged mitochondria and mitochondrial fragmentation in cystinosis. Proteins involved in the mitochondrial dynamics and the mitochondrial ultrastructure were analyzed in CTNS-/- cells treated with cysteamine, the only drug currently used in the therapy for cystinosis but ineffective to treat Fanconi syndrome. CTNS-/- cells showed an overexpression of parkin associated with deregulation of ubiquitination of mitofusin 2 and fission 1 proteins, an altered proteolytic processing of optic atrophy 1 (OPA1), and a decreased OPA1 oligomerization. According to molecular findings, the analysis of electron microscopy images showed a decrease of mitochondrial cristae number and an increase of cristae lumen and cristae junction width. Cysteamine treatment restored the fission 1 ubiquitination, the mitochondrial size, number and lumen of cristae, but had no effect on cristae junction width, making CTNS-/- tubular cells more susceptible to apoptotic stimuli.

Prohibitins: A Critical Role in Mitochondrial Functions and Implication in Diseases

Prohibitin 1 (PHB1) and prohibitin 2 (PHB2) are proteins that are ubiquitously expressed, and are present in the nucleus, cytosol, and mitochondria. Depending on the cellular localization, PHB1 and PHB2 have distinctive functions, but more evidence suggests a critical role within mitochondria. In fact, PHB proteins are highly expressed in cells that heavily depend on mitochondrial function. In mitochondria, these two proteins assemble at the inner membrane to form a supra-macromolecular structure, which works as a scaffold for proteins and lipids regulating mitochondrial metabolism, including bioenergetics, biogenesis, and dynamics in order to determine the cell fate, death, or life. PHB alterations have been found in aging and cancer, as well as neurodegenerative, cardiac, and kidney diseases, in which significant mitochondrial impairments have been observed. The molecular mechanisms by which prohibitins regulate mitochondrial function and their role in pathology are reviewed and discussed herein.

Impact of atypical mitochondrial cyclic-AMP level in nephropathic cystinosis

Nephropathic cystinosis (NC) is a rare disease caused by mutations in the CTNS gene encoding for cystinosin, a lysosomal transmembrane cystine/H⁺ symporter, which promotes the efflux of cystine from lysosomes to cytosol. NC is the most frequent cause of Fanconi syndrome (FS) in young children, the molecular basis of which is not well established. Proximal tubular cells have very high metabolic rate due to the active transport of many solutes. Not surprisingly, mitochondrial disorders are often characterized by FS. A similar mechanism may also apply to NC. Because cAMP has regulatory properties on mitochondrial function, we have analyzed cAMP levels and mitochondrial targets in CTNS^-/- conditionally immortalized proximal tubular epithelial cells (ciPTEC) carrying the classical homozygous 57-kb deletion (delCTNS^-/-) or with compound heterozygous loss-of-function mutations (mutCTNS^-/-). Compared to wild-type cells, cystinotic cells had significantly lower mitochondrial cAMP levels (delCTNS^-/- ciPTEC by 56% ± 10.5, P < 0.0001; mutCTNS^-/- by 26% ± 4.3, P < 0.001), complex I and V activities, mitochondrial membrane potential, and SIRT3 protein levels, which were associated with increased mitochondrial fragmentation. Reduction of complex I and V activities was associated with lower expression of part of their subunits. Treatment with the non-hydrolysable cAMP analog 8-Br-cAMP restored mitochondrial potential and corrected mitochondria morphology. Treatment with cysteamine, which reduces the intra-lysosomal cystine, was able to restore mitochondrial cAMP levels, as well as most other abnormal mitochondrial findings. These observations were validated in CTNS-silenced HK-2 cells, indicating a pivotal role of mitochondrial cAMP in the proximal tubular dysfunction observed in NC.

Uncoupling FoxO3A mitochondrial and nuclear functions in cancer cells undergoing metabolic stress and chemotherapy

While aberrant cancer cell growth is frequently associated with altered biochemical metabolism, normal mitochondrial functions are usually preserved and necessary for full malignant transformation. The transcription factor FoxO3A is a key determinant of cancer cell homeostasis, playing a dual role in survival/death response to metabolic stress and cancer therapeutics. We recently described a novel mitochondrial arm of the AMPK-FoxO3A axis in normal cells upon nutrient shortage. Here, we show that in metabolically stressed cancer cells, FoxO3A is recruited to the mitochondria through activation of MEK/ERK and AMPK, which phosphorylate serine 12 and 30, respectively, on FoxO3A N-terminal domain. Subsequently, FoxO3A is imported and cleaved to reach mitochondrial DNA, where it activates expression of the mitochondrial genome to support mitochondrial metabolism. Using FoxO3A^-/- cancer cells generated with the CRISPR/Cas9 genome editing system and reconstituted with FoxO3A mutants being impaired in their nuclear or mitochondrial subcellular localization, we show that mitochondrial FoxO3A promotes survival in response to metabolic stress. In cancer cells treated with chemotherapeutic agents, accumulation of FoxO3A into the mitochondria promoted survival in a MEK/ERK-dependent manner, while mitochondrial FoxO3A was required for apoptosis induction by metformin. Elucidation of FoxO3A mitochondrial vs. nuclear functions in cancer cell homeostasis might help devise novel therapeutic strategies to selectively disable FoxO3A prosurvival activity.

Mitochondria as pharmacological targets in Down syndrome

Mitochondria play a pivotal role in cellular energy-generating processes and are considered master regulators of cell life and death fate. Mitochondrial function integrates signalling networks in several metabolic pathways controlling neurogenesis and neuroplasticity. Indeed, dysfunctional mitochondria and mitochondrial-dependent activation of intracellular stress cascades are critical initiating events in many human neurodegenerative or neurodevelopmental diseases including Down syndrome (DS). It is well established that trisomy of human chromosome 21 can cause DS. DS is associated with neurodevelopmental delay, intellectual disability and early neurodegeneration. Recently, molecular mechanisms responsible for mitochondrial damage and energy deficits have been identified and characterized in several DS-derived human cells and animal models of DS. Therefore, therapeutic strategies targeting mitochondria could have great potential for new treatment regimens in DS. The purpose of this review is to highlight recent studies concerning mitochondrial impairment in DS, focusing on alterations of the molecular pathways controlling mitochondrial function. We will also discuss the effects and molecular mechanisms of naturally occurring and chemically synthetized drugs that exert neuroprotective effects through modulation of mitochondrial function and attenuation of oxidative stress. These compounds might represent novel therapeutic tools for the modulation of energy deficits in DS.

Inhibition of Drp1-mediated mitochondrial fission improves mitochondrial dynamics and bioenergetics stimulating neurogenesis in hippocampal progenitor cells from a Down syndrome mouse model

Functional and structural damages to mitochondria have been critically associated with the pathogenesis of Down syndrome (DS), a human multifactorial disease caused by trisomy of chromosome 21 and associated with neurodevelopmental delay, intellectual disability and early neurodegeneration. Recently, we demonstrated in neural progenitor cells (NPCs) isolated from the hippocampus of Ts65Dn mice -a widely used model of DS - a severe impairment of mitochondrial bioenergetics and biogenesis and reduced NPC proliferation. Here we further investigated the origin of mitochondrial dysfunction in DS and explored a possible mechanistic link among alteration of mitochondrial dynamics, mitochondrial dysfunctions and defective neurogenesis in DS. We first analyzed mitochondrial network and structure by both confocal and transmission electron microscopy as well as by evaluating the levels of key proteins involved in the fission and fusion machinery. We found a fragmentation of mitochondria due to an increase in mitochondrial fission associated with an up-regulation of dynamin-related protein 1 (Drp1), and a decrease in mitochondrial fusion associated with a down-regulation of mitofusin 2 (Mnf2) and increased proteolysis of optic atrophy 1 (Opa1). Next, using the well-known neuroprotective agent mitochondrial division inhibitor 1 (Mdivi-1), we assessed whether the inhibition of mitochondrial fission might reverse alteration of mitochondrial dynamics and mitochondrial dysfunctions in DS neural progenitors cells. We demonstrate here for the first time, that Mdivi-1 restores mitochondrial network organization, mitochondrial energy production and ultimately improves proliferation and neuronal differentiation of NPCs. This research paves the way for the discovery of new therapeutic tools in managing some DS-associated clinical manifestations.

Major pathogenic mechanisms in vascular dementia: Roles of cellular stress response and hormesis in neuroprotection

Vascular dementia (VaD), considered the second most common cause of cognitive impairment after Alzheimer disease in the elderly, involves the impairment of memory and cognitive function as a consequence of cerebrovascular disease. Chronic cerebral hypoperfusion is a common pathophysiological condition frequently occurring in VaD. It is generally associated with neurovascular degeneration, in which neuronal damage and blood-brain barrier alterations coexist and evoke beta-amyloid-induced oxidative and nitrosative stress, mitochondrial dysfunction, and inflammasome- promoted neuroinflammation, which contribute to and exacerbate the course of disease. Vascular cognitive impairment comprises a heterogeneous group of cognitive disorders of various severity and types that share a presumed vascular etiology. The present study reviews major pathogenic factors involved in VaD, highlighting the relevance of cerebrocellular stress and hormetic responses to neurovascular insult, and addresses these mechanisms as potentially viable and valuable as foci of novel neuroprotective methods to mitigate or prevent VaD. © 2016 Wiley Periodicals, Inc.

cAMP regulates the functional activity, coupling efficiency and structural organization of mammalian FOF1 ATP synthase

The present study shows that in isolated mitochondria and myoblast cultures depletion of cAMP, induced by sAC inhibition, depresses both ATP synthesis and hydrolysis by the FOF1 ATP synthase (complex V) of the oxidative phosphorylation system (OXPHOS). These effects are accompanied by the decrease of the respiratory membrane potential, decreased level of FOF1 connecting subunits and depressed oligomerization of the complex. All these effects of sAC inhibition are prevented by the addition of the membrane-permeant 8-Br-cAMP. These results show, for the first time, that cAMP promotes ATP production by complex V and prevents, at the same time, its detour to a mitochondrial membrane leak conductance, which is involved in cell death.

Intramitochondrial adenylyl cyclase controls the turnover of nuclear-encoded subunits and activity of mammalian complex I of the respiratory chain

In mammalian cells the nuclear-encoded subunits of complex I are imported into mitochondria, where they are assembled with mt-DNA encoded subunits in the complex, or exchanged with pre-existing copies in the complex. The present work shows that in fibroblast cultures inhibition by KH7 of cAMP production in the mitochondrial matrix by soluble adenylyl cyclase (sAC) results in decreased amounts of free non-incorporated nuclear-encoded NDUFS4, NDUFV2 and NDUFA9 subunits of the catalytic moiety and inhibition of the activity of complex I. Addition of permeant 8-Br-cAMP prevents this effect of KH7. KH7 inhibits accumulation in isolated rat-liver mitochondria and incorporation in complex I of "in vitro" produced, radiolabeled NDUFS4 and NDUFV2 subunits. 8-Br-cAMP prevents also this effect of KH7. Use of protease inhibitors shows that intramitochondrial cAMP exerts this positive effect on complex I by preventing digestion of nuclear-encoded subunits by mitochondrial protease(s), whose activity is promoted by KH7 and H89, an inhibitor of PKA.

Epigallocatechin-3-gallate prevents oxidative phosphorylation deficit and promotes mitochondrial biogenesis in human cells from subjects with Down's syndrome

A critical role for mitochondrial dysfunction has been proposed in the pathogenesis of Down's syndrome (DS), a human multifactorial disorder caused by trisomy of chromosome 21, associated with mental retardation and early neurodegeneration. Previous studies from our group demonstrated in DS cells a decreased capacity of the mitochondrial ATP production system and overproduction of reactive oxygen species (ROS) in mitochondria. In this study we have tested the potential of epigallocatechin-3-gallate (EGCG) - a natural polyphenol component of green tea - to counteract the mitochondrial energy deficit found in DS cells. We found that EGCG, incubated with cultured lymphoblasts and fibroblasts from DS subjects, rescued mitochondrial complex I and ATP synthase catalytic activities, restored oxidative phosphorylation efficiency and counteracted oxidative stress. These effects were associated with EGCG-induced promotion of PKA activity, related to increased cellular levels of cAMP and PKA-dependent phosphorylation of the NDUFS4 subunit of complex I. In addition, EGCG strongly promoted mitochondrial biogenesis in DS cells, as associated with increase in Sirt1-dependent PGC-1α deacetylation, NRF-1 and T-FAM protein levels and mitochondrial DNA content. In conclusion, this study shows that EGCG is a promoting effector of oxidative phosphorylation and mitochondrial biogenesis in DS cells, acting through modulation of the cAMP/PKA- and sirtuin-dependent pathways. EGCG treatment promises thus to be a therapeutic approach to counteract mitochondrial energy deficit and oxidative stress in DS.

Mild gestational hyperglycemia and the metabolic syndrome in later life

BACKGROUND

Diabetes and obesity, components of the metabolic syndrome, are common longterm complications in women with previous gestational diabetes (pGDM). Long-term follow-up of women with mild gestational hyperglycemia is lacking.

METHODS

Fifty women with previous positive oral glucose challenge test and negative oral glucose tolerance test (pOGCT+OGTT-), 161 with previous normal glucose tolerance (pNGT), and 182 pGDM were studied after 6.5 years from the index pregnancy.

RESULTS

Patients with pGDM showed a worse metabolic pattern than pNGT. Women with pOGCT+OGTT- had significantly higher levels of fasting glucose, homeostasis model assessment (HOMA), percentage of impaired fasting glucose, and low age and high-density lipoprotein (HDL)-cholesterol than pNGT subjects. Prevalence of the metabolic syndrome (MS) was, respectively, sixfold and twofold higher in pGDM and pOGCT+OGTT- than in pNGT. In a Cox proportional hazard model, after multiple adjustments, pGDM was significantly associated with subsequent hyperglycemia (hazard ratio [HR] = 4.2; 95% CI 1.6-11.1), low HDL-cholesterol (HR = 1.7, 1.1-2.8), hypertriglyceridemia (HR = 4.2, 1.2-14.9), hypertension (HR = 2.2, 1.3-3.6), MS (HR = 3.7, 1.3-10.8), while pOGCT+OGTT- was associated with subsequent hyperglycemia (HR = 4.3, 1.3-14.7), and low HDL-cholesterol (HR = 2.0, 1.0-3.8). The metabolic syndrome was present in 52.6% of obese pGDM, 50% of obese pOGCT+OGTT-, and 28.6% of obese pNGT women; the corresponding HRs were, respectively, HR = 2.20, 0.74-6.57 (pGDM), and HR = 3.56, 1.10-11.5 (pOGCT+OGTT-).

CONCLUSIONS

Women who failed the OGCT, but not the OGTT, showed a subsequent worse metabolic pattern than pNGT subjects, independently of confounding factors. In the presence of obesity, the prevalence of the metabolic syndrome was similar to that of obese pGDM women, and almost twofold higher than in obese pNGT controls.

Activation of the cAMP cascade in human fibroblast cultures rescues the activity of oxidatively damaged complex I

A study of the relationship between cAMP/PKA-dependent phosphorylation and oxidative damage of subunits of complex I of the mitochondrial respiratory chain is presented. It is shown that, in fibroblast cultures, PKA-mediated phosphorylation of the NDUFS4 subunit of complex I rescues the activity of the oxidatively damaged complex. Evidence is presented showing that this effect is mediated by phosphorylation-dependent exchange of carbonylated NDUFS4 subunit in the assembled complex with the de novo synthesized subunit. These results indicate a potential use for β-adrenoceptor agonists in preventing/reversing the detrimental effects of oxidative stress in the mitochondrial respiratory system.

The oxidative phosphorylation system in mammalian mitochondria

The chapter provides a review of the state of art of the oxidative phosphorylation system in mammalian mitochondria. The sections of the paper deal with: (i) the respiratory chain as a whole: redox centers of the chain and protonic coupling in oxidative phosphorylation (ii) atomic structure and functional mechanism of protonmotive complexes I, III, IV and V of the oxidative phosphorylation system (iii) biogenesis of oxidative phosphorylation complexes: mitochondrial import of nuclear encoded subunits, assembly of oxidative phosphorylation complexes, transcriptional factors controlling biogenesis of the complexes. This advanced knowledge of the structure, functional mechanism and biogenesis of the oxidative phosphorylation system provides a background to understand the pathological impact of genetic and acquired dysfunctions of mitochondrial oxidative phosphorylation.

Respiratory chain complex I, a main regulatory target of the cAMP/PKA pathway is defective in different human diseases

In mammals, complex I (NADH-ubiquinone oxidoreductase) of the mitochondrial respiratory chain has 31 supernumerary subunits in addition to the 14 conserved from prokaryotes to humans. Multiplicity of structural protein components, as well as of biogenesis factors, makes complex I a sensible pace-maker of mitochondrial respiration. The work reviewed here shows that the cAMP/PKA pathway regulates the biogenesis, assembly and catalytic activity of complex I and mitochondrial oxygen superoxide production. The structural, functional and regulatory complexity of complex I, renders it particularly vulnerable to genetic and sporadic pathological factors. Complex I dysfunction has, indeed, been found, to be associated with several human diseases. Knowledge of the pathogenetic mechanisms of these diseases can help to develop new therapeutic strategies.

Mitochondrial defect and PGC-1α dysfunction in parkin-associated familial Parkinson's disease

Mutations in the parkin gene are expected to play an essential role in autosomal recessive Parkinson's disease. Recent studies have established an impact of parkin mutations on mitochondrial function and autophagy. In primary skin fibroblasts from two patients affected by an early onset Parkinson's disease, we identified a hitherto unreported compound heterozygous mutation del exon2-3/del exon3 in the parkin gene, leading to the complete loss of the full-length protein. In both patients, but not in their heterozygous parental control, we observed severe ultrastructural abnormalities, mainly in mitochondria. This was associated with impaired energy metabolism, deregulated reactive oxygen species (ROS) production, resulting in lipid oxidation, and peroxisomal alteration. In view of the involvement of parkin in the mitochondrial quality control system, we have investigated upstream events in the organelles' biogenesis. The expression of the peroxisome proliferator-activated receptor gamma-coactivator 1-alpha (PGC-1α), a strong stimulator of mitochondrial biogenesis, was remarkably upregulated in both patients. However, the function of PGC-1α was blocked, as revealed by the lack of its downstream target gene induction. In conclusion, our data confirm the role of parkin in mitochondrial homeostasis and suggest a potential involvement of the PGC-1α pathway in the pathogenesis of Parkinson's disease. This article is part of a Special Issue entitled: Translating nuclear receptors from health to disease.

T16189C mitochondrial DNA variant is associated with metabolic syndrome in Caucasian subjects

OBJECTIVES

Different nuclear genes are thought to be involved in the regulation of the complex phenotype of metabolic syndrome (MS) and their number is increasing. A mutation in mitochondrial DNA (mtDNA), T4291C in transfer RNA isoleucine (tRNAile), has been associated with MS in a large American family. In addition, a mtDNA T16189C variant, already known to be associated with insulin resistance and type 2 diabetes mellitus in Caucasians, seems to underlie susceptibility to MS in the Chinese population. Our aim was to verify the T4291C and T16189C variants in subjects affected by different phenotypes of MS.

METHODS

Seventy patients with MS and 35 healthy individuals were investigated for the presence of the mtDNA variants by polymerase chain reaction-restriction fragment length polymorphism analysis.

RESULTS

The T4291C variant was absent in patients and in controls. The T16189C variant was more frequent in patients with MS than in control subjects (21.4% versus 5.7%, P<0.04) and was associated with hypertension (P=0.01), waist circumference (P=0.02), body mass index (P=0.009), visceral fat thickness (P=0.04), homeostasis model assessment (P=0.03), and the number of MS diagnostic criteria (P=0.01).

CONCLUSION

The mtDNA T16189C variant is associated with MS and its different clinical expressions. Prospective studies are warranted to establish the clinical relevance of this association.

cAMP/Ca2+ response element-binding protein plays a central role in the biogenesis of respiratory chain proteins in mammalian cells

In mammalian cells, promotion of mitochondrial biogenesis by various agents involves cAMP and Ca(2+)-mediated signal transduction pathways. Recruitment of these pathways results in phosphorylation by cAMP and Ca(2+)-dependent protein kinases of cAMP/Ca(2+) response element-binding protein (CREB). Phosphorylation of CREB, bound to transcriptional complexes of target genes, activates a down-stream cascade of transcriptional complexes, which involve in sequence, the nuclear factors TORCs, PGC-1, NRF1 and NRF2, and the mitochondrial factor mitochondrial transcriptional factor A. CREB also binds directly to the D-loop of mitochondrial DNA and activates its expression. Activation of this network of transcriptional complexes results in concerted promotion of the expression of nuclear and mitochondrial genes encoding subunits of oxidative phosphorylation complexes.

cAMP-dependent protein kinase regulates post-translational processing and expression of complex I subunits in mammalian cells

Work is presented on the role of cAMP-dependent protein phosphorylation in post-translational processing and biosynthesis of complex I subunits in mammalian cell cultures. PKA-mediated phosphorylation of the NDUFS4 subunit of complex I promotes in cell cultures in vivo import/maturation in mitochondria of the precursor of this protein. The import promotion appears to be associated with the observed cAMP-dependent stimulation of the catalytic activity of complex I. These effects of PKA are counteracted by activation of protein phosphatase(s). PKA and the transcription factor CREB play a critical role in the biosynthesis of complex I subunits. CREB phosphorylation, by PKA and/or CaMKs, activates at nuclear and mitochondrial level a transcriptional regulatory cascade which promotes the concerted expression of nuclear and mitochondrial encoded subunits of complex I and other respiratory chain proteins.

Genetic and physical mapping of new EST-derived SSRs on the A and B genome chromosomes of wheat

The availability of genetic maps and phenotypic data of segregating populations allows to localize and map agronomically important genes, and to identify closely associated molecular markers to be used in marker-assisted selection and positional cloning. The objective of the present work was to develop a durum wheat intervarietal genetic and physical map based on genomic microsatellite or genomic simple sequence repeats (gSSR) markers and expressed sequence tag (EST)-derived microsatellite (EST-SSR) markers. A set of 122 new EST-SSR loci amplified by 100 primer pairs was genetically mapped on the wheat A and B genome chromosomes. The whole map also comprises 149 gSSR markers amplified by 120 primer pairs used as anchor chromosome loci, two morphological markers (Black colour, Bla1, and spike glaucousness, Ws) and two seed storage protein loci (Gli-A2 and Gli-B2). The majority of SSR markers tested (182) was chromosome-specific. Out of 275 loci 241 loci assembled in 25 linkage groups assigned to the chromosomes of the A and B genome and 34 remained unlinked. A higher percentage of markers (54.4%), localized on the B genome chromosomes, in comparison to 45.6% distributed on the A genome. The whole map covered 1,605 cM. The B genome accounted for 852.2 cM of genetic distance; the A genome basic map spanned 753.1 cM with a minimum length of 46.6 cM for chromosome 5A and a maximum of 156.2 cM for chromosome 3A and an average value of 114.5 cM. The primer sets that amplified two or more loci mapped to homoeologous as well as to non-homoeologous sites. Out of 241 genetically mapped loci 213 (88.4%) were physically mapped by using the nulli-tetrasomic, ditelosomic and a stock of 58 deletion lines dividing the A and B genome chromosomes in 94 bins. No discrepancies concerning marker order were observed but the cytogenetic maps revealed in some cases small genetic distance covered large physical regions. Putative function for mapped SSRs were assigned by searching against GenBank nonredundant database using TBLASTX algorithms.

Mammalian complex I: a regulable and vulnerable pacemaker in mitochondrial respiratory function

In this paper the regulatory features of complex I of mammalian and human mitochondria are reviewed. In a variety of mitotic cell-line cultures, activation in vivo of the cAMP cascade, or direct addition of cAMP, promotes the NADH-ubiquinone oxidoreductase activity of complex I and lower the cellular level of ROS. These effects of cAMP are found to be associated with PKA-mediated serine phosphorylation in the conserved C-terminus of the subunit of complex I encoded by the nuclear gene NDUFS4. PKA mediated phosphorylation of this Ser in the C-terminus of the protein promotes its mitochondrial import and maturation. Mass-spectrometry analysis of the phosphorylation pattern of complex I subunits is also reviewed.

The phosphorylation pattern of bovine heart complex I subunits

The phosphoproteome of bovine heart complex I of the respiratory chain has been analysed with a procedure based on nondenaturing gel electrophoretic separation of complex I from small quantities of mitochondria samples, in-gel digestion, in combination with phosphopeptide enrichment by titanium dioxide and MS. The results, complemented by analyses of purified samples of complex I, showed phosphorylation of five subunits of the complex, 42 kDa (human gene NDUFA10), ESSS, B14.5a (human gene NDUFA7), B14.5b (human gene NDUFC2) and B16.6 (GRIM-19). MS also revealed the presence of phosphorylated programmed cell death protein 8(AIF) in native and purified samples of complex I analysed. The possible physiological relevance of these findings is discussed.

Occurrence of A-kinase anchor protein and associated cAMP-dependent protein kinase in the inner compartment of mammalian mitochondria

Evidence showing the existence in the inner compartment of rat-heart mitochondria of AKAP121 and associated PKA is presented. Immunoblotting analysis and trypsin digestion pattern show that 90% or more of mitochondrial C-PKA, R-PKA and AKAP121 is localized in the inner mitochondrial compartment, when prepared both from isolated mitochondria or cardiomyocyte cultures. This localization is verified by measurement of the specific catalytic activity of PKA, radiolabelling of R-PKA by (32)P-phosphorylated C-PKA and of AKAP by (32)P-phosphorylated R-PKA and electron microscopy of mitochondria exposed to gold-conjugated AKAP121 antibody.

Mutations in structural genes of complex I associated with neurological diseases

This paper summarizes observations on the genetic and biochemical basis of hereditary defects of complex I (NADH-ubiquinone oxidoreductase) of the respiratory chain in human neurological patients. Two different types of functional defects of the complex are described. In one type mutations in the NDUFS1 and NDUFS4 nuclear structural genes of the complex were identified in two unrelated families. Both NDUFS1 and NDUFS4 neurological disorders were transmitted by autosomic recessive inheritance. The two mutations resulted in different impact on cellular metabolism. The NDUFS4 mutation, giving a more severe, fatal pathological pattern, resulted in a defective assembly of the complex and complete suppression of the enzymatic activity. The NDUFS1 mutation, with less severe progressive pathology, caused only partial inhibition of the complex but enhanced production of oxygen free radicals. In the second type of deficiencies extensive mutational analysis did not reveal pathogenic mutations in complex I genes but a decline in the level and activity of complex I, III, and IV were found, apparently associated with alteration in the cardiolipin membrane distribution.

cAMP controls oxygen metabolism in mammalian cells

The impact of cAMP on ROS-balance in human and mammalian cell cultures was studied. cAMP reduced accumulation of ROS induced by serum-limitation, under conditions in which there was no significant change in the activity of scavenger systems. This effect was associated with cAMP-dependent activation of the NADH-ubiquinone oxidoreductase activity of complex I. In fibroblasts from a patient a genetic defect in the 75 kDa FeS-protein subunit of complex I resulted in inhibition of the activity of the complex and enhanced ROS production, which were reversed by cAMP. A missense genetic defect in the NDUFS4 subunit, putative substrate of PKA, suppressed, on the other hand, the activity of the complex and prevented ROS production.

Regulation by the cAMP cascade of oxygen free radical balance in mammalian cells

A study is presented of the effect of the cAMP cascade on oxygen metabolism in mammalian cell cultures. Serum-starvation of the cell cultures resulted in depression of the forward NADH-ubiquinone oxidoreductase activity of complex I, decreased content of glutathione, and enhancement of the cellular level of H2O2. Depressed transcription of cytosolic Cu/Zn-SOD 1, mitochondrial glutathione peroxidase and catalase was also observed. Activation of the cAMP cascade reversed the depression of the activity of complex I and the accumulation of H2O2. The effect of cAMP involved the cAMP-dependent protein kinase.

Comparison of two enzyme immunometric assays to measure tumor necrosis factor-alpha in human serum

BACKGROUND

Tumor necrosis factor-alpha is a 17.5 kDa, 157 amino acid protein that is a potent lymphoid factor, which exerts cytotoxic effects on a wide range of tumor cells and other target cells. TNF-alpha has been suggested to play a pro-inflammatory role by influencing transendothelial migration of monocytes and elicits the expression of proteolytic enzymes by macrophages and smooth muscle cells within the atherosclerotic plaque.

METHODS

We compared two methods for the quantitative determination of human tumor necrosis factor-alpha in serum samples. Either kit follows the same assay procedure. Serum samples do not need to be diluted before sampling. Standard is provided lyophilized and serial dilutions after reconstitution generate the standard point curves. The tests are enzyme immunometric assays based on a standard 96-well microtiter plate. The wells are coated with anti-human TNF-alpha antibody.

RESULTS

The range of the standard curve is similar in both kits. It spans from 1000 through 15.6 pg/mL. The median TNF-alpha concentration in samples measured by Pierce assay (n=368) was 4.23 pg/mL, (range, 1.34-77.2 pg/mL). A very different median was obtained for the same specimen measured with the Titerzyme EIA (median, 176.96 pg/mL; range, 54.7-283.9 pg/mL; n=364). Substantial significant differences were observed between the two methods.

CONCLUSION

Our results show that the two kits are unmatchable for results they can give when TNF-alpha concentrations are measured in serum samples. One reason of this disagreement could be the matrix effect or a cross-reactivity of one of the two methods. This study shows that the determination of human serum TNF-alpha needs to be standardized, especially when a comparison of results is required.

C-reactive protein and tumor necrosis factor-alpha in gestational hyperglycemia

OBJECTIVES AND STUDY DESIGN

Increasing evidences support an inflammatory origin for gestational hyperglycemia. This paper aims at investigating, cross-sectionally and prospectively, the relationships between tumor necrosis factor-alpha (TNF-alpha) and C-reactive protein (CRP) levels in normoglycemic and hyperglycemic pregnancies of women with and without conventional risk factors for gestational diabetes (GDM).

RESULTS

Both at simple and multiple correlations TNF-alpha levels are associated to fasting insulin, homeostasis model assessment-insulin resistance (HOMA-IR) values and gestational hyperglycemia, while high sensitivity CRP (hsCRP) levels to body mass index (BMI). Furthermore, the TNF-alpha levels of the second trimester and their increments in the third trimester are significant predictors of insulin levels measured at 32-36 weeks in the subgroup of hyperglycemic women with < or = 35 yr, BMI <25 kg/m2 and the absence of a first-degree relative with Type 2 diabetes (respectively, beta=1.1; 95%CI 0.66-1.48; p=0.002 and beta=1.0; 95%CI 0.36-1.66; p=0.02), in a multiple regression model, after multiple adjustments. In a second cohort of women at low risk for GDM (<25 yr, BMI <25 kg/m2 and absence of a first-degree relative with Type 2 diabetes), 24-28 weeks TNF-alpha levels are highly associated with corresponding insulin and HOMA values in the same model (respectively, beta=0.27; 95%CI 0.11-0.43; p=0.001 and beta=0.30; 95%CI 0.14-0.46; p<0.001).

CONCLUSIONS

The data support the developing hypothesis that low-grade systemic inflammation is associated to GDM, in particular for pregnant women without conventional risk factors for gestational hyperglycemia, whose insulin resistance seems less explainable.

Gestational hyperglycemia, zinc, selenium, and antioxidant vitamins

OBJECTIVE

Lower levels of selenium and vitamin E have been described in gestational diabetes, a condition similar to type 2 diabetes, but few data are available about zinc (known to be associated with diabetes) and gestational hyperglycemia. This study evaluated the dietary intake of antioxidant vitamins, zinc, selenium, and serum levels of zinc and selenium in women with gestational hyperglycemia and normoglycemia.

METHODS

A food-frequency questionnaire was administered to 504 pregnant women (210 with hyperglycemia and 294 with normoglycemia). Serum levels of zinc and selenium were analyzed during pregnancy in a second cohort of 71 hyperglycemic and 123 normoglycemic women, with a mean age and body mass index similar to those in the first cohort.

RESULTS

Dietary intakes of zinc and selenium were significantly lower in hyperglycemic patients. In multiple logistic regression analysis, intakes were negatively associated with gestational hyperglycemia (odds ratios of 0.89 for zinc and 0.97 for selenium) after multiple adjustments. There were no significant differences in vitamin intakes. In the second cohort of 194 patients, serum levels of zinc and selenium were significantly lower in patients who had impaired glucose tolerance and negatively associated with gestational hyperglycemia in a multiple logistic regression model (odds ratios of 0.93 for serum zinc and 0.92 for serum selenium).

CONCLUSIONS

Our data suggested a significant inverse association of dietary intakes and serum levels of zinc and selenium with gestational hyperglycemia. If future studies confirm these results, it might be a useful interventional approach to appropriate dietary counseling in order to evaluate the possible decrease in gestational metabolic abnormalities and their adverse consequences.

Mild gestational hyperglycemia, the metabolic syndrome and adverse neonatal outcomes

BACKGROUND

The aim of this study was to evaluate the prevalence of the metabolic syndrome and its effect on neonatal outcomes in pregnancies with different degrees of hyperglycemia.

METHODS

One hundred and fifty women with gestational diabetes, 100 with one abnormal value on the oral glucose tolerance test, 100 with a normal oral glucose challenge test and 350 with an abnormal challenge test and normal tolerance test were enrolled.

RESULTS

The prevalence of the metabolic syndrome was: 0%, 4.9%, 20% and 18% in the normal challenge test, abnormal challenge and normal tolerance test, one abnormal value and gestational diabetes patients, respectively. Offspring birth weights, prevalence of large-for-gestational age babies and icterus were significantly higher in women with an abnormal challenge test (both with a normal tolerance test or one abnormal value or gestational diabetes). Metabolic syndrome was the best predictor of the presence of large-for-gestational age babies in patients with an abnormal challenge and normal tolerance test (OR = 3.15), one abnormal value (OR = 3.53) and gestational diabetes (OR = 4.15).

CONCLUSIONS

Metabolic syndrome in mid-pregnancy was an independent predictor of macrosomia in women with any degree of gestational hyperglycemia; the oral glucose challenge test identifies pregnancies with metabolic abnormalities and adverse neonatal outcomes also in the presence of a normal oral glucose tolerance test.

Obesity or diabetes: what is worse for the mother and for the baby?

OBJECTIVES

The aim of the present study is to evaluate pregnancy outcomes in a cohort of Caucasian pregnant women in relation to their body mass index and glucose tolerance status; the role of central fat distribution, as indicated by waist-to-hip circumference ratio, was also considered.

METHODS

Seven hundred women were studied; they had gestational diabetes or impaired glucose tolerance (250) or normoglycaemia (450). Among them 117 had pre-pregnancy overweight/obesity (44 were obese), 133 hyperglycaemia, but normal weight, and 117 hyperglycaemia and overweight/obesity (42 were obese).

RESULTS

Hypertension, cesarean delivery and prevalence of large-for-gestational age babies were higher in obese (both with normoglycaemia and hyperglycaemia), mainly in those with greater gestational weight gain and central fat distribution (waist-to-hip ratio > 0.90). Normal weight hyperglycaemic women showed better outcomes than obese normoglycaemic women did. In a multiple logistic regression model, obesity (OR=10.6; 95% CI 5.00-22.54) was directly related to hypertension, and independent predictors of cesarean section were: gestational hyperglycaemia (OR=1.78; 95% CI 1.21-2.62), gestational weight gain (OR=1.06; 95% CI 1.02-1.10), and central obesity (OR=1.51; 95% CI 1.02-2.24), while obesity (OR=4.48; 95% CI 2.30-8.71) gestational weight gain (OR=1.08; 95% CI 1.03-1.12) and central fat distribution (OR=1.81: 95% CI 1.12-2.93) were directly related to delivering larger babies, after multiple adjustments.

CONCLUSION

These results suggest that pre-pregnancy obesity and gestational hyperglycaemia were independent risk factors for different adverse pregnancy and neonatal outcomes, while central distribution of fat, and gestational weight gain play an additive adverse role on these outcomes.

Clinical characteristics and outcome of pregnancy in women with gestational hyperglycaemia with and without antibodies to beta-cell antigens

AIMS

To evaluate the prevalence of beta-cell autoantibodies in women with gestational diabetes and impaired glucose tolerance, and identify clinical characteristics differentiating hyperglycaemic patients with and without autoantibodies.

METHODS

One hundred and twenty-three pregnant patients with gestational diabetes, 84 with impaired glucose tolerance and 290 with normoglycaemia were evaluated for anti-islet cell antibodies, glutamic acid decarboxylase (GAD) autoantibodies, and the components of the metabolic syndrome.

RESULTS

Autoantibody positivity was 8.9%, 17.9% and 0.3% in patients with diabetes, impaired tolerance and normoglycaemia, respectively. Hyperglycaemic patients with autoantibodies had lower body mass index, waist, weight gain at the time of the screening test and a lower percentage of previous pregnancies than those without autoantibodies. In addition, their fasting insulin values were significantly lower and inversely related to the presence of autoantibodies (odds ratio (OR) = 0.64; 95% confidence interval (CI) 0.42-0.96), the lowest values being found in anti-GAD+ patients. Autoantibody-positive women with diabetes were more frequently treated with insulin than negative patients (OR = 7.21; 95% CI 1.85-28.08).

CONCLUSIONS

Autoantibody-positive women with gestational hyperglycaemia displayed fewer features of insulin resistance and required more frequent insulin therapy than negative women and presumably had presymptomatic Type 1 diabetes. If this conclusion is corroborated by the follow-up of larger series, clinical and immunological distinction of types of gestational hyperglycaemia would be useful.

Serine (threonine) phosphatase(s) acting on cAMP-dependent phosphoproteins in mammalian mitochondria

Immunochemical and functional evidence showing the existence in the inner membrane and matrix fraction of mammalian mitochondria of serine/threonine phosphatases acting on cAMP-dependent phosphoproteins is presented. Mg(2+)-dependent Ca(2+)-inhibitable PP2C phosphatase, associated to the inner membrane, dephosphorylates the 18 kDa (NDUFS4 gene) of complex I.