The spatial and temporal regulation of the hormonal signal. Role of mitochondria in the formation of a protein complex required for the activation of cholesterol transport and steroids synthesis

Expression of the umami taste receptor T1R1/T1R3 in porcine testis of: Function in regulating testosterone synthesis and autophagy in Leydig cells

Testosterone is a vital male hormone responsible for male sexual characteristics. The taste receptor family 1 subunit 3 (T1R3) regulates testosterone synthesis and autophagy in non-taste cells, and the links with the taste receptor family 1 subunit 1 (T1R1) for umami perception. However, little is known about these mechanisms. Thus, we aimed to determine the relationship between the umami taste receptor (T1R1/T1R3) and testosterone synthesis or autophagy in testicular Leydig cells of the Xiang pig. There was a certain proportion of spermatogenic tubular dysplasia in the Xiang pig at puberty, in which autophagy was enhanced, and the testosterone level was increased with a weak expression of T1R3. Silenced T1R3 decreased testosterone level and intracellular cyclic adenosine monophosphate (cAMP) content and inhibited the messenger RNA (mRNA) expression levels of testosterone synthesis enzyme genes [steroidogenic acute regulatory protein (StAR), hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 1 (3β-HSD1), cytochrome P450 family 17 subfamily A member 1 (CYP17A1) and hydroxysteroid 17-beta dehydrogenase 3 (17β-HSD3)]. In addition, T1R3 increased the number of acidic autophagy bubbles and upregulated the expression levels of autophagy markers [Microtubule-associated protein 1 A/1B-light chain 3 (LC3) and Beclin-1] in testicular Leydig cells of the Xiang pig. Using an umami tasting agonist (10 mM L-glutamate for 6 h), the activation of T1R1/T1R3 enhanced the testosterone synthesis ability by increasing the intracellular cAMP level and upregulated the expression levels of StAR, 3β-HSD1, CYP17A1 and 17β-HSD3 in Leydig cells. Furthermore, the number of acidic autophagy bubbles decreased in the T1R1/T1R3-activated group with the downregulation of the expression levels of the autophagy markers, including LC3 and Beclin-1. These data suggest that the function of T1R1/T1R3 expressed in testicular Leydig cells of the Xiang pig is related to testosterone synthesis and autophagy.

Flavoprotein fluorescence elevation is a marker of mitochondrial oxidative stress in patients with retinal disease

Purpose

Recent studies of glaucoma, age-related macular degeneration, and diabetic retinopathy have demonstrated that flavoprotein fluorescence (FPF) can be utilized non-invasively as an indicator of mitochondrial oxidative stress in the retina. However, a comprehensive assessment of the validity and reliability of FPF in differentiating between healthy and diseased eyes across multiple disease states is lacking. Here, we evaluate the sensitivity and specificity of FPF in discriminating between healthy and diseased eyes in four leading causes of visual impairment worldwide, one of which has not been previously evaluated using FPF. We also evaluate the association between FPF and visual acuity.

Methods

A total of 88 eyes [21 eyes of 21 unaffected controls, 20 eyes from 20 retinal vein occlusion (RVO) patients, 20 eyes from 20 diabetic retinopathy (DR) patients, 17 eyes from 17 chronic exudative age-related macular degeneration (exudative AMD) patients, and 10 eyes from 10 central serous retinopathy (CSR) patients] were included in the present cross-sectional observational study. Eyes were imaged non-invasively using a specially configured fundus camera OcuMet Beacon® (OcuSciences, Ann Arbor, MI). The macula was illuminated using a narrow bandwidth blue light (455 - 470 nm) and fluorescence was recorded using a narrow notch filter to match the peak emission of flavoproteins from 520 to 540 nm. AUROC analysis was used to determine the sensitivity of FPF in discriminating between diseased eyes and healthy eyes. Nonparametric Kruskal-Wallis Tests with post-hoc Mann Whitney U tests with the Holm-Bonferroni correction were performed to assess differences in FPF intensity, FPF heterogeneity, and best corrected visual acuity (BCVA) between the five groups. Spearman rank correlation coefficients were calculated to assess the relationship between FPF and BCVA.

Results

AUROC analysis indicated that FPF intensity is highly sensitive for detecting disease, particularly for exudative AMD subjects (0.989; 95% CI = 0.963 - 1.000, p=3.0 x 107). A significant difference was detected between the FPF intensity, FPF heterogeneity, and BCVA in all four disease states compared to unaffected controls (Kruskal-Wallis Tests, p = 1.06 x 10-8, p = 0.002, p = 5.54 x 10-8, respectively). Compared to healthy controls, FPF intensity values were significantly higher in RVO, DR, exudative AMD, and CSR (p < 0.001, p < 0.001, p < 0.001, and p = 0.001, respectively). Spearman rank correlation coefficient between FPF intensity and BCVA was ρ = 0.595 (p = 9.62 x 10-10).

Conclusions

Despite variations in structural retinal findings, FPF was found to be highly sensitive for detecting retinal disease. Significant FPF elevation were seen in all four disease states, with the exudative AMD patients exhibiting the highest FPF values compared to DR, CSR, and RVO subjects. This is consistent with the hypothesis that there is elevated oxidative stress in all of these conditions as previously demonstrated by blood studies. FPF intensity is moderately correlated with the late-in disease-marker BCVA, which suggests that the degree of FPF elevation can be used as a metabolic indicator of disease severity.

Balancing life and death: BCL-2 family members at diverse ER-mitochondrial contact sites

The outer mitochondrial membrane is a busy place. One essential activity for cellular survival is the regulation of membrane integrity by the BCL-2 family of proteins. Another critical facet of the outer mitochondrial membrane is its close approximation with the endoplasmic reticulum. These mitochondrial-associated membranes (MAMs) occupy a significant fraction of the mitochondrial surface and serve as key signaling hubs for multiple cellular processes. Each of these pathways may be considered as forming their own specialized MAM subtype. Interestingly, like membrane permeabilization, most of these pathways play critical roles in regulating cellular survival and death. Recently, the pro-apoptotic BCL-2 family member BOK has been found within MAMs where it plays important roles in their structure and function. This has led to a greater appreciation that multiple BCL-2 family proteins, which are known to participate in numerous functions throughout the cell, also have roles within MAMs. In this review, we evaluate several MAM subsets, their role in cellular homeostasis, and the contribution of BCL-2 family members to their functions.

Angiotensin II Regulates Mitochondrial mTOR Pathway Activity Dependent on Acyl-CoA Synthetase 4 in Adrenocortical Cells

Two well-known protein complexes in mammalian cells, mTOR type 1 and type 2 (mTORC1/2) are involved in several cellular processes such as protein synthesis, cell proliferation, and commonly dysregulated in cancer. An acyl-CoA synthetase type 4 (ACSL4) is one of the most recently mTORC1/2 regulators described, in breast cancer cells. The expression of ACSL4 is hormone-regulated in adrenocortical cells and required for steroid biosynthesis. mTORC1/2 have been reported to be crucial in the proliferation of human adrenocortical tumor cells H295R and interestingly reported at several subcellular locations, which has brought cell biology to the vanguard of the mTOR signaling field. In the present work, we study the regulation of mTORC1/2 activation by angiotensin II (Ang II)-the trophic hormone for adrenocortical cells-the subcellular localization of mTORC1/2 signaling proteins and the role of ACSL4 in the regulation of this pathway, in H295R cells. Ang II promotes activation by phosphorylation of mTORC1/2 pathway proteins in a time-dependent manner. Mitochondrial pools of ribosomal protein S6, protein kinase B (Akt) in threonine 308, and serine 473 and Rictor are phosphorylated and activated. Glycogen synthase kinase type 3 (GSK3) is phosphorylated and inactivated in mitochondria, favoring mTORC1 activation. Epidermal growth factor, a classic mTORC1/2 activator, promoted unique activation kinetics of mTORC1/2 pathway, except for Akt phosphorylation. Here, we demonstrate that ACSL4 is necessary for mTORC1/2 effectors phosphorylation and H295R proliferation, triggered by Ang II. Ang II promotes activation of mitochondrial mTORC1/2 signaling proteins, through ACSL4, with a direct effect on adrenocortical cellular proliferation.

Molecular Dysfunctions of Mitochondria-Associated Endoplasmic Reticulum Contacts in Atherosclerosis

Atherosclerosis is a chronic lipid-driven inflammatory disease that results in the formation of lipid-rich and immune cell-rich plaques in the arterial wall, which has high morbidity and mortality in the world. The mechanism of atherosclerosis is still unclear now. Potential hypotheses involved in atherosclerosis are chronic inflammation theory, lipid percolation theory, mononuclear-macrophage theory, endothelial cell (EC) injury theory, and smooth muscle cell (SMC) mutation theory. Changes of phospholipids, glucose, critical proteins, etc. on mitochondria-associated endoplasmic reticulum membrane (MAM) can cause the progress of atherosclerosis. This review describes the structural and functional interaction between mitochondria and endoplasmic reticulum (ER) and explains the role of critical molecules in the structure of MAM during atherosclerosis.

Aging-Related Increase of cGMP Disrupts Mitochondrial Homeostasis in Leydig Cells

Since mitochondria play an essential role in the testosterone biosynthesis, serve as power centers and are a source of oxidative stress, a possible mitochondrial dysfunction could be connected with decreased activity of Leydig cells and lowered testosterone production during aging. Here we chronologically analyzed age-related alterations of mitochondrial function in Leydig cells correlated by the progressive rise of cGMP signaling and with respect to testosterone synthesis. To target cGMP signaling in Leydig cells, acute or long-term in vivo or ex vivo treatments with sildenafil (phosphodiesterase 5 [PDE5] inhibitor) were performed. Aging-related accumulation of cGMP in the Leydig cells is associated with mitochondrial dysfunction illustrated by reduced ATP and steroid production, lowered O2 consumption, increased mitochondrial abundance and mtDNA copies number, decreased expression of genes that regulate mitochondrial biogenesis (Ppargc1a/PGC1a-Tfam-Nrf1/NRF1), mitophagy (Pink1), fusion (Mfn1, Opa1), and increased Nrf2/NRF2. Acute in vivo PDE5 inhibition overaccumulated cGMP and stimulated testosterone but reduced ATP production in Leydig cells from adult, middle-aged, and old rats. The increased ATP/O ratio observed in cells from old compared to adult rats was diminished after stimulation of cGMP signaling. Opposite, long-term PDE5 inhibition decreased cGMP signaling and improved mitochondrial function/dynamics in Leydig cells from old rats. Mitochondrial abundance in Leydig cells decreased while ATP levels increased. Chronic treatment elevated Tfam, Nrf1, Nrf2, Opa1, Mfn1, Drp1, and normalized Pink1 expression. Altogether, long-term PDE5 inhibition prevented age-related NO and cGMP elevation, improved mitochondrial dynamics/function, and testosterone production. The results pointed on cGMP signaling in Leydig cells as a target for pharmacological manipulation of aging-associated changes in mitochondrial function and testosterone production.

Longitudinal Expression of Testicular TAS1R3 from Prepuberty to Sexual Maturity in Congjiang Xiang Pigs

Simple Summary

Taste receptor type 1 subunit 3 (T1R3), a sweet/umami taste receptor, is widely expressed from the tongue to the testis, and testis expression is associated with male sterility. In Congjiang Xiang pigs, T1R3 is expressed in elongating/elongated spermatids and Leydig cells in a stage-dependent manner during postnatal development and the spermatogenic cycle. T1R3 may contribute to regulation of spermatid differentiation and Leydig cell function, and may therefore help limit the incidence of various male reproductive pathologies.

Abstract

Testicular expression of taste receptor type 1 subunit 3 (T1R3), a sweet/umami taste receptor, has been implicated in spermatogenesis and steroidogenesis in mice. We explored the role of testicular T1R3 in porcine postnatal development using the Congjiang Xiang pig, a rare Chinese miniature pig breed. Based on testicular weights, morphology, and testosterone levels, four key developmental stages were identified in the pig at postnatal days 15–180 (prepuberty: 30 day; early puberty: 60 day; late puberty: 90 day; sexual maturity: 120 day). During development, testicular T1R3 exhibited stage-dependent and cell-specific expression patterns. In particular, T1R3 levels increased significantly from prepuberty to puberty (p < 0.05), and expression remained high until sexual maturity (p < 0.05), similar to results for phospholipase Cβ2 (PLCβ2). The strong expressions of T1R3/PLCβ2 were observed at the cytoplasm of elongating/elongated spermatids and Leydig cells. In the eight-stage cycle of the seminiferous epithelium in pigs, T1R3/PLCβ2 levels were higher in the spermatogenic epithelium at stages II–VI than at the other stages, and the strong expressions were detected in elongating/elongated spermatids and residual bodies. The message RNA (mRNA) levels of taste receptor type 1 subunit 1 (T1R1) in the testis showed a similar trend to levels of T1R3. These data indicate a possible role of T1R3 in the regulation of spermatid differentiation and Leydig cell function.

Mitochondria-Associated Endoplasmic Reticulum Membranes in Breast Cancer

Mitochondria-associated ER membranes (MAMs) represent a crucial intracellular signaling hub, that regulates various cellular events including Ca²⁺ homeostasis, lipid metabolism, mitochondrial function, and cellular survival and death. All of these MAM-mediated cellular events contribute to carcinogenesis. Indeed, altered functions of MAMs in several types of cancers have been documented, in particular for breast cancer. Over the past years, altered expression of many MAM-resident proteins have been reported in breast cancer. These MAM-resident proteins play an important role in regulation of breast cancer initiation and progression. In the current review, we discuss our current knowledge about the functions of MAMs, and address the underlying mechanisms through which MAM-resident proteins regulate breast cancer. A fuller understanding of the pathways through which MAMs regulate breast cancer, and identification of breast cancer-specific MAM-resident proteins may help to develop novel therapeutic strategies for breast cancer.

Hypoxia-mediated inhibition of cholesterol synthesis leads to disruption of nocturnal sex steroidogenesis in the gonad of koi carp, Cyprinus carpio

Reproductively mature koi carps (Cyprinus carpio) showed a prominent diurnal variation of sex steroids with sustained nocturnal rise. Exposure to chronic hypoxia (DO < 0.8 mg/l) disrupted nocturnal sex steroid production in koi carp gonads. Inhibition of sex steroidogenesis is linked to the down-regulation of HMG-Co A reductase (p < 0.05), which acts as a rate-limiting enzyme in the mevalonate pathway for cholesterol production. HMG-CoA reductase inhibition was obvious in the gonads and liver of both sexes during 18.00 h and 21.00 h resulting in hypocholesterolemia (p < 0.05). The levels of sex steroids, such as estradiol, testosterone, and 11-keto-testosterone in gonads were depleted below the optimum levels owing to disruption of de novo cholesterol synthesis along with attenuation of HDL-cholesterol level in serum. Inhibition of melatonin under hypoxic conditions indicates disruption of melatonin effects on the hypothalamus-pituitary-gonadal (HPG) axis of koi carp. Under severe hypoxic stress, koi carp promoted energy conservation by switching over to the triglyceride (TGA) pathway instead of the mevalonate pathway to suppress cholesterol production. Chronic hypoxia inhibited cholesterol synthesis, a prerequisite for gonadal maturation. It promoted TGA production, as an alternative energy source, suggesting a probable mitigation strategy adopted by hypoxia-tolerant fish to deal with low dissolved oxygen frequently occurring in aquatic bodies.

Insulin/IGF1 signaling regulates the mitochondrial biogenesis markers in steroidogenic cells of prepubertal testis, but not ovary

Controlled changes in mitochondrial biogenesis and morphology are required for cell survival and homeostasis, but the molecular mechanisms are largely unknown. Here, male and female prepubertal mice (P21) with insulin and IGF1 receptors deletions in steroidogenic tissues (Insr/Igf1r-DKO) were used to investigate transcription of the key regulators of mitochondrial biogenesis (Ppargc1a, Ppargc1b, Pparg, Nrf1, Tfam) and architecture in Leydig cells, ovaries, and adrenals. Results showed that the expression of PGC1, a master regulator of mitochondrial biogenesis and integrator of environmental signals, and its downstream target Tfam, significantly decreased in androgen-producing Leydig cells. This is followed by reduction of Mtnd1, a mitochondrial DNA encoded transcript whose core subunit belongs to the minimal assembly required for catalysis. The same markers remained unchanged in ovaries. In contrast, in adrenals, the pattern of transcripts for mitochondrial biogenesis markers was the same in both sexes, but opposite from that observed in Leydig cells. The level of transcripts for markers of mitochondrial architecture (Mfn1, Mfn2) significantly increased in Leydig cells from Insr/Igf1r-DKO, but not in ovaries. This was followed by mitochondrial morphology disturbance, suggesting that the mitochondrial phase of steroidogenesis could be affected. Indeed, basal and pregnenolone stimulated progesterone productions in the mitochondria of Leydig cells from Insr/Igf1r-DKO decreased more than androgen production, and were barely detectable. Our results are the first to show that INSR/IGF1R are important for mitochondrial biogenesis in gonadal steroidogenic cells of prepubertal males, but not females and they serve as important regulators of mitochondrial architecture and biogenesis markers in Leydig cells.

Angiotensin II stimulation promotes mitochondrial fusion as a novel mechanism involved in protein kinase compartmentalization and cholesterol transport in human adrenocortical cells

In steroid-producing cells, cholesterol transport from the outer to the inner mitochondrial membrane is the first and rate-limiting step for the synthesis of all steroid hormones. Cholesterol can be transported into mitochondria by specific mitochondrial protein carriers like the steroidogenic acute regulatory protein (StAR). StAR is phosphorylated by mitochondrial ERK in a cAMP-dependent transduction pathway to achieve maximal steroid production. Mitochondria are highly dynamic organelles that undergo replication, mitophagy and morphology changes, all processes allowed by mitochondrial fusion and fission, known as mitochondrial dynamics. Mitofusin (Mfn) 1 and 2 are GTPases involved in the regulation of fusion, while dynamin-related protein 1 (Drp1) is the major regulator of mitochondrial fission. Despite the role of mitochondrial dynamics in neurological and endocrine disorders, little is known about fusion/fission in steroidogenic tissues. In this context, the present work aimed to study the role of angiotensin II (Ang II) in protein subcellular compartmentalization, mitochondrial dynamics and the involvement of this process in the regulation of aldosterone synthesis. We demonstrate here that Ang II stimulation promoted the recruitment and activation of PKCε, ERK and its upstream kinase MEK to the mitochondria, all of them essential for steroid synthesis. Moreover, Ang II prompted a shift from punctate to tubular/elongated (fusion) mitochondrial shape, in line with the observation of hormone-dependent upregulation of Mfn2 levels. Concomitantly, mitochondrial Drp1 was diminished, driving mitochondria toward fusion. Moreover, Mfn2 expression is required for StAR, ERK and MEK mitochondrial localization and ultimately for aldosterone synthesis. Collectively, this study provides fresh insights into the importance of hormonal regulation in mitochondrial dynamics as a novel mechanism involved in aldosterone production.

Aspectos generales del transporte de colesterol en la esteroidogénesis de la placenta humana

La placenta humana requiere de colesterol para sintetizar la progesterona que mantiene la relación entre el feto y la madre, lo que le permite concluir de manera exitosa el embarazo. La placenta incorpora el colesterol principalmente a través de las lipoproteínas de baja densidad (LDL) que se obtienen del torrente circulatorio materno por un mecanismo de endocitosis. A los endosomas que se generan en este proceso se les unen varias proteínas conformando los endosomas tardíos, que degradan las LDL y liberan el colesterol a las mitocondrias del sinciciotrofoblasto que lo transforman en pregnenolona y posteriormente en progesterona. Las proteínas de fusión de membranas denominados complejos SNARE participan en la liberación del colesterol en sitios de contacto específicos en donde se localizan las proteínas mitocondriales responsables de la esteroidogénesis.

ER-mitochondria interactions: Both strength and weakness within cancer cells

ER-mitochondria contact sites represent hubs for signaling that control mitochondrial biology related to several aspects of cellular survival, metabolism, cell death sensitivity and metastasis, which all contribute to tumorigenesis. Altered ER-mitochondria contacts can deregulate Ca²⁺ homeostasis, phospholipid metabolism, mitochondrial morphology and dynamics. MAM represent both a hot spot in cancer onset and progression and an Achilles' heel of cancer cells that can be exploited for therapeutic perspectives. Over the past years, an increasing number of cancer-related proteins, including oncogenes and tumor suppressors, have been localized in MAM and exert their pro- or antiapoptotic functions through the regulation of Ca²⁺ transfer and signaling between the two organelles. In this review, we highlight the central role of ER-mitochondria contact sites in tumorigenesis and focus on chemotherapeutic drugs or potential targets that act on MAM properties for new therapeutic approaches in cancer.

Function of CYP11A1 in the mitochondria

Steroids are synthesized from the adrenal glands and gonads by enzymes of the cytochromes P450 and hydroxysteroid dehydrogenase in nature. These enzymes are located in the membrane of endoplasmic reticulum and mitochondria to catalyze redox reactions using electrons transported from the membrane. In the mitochondria, steroidogenic enzymes are inserted into the inner membrane with the bulk of the protein facing the matrix. They are not only important for steroid biosynthesis, their presence also affects mitochondrial morphology. Mitochondria undergo constant fission and fusion; they play important roles in energy production, apoptosis, and metabolism. Their defects often lead to human diseases. Mitochondrial cristae are usually lamellar in shape, but can also assume different shapes. Cristae in the mitochondria of steroidogenic cells are tubular-vesicular in shape. This cristae shape is also related to the degree of steroidogenic cell differentiation. Steroidogenic enzymes in the mitochondria appear to have a dual role in shaping the morphology of mitochondria and in steroid production.

The ER-mitochondria couple: In life and death from steroidogenesis to tumorigenesis

Steroidogenesis is a multistep process where interorganelle communications between the endoplasmic reticulum and mitochondria are critical. These intimate interactions physically occur through the Mitochondria-Associated ER membranes called MAMs. MAMs play important roles in mitochondrial morphology and in many cellular functions ranging from lipid metabolism, to calcium signaling and apoptosis together with a critical effect on steroidogenesis. Moreover, our recent characterization of new MAM resident proteins in adrenocortical cells extends the function of MAM in the mechanism of resistance of cancer cells to apoptotic stimuli and offers new perspectives in targeted therapeutic approaches for adrenocortical tumorigenesis.

Role of Protein Phosphorylation and Tyrosine Phosphatases in the Adrenal Regulation of Steroid Synthesis and Mitochondrial Function

In adrenocortical cells, adrenocorticotropin (ACTH) promotes the activation of several protein kinases. The action of these kinases is linked to steroid production, mainly through steroidogenic acute regulatory protein (StAR), whose expression and activity are dependent on protein phosphorylation events at genomic and non-genomic levels. Hormone-dependent mitochondrial dynamics and cell proliferation are functions also associated with protein kinases. On the other hand, protein tyrosine dephosphorylation is an additional component of the ACTH signaling pathway, which involves the "classical" protein tyrosine phosphatases (PTPs), such as Src homology domain (SH) 2-containing PTP (SHP2c), and members of the MAP kinase phosphatase (MKP) family, such as MKP-1. PTPs are rapidly activated by posttranslational mechanisms and participate in hormone-stimulated steroid production. In this process, the SHP2 tyrosine phosphatase plays a crucial role in a mechanism that includes an acyl-CoA synthetase-4 (Acsl4), arachidonic acid (AA) release and StAR induction. In contrast, MKPs in steroidogenic cells have a role in the turn-off of the hormonal signal in ERK-dependent processes such as steroid synthesis and, perhaps, cell proliferation. This review analyzes the participation of these tyrosine phosphates in the ACTH signaling pathway and the action of kinases and phosphatases in the regulation of mitochondrial dynamics and steroid production. In addition, the participation of kinases and phosphatases in the signal cascade triggered by different stimuli in other steroidogenic tissues is also compared to adrenocortical cell/ACTH and discussed.

Role of the steroidogenic acute regulatory protein in health and disease

Steroid hormones are an important class of regulatory molecules that are synthesized in steroidogenic cells of the adrenal, ovary, testis, placenta, brain, and skin, and influence a spectrum of developmental and physiological processes. The steroidogenic acute regulatory protein (STAR) predominantly mediates the rate-limiting step in steroid biosynthesis, i.e., the transport of the substrate of all steroid hormones, cholesterol, from the outer to the inner mitochondrial membrane. At the inner membrane, cytochrome P450 cholesterol side chain cleavage enzyme cleaves the cholesterol side chain to form the first steroid, pregnenolone, which is converted by a series of enzymes to various steroid hormones in specific tissues. Both basic and clinical evidence have demonstrated the crucial involvement of the STAR protein in the regulation of steroid biosynthesis. Multiple levels of regulation impinge on STAR action. Recent findings demonstrate that hormone-sensitive lipase, through its action on the hydrolysis of cholesteryl esters, plays an important role in regulating STAR expression and steroidogenesis which involve the liver X receptor pathway. Activation of the latter influences macrophage cholesterol efflux that is a key process in the prevention of atherosclerotic cardiovascular disease. Appropriate regulation of steroid hormones is vital for proper functioning of many important biological activities, which are also paramount for geriatric populations to live longer and healthier. This review summarizes the current level of understanding on tissue-specific and hormone-induced regulation of STAR expression and steroidogenesis, and provides insights into a number of cholesterol and/or steroid coupled physiological and pathophysiological consequences.

Mitochondrial Redox Dysfunction and Environmental Exposures

SIGNIFICANCE

Mitochondria are structurally and biochemically diverse, even within a single type of cell. Protein complexes localized to the inner mitochondrial membrane synthesize ATP by coupling electron transport and oxidative phosphorylation. The organelles produce reactive oxygen species (ROS) from mitochondrial oxygen and ROS can, in turn, alter the function and expression of proteins used for aerobic respiration by post-translational and transcriptional regulation.

RECENT ADVANCES

New interest is emerging not only into the roles of mitochondria in disease development and progression but also as a target for environmental toxicants.

CRITICAL ISSUES

Dysregulation of respiration has been linked to cell death and is a major contributor to acute neuronal trauma, peripheral diseases, as well as chronic neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease.

FUTURE DIRECTIONS

Here, we discuss the mechanisms underlying the sensitivity of the mitochondrial respiratory complexes to redox modulation, as well as examine the effects of environmental contaminants that have well-characterized mitochondrial toxicity. The contaminants discussed in this review are some of the most prevalent and potent environmental contaminants that have been linked to neurological dysfunction, altered cellular respiration, and oxidation.

The role of mitochondrial fusion and StAR phosphorylation in the regulation of StAR activity and steroidogenesis

The steroidogenic acute regulatory (StAR) protein regulates the rate-limiting step in steroidogenesis, i.e. the delivery of cholesterol from the outer (OMM) to the inner (IMM) mitochondrial membrane. StAR is a 37-kDa protein with an N-terminal mitochondrial targeting sequence that is cleaved off during mitochondrial import to yield 30-kDa intramitochondrial StAR. StAR acts exclusively on the OMM and its activity is proportional to how long it remains on the OMM. However, the precise fashion and the molecular mechanism in which StAR remains on the OMM have not been elucidated yet. In this work we will discuss the role of mitochondrial fusion and StAR phosphorylation by the extracellular signal-regulated kinases 1/2 (ERK1/2) as part of the mechanism that regulates StAR retention on the OMM and activity.

Stress triggers mitochondrial biogenesis to preserve steroidogenesis in Leydig cells

Adaptability to stress is a fundamental prerequisite for survival. Mitochondria are a key component of the stress response in all cells. For steroid-hormones-producing cells, including also Leydig cells of testes, the mitochondria are a key control point for the steroid biosynthesis and regulation. However, the mitochondrial biogenesis in steroidogenic cells has never been explored. Here we show that increased mitochondrial biogenesis is the adaptive response of testosterone-producing Leydig cells from stressed rats. All markers of mitochondrial biogenesis together with transcription factors and related kinases are up-regulated in Leydig cells from rats exposed to repeated psychophysical stress. This is followed with increased mitochondrial mass. The expression of PGC1, master regulator of mitochondrial biogenesis and integrator of environmental signals, is stimulated by cAMP-PRKA, cGMP, and β-adrenergic receptors. Accordingly, stress-triggered mitochondrial biogenesis represents an adaptive mechanism and does not only correlate with but also is an essential for testosterone production, being both events depend on the same regulators. Here we propose that all events induced by acute stress, the most common stress in human society, provoke adaptive response of testosterone-producing Leydig cells and activate PGC1, a protein required to make new mitochondria but also protector against the oxidative damage. Given the importance of mitochondria for steroid hormones production and stress response, as well as the role of steroid hormones in stress response and metabolic syndrome, we anticipate our result to be a starting point for more investigations since stress is a constant factor in life and has become one of the most significant health problems in modern societies.

Structure-to-function relationships of bacterial translocator protein (TSPO): a focus on Pseudomonas

The translocator protein (TSPO), which was previously designated as the peripheral-type benzodiazepine receptor, is a 3.5 billion year-old evolutionarily conserved protein expressed by most Eukarya, Archae and Bacteria, but its organization and functions differ remarkably. By taking advantage of the genomic data available on TSPO, we focused on bacterial TSPO and attempted to define functions of TSPO in Pseudomonas via in silico approaches. A tspo ortholog has been identified in several fluorescent Pseudomonas. This protein presents putative binding motifs for cholesterol and PK 11195, which is a specific drug ligand of mitochondrial TSPO. While it is a common surface distribution, the sense of insertion and membrane localization differ between α- and γ-proteobacteria. Experimental published data and STRING analysis of common TSPO partners in fluorescent Pseudomonas indicate a potential role of TSPO in the oxidative stress response, iron homeostasis and virulence expression. In these bacteria, TSPO could also take part in signal transduction and in the preservation of membrane integrity.