Bi-allelic LETM1 variants perturb mitochondrial ion homeostasis leading to a clinical spectrum with predominant nervous system involvement

Leucine zipper-EF-hand containing transmembrane protein 1 (LETM1) encodes an inner mitochondrial membrane protein with an osmoregulatory function controlling mitochondrial volume and ion homeostasis. The putative association of LETM1 with a human disease was initially suggested in Wolf-Hirschhorn syndrome, a disorder that results from de novo monoallelic deletion of chromosome 4p16.3, a region encompassing LETM1. Utilizing exome sequencing and international gene-matching efforts, we have identified 18 affected individuals from 11 unrelated families harboring ultra-rare bi-allelic missense and loss-of-function LETM1 variants and clinical presentations highly suggestive of mitochondrial disease. These manifested as a spectrum of predominantly infantile-onset (14/18, 78%) and variably progressive neurological, metabolic, and dysmorphic symptoms, plus multiple organ dysfunction associated with neurodegeneration. The common features included respiratory chain complex deficiencies (100%), global developmental delay (94%), optic atrophy (83%), sensorineural hearing loss (78%), and cerebellar ataxia (78%) followed by epilepsy (67%), spasticity (53%), and myopathy (50%). Other features included bilateral cataracts (42%), cardiomyopathy (36%), and diabetes (27%). To better understand the pathogenic mechanism of the identified LETM1 variants, we performed biochemical and morphological studies on mitochondrial K+/H+ exchange activity, proteins, and shape in proband-derived fibroblasts and muscles and in Saccharomyces cerevisiae, which is an important model organism for mitochondrial osmotic regulation. Our results demonstrate that bi-allelic LETM1 variants are associated with defective mitochondrial K+ efflux, swollen mitochondrial matrix structures, and loss of important mitochondrial oxidative phosphorylation protein components, thus highlighting the implication of perturbed mitochondrial osmoregulation caused by LETM1 variants in neurological and mitochondrial pathologies.

Variant Selection and Interpretation: An Example of Modified VarSome Classifier of ACMG Guidelines in the Diagnostic Setting

Variant interpretation is challenging as it involves combining different levels of evidence in order to evaluate the role of a specific variant in the context of a patient's disease. Many in-depth refinements followed the original 2015 American College of Medical Genetics (ACMG) guidelines to overcome subjective interpretation of criteria and classification inconsistencies. Here, we developed an ACMG-based classifier that retrieves information for variant interpretation from the VarSome Stable-API environment and allows molecular geneticists involved in clinical reporting to introduce the necessary changes to criterion strength and to add or exclude criteria assigned automatically, ultimately leading to the final variant classification. We also developed a modified ACMG checklist to assist molecular geneticists in adjusting criterion strength and in adding literature-retrieved or patient-specific information, when available. The proposed classifier is an example of integration of automation and human expertise in variant curation, while maintaining the laboratory analytical workflow and the established bioinformatics pipeline.

Molecular Epidemiology in 591 Italian Probands With Nonsyndromic Retinitis Pigmentosa and Usher Syndrome

Purpose

To describe the molecular epidemiology of nonsyndromic retinitis pigmentosa (RP) and Usher syndrome (US) in Italian patients.

Methods

A total of 591 probands (315 with family history and 276 sporadics) were analyzed. For 155 of them, we performed a family segregation study, considering a total of 382 relatives. Probands were analyzed by a customized multigene panel approach. Sanger sequencing was used to validate all genetic variants and to perform family segregation studies. Copy number variants of selected genes were analyzed by multiplex ligation-dependent probe amplification. Four patients who tested negative to targeted next-generation sequencing analysis underwent clinical exome sequencing.

Results

The mean diagnostic yield of molecular testing among patients with a family history of retinal disorders was 55.2% while the diagnostic yield including sporadic cases was 37.4%. We found 468 potentially pathogenic variants, 147 of which were unpublished, in 308 probands and 66 relatives. Mean ages of onset of the different classes of RP were autosomal dominant RP, 19.3 ± 12.6 years; autosomal recessive RP, 23.2 ± 16.6 years; X-linked RP, 13.9 ± 9.9 years; and Usher syndrome, 18.9 ± 9.5 years. We reported potential new genotype-phenotype correlations in three probands, two revealed by TruSight One testing. All three probands showed isolated RP caused by biallelic variants in genes usually associated with syndromes such as PERCHING and Senior-Loken or with retinal dystrophy, iris coloboma, and comedogenic acne syndrome.

Conclusions

This is the largest molecular study of Italian patients with RP in the literature, thus reflecting the epidemiology of the disease in Italy with reasonable accuracy.

Genetic test for the prescription of diets in support of physical activity

Owing to the fields of nutrigenetics and nutrigenomics today we can think of devising approaches to optimize health, delay onset of diseases and reduce its severity according to our genetic blue print. However this requires a deep understanding of nutritional impact on expression of genes that may result in a specific phenotype. The extensive research and observational studies during last two decades reporting interactions between genes, diet and physical activity suggest a cross talk between various genetic and environmental factors and lifestyle interventions. Although considerable efforts have been made in unraveling the mechanisms of gene-diet interactions the scientific evidences behind developing commercial genetic tests for providing personalized nutrition recommendations are still scarce. In this scenario the current mini-review aims to provide useful insights into salient feature of nutrition based genetic research and its commercial application and the ethical issue and concerns related to its outcome.

Somatic Variant Analysis Identifies Targets for Tailored Therapies in Patients with Vascular Malformations

Vascular malformations include various disorders characterized by morphological, structural and/or functional alterations of blood and lymph vessels. Most are sporadic, due to somatic mutations. Here, we report a cohort of patients with sporadic and/or unifocal vascular malformations, in whom we carried out next generation sequencing analysis of a panel of genes associated with vascular malformations. The 115 patients analyzed were from different clinical centres. In 37 patients (32%), we found pathogenic mutations: most of these were gain-of-function mutations in PIK3CA (18%, 21/115) and TEK (13/115, 11%). We also found mutations in GNAQ, CCM2 and PTEN. Identifying pathogenic variants in patients with vascular malformations can help improve management, particularly in cases with activating mutations that cause an increase in cell proliferation. Personalized pharmacological treatment, if possible, is now considered preferable to surgery and can help prevent recurrences, i.e., long-term complications of residual malformation or regrowth of tumors. For instance, rapamycin is currently being investigated for the treatment of various vascular malformations associated with hyperactivation of the phosphoinositide 3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway.

Analysis of machine learning algorithms as integrative tools for validation of next generation sequencing data

OBJECTIVE

While next generation sequencing (NGS) has become the technology of choice for clinical diagnostics, most genetic laboratories still use Sanger sequencing for orthogonal confirmation of NGS results. Previous studies have shown that when the quality of NGS data is high, most calls are indicated by Sanger sequencing, making confirmation redundant. We aimed at establishing a set of criteria that make it possible to distinguish NGS calls that need orthogonal confirmation from those that do not would significantly decrease the amount of work necessary to reach a diagnosis.

MATERIALS AND METHODS

A data set of 7976 NGS calls confirmed as true or false positive by Sanger sequencing was used to train and test different machine learning (ML) approaches. By varying the size and class balance of the training dataset, we measured the performance of the different algorithms to determine the conditions under which ML is a valid approach for confirming NGS calls in a diagnostic environment.

RESULTS

Our results indicate that machine learning is a valid approach to find variant calls that need more investigation, but in order to reach the high accuracy required in a clinical environment, the training data set must include enough observations and these observations must be well-balanced between true/false positive NGS calls.

CONCLUSIONS

Our results show that it is possible to integrate the diagnostic NGS validation workflow with a machine learning approach to reduce the number of Sanger confirmations of high- quality NGS calls, reducing the time and costs of diagnosis.

ICH3, a selective alpha7 nicotinic acetylcholine receptor agonist, modulates adipocyte inflammation associated with obesity

PURPOSE

The alpha7 nicotinic acetylcholine receptor (α7nAChR), involved in the modulation of inflammation and insulin sensitivity, is downregulated in white adipose tissue (WAT) of obese patients. This study aims to test the ability of a selective synthetic α7nAChR agonist, the spirocyclic Δ²-isoxazoline derivative (R)-(-)-ICH3 (ICH3), to counteract acute inflammation and obesity-associated modifications in WAT.

METHODS

We employed the LPS-septic shock murine model, human primary adipocytes and diet-induced obese (DIO) mice. Inflammatory factor expression was assessed by ELISA and quantitative real-time PCR. Flow cytometry was employed to define WAT inflammatory infiltrate. Insulin signaling was monitored by quantification of AKT phosphorylation.

RESULTS

In the septic shock model, ICH3 revealed antipyretic action and reduced the surge of circulating cytokines. In vitro, ICH3 stimulation (10 µM) preserved viability of human adipocytes, decreased IL-6 mRNA (P < 0.05) and blunted LPS-induced peak of TNFα (P < 0.05) and IL-6 (P < 0.01). Chronic administration of ICH3 to DIO mice was associated with lower numbers of CD8+ T cells (P < 0.05) and to changed WAT expression of inflammatory factors (Hp, P < 0.05; CD301/MGL1, P < 0.01; Arg-1, P < 0.05). As compared to untreated, ICH3 DIO mice exhibited improved insulin signaling in the skeletal muscle (P < 0.01) mirrored by an improved response to glucose load (ipGTT: P < 0.05 at 120 min).

CONCLUSIONS

We proved that ICH3 is an anti-inflammatory drug, able to reduce inflammatory cytokines in human adipocytes and to blunt the effects of obesity on WAT inflammatory profile, on glucose tolerance and on tissue insulin sensitivity.

Transcriptomic Analysis of Single Isolated Myofibers Identifies miR-27a-3p and miR-142-3p as Regulators of Metabolism in Skeletal Muscle

Skeletal muscle is composed of different myofiber types that preferentially use glucose or lipids for ATP production. How fuel preference is regulated in these post-mitotic cells is largely unknown, making this issue a key question in the fields of muscle and whole-body metabolism. Here, we show that microRNAs (miRNAs) play a role in defining myofiber metabolic profiles. mRNA and miRNA signatures of all myofiber types obtained at the single-cell level unveiled fiber-specific regulatory networks and identified two master miRNAs that coordinately control myofiber fuel preference and mitochondrial morphology. Our work provides a complete and integrated mouse myofiber type-specific catalog of gene and miRNA expression and establishes miR-27a-3p and miR-142-3p as regulators of lipid use in skeletal muscle.

CRB1-Related Cystic Maculopathy in Twins Conceived Through Heterologous Fertilization With Variant-Carrying Oocytes

Cystic maculopathy has been associated with genetic disorders such as retinitis pigmentosa, X-linked retinoschisis, cone dystrophy, and foveal retinoschisis. Familial foveal retinoschisis was recently described as a rare disease caused by CRB1 variants. The authors report the phenotype-genotype pattern of a pair of dizygotic twins with early-onset cystic maculopathy due to CRB1 pathogenic variants. The twins were conceived by heterologous fertilization with variant-carrying oocytes. The probands were monitored for a period of 4 years. Next generation sequencing of a panel of genes responsible for retinal dystrophies was performed. Both children carried three pathogenic variants in CRB1: a novel heterozygous truncating variant p.(Val855*) inherited from the father and two known heterozygous missense variants, p.[(Phe144Val; Thr745Met)], inherited from the oocyte donor. The findings confirm that CRB1 variants can be responsible for foveal retinoschisis with variable clinical expressivity ranging from schitic macular alteration to early-onset forms of cystic maculopathy. The authors highlight the importance of exome analysis of gamete donors to assess the likelihood of recessively inherited disorders by means of a prediction algorithm able to combine parent and donor exome data. [J Pediatr Ophthalmol Strabismus. 2020;57:e19-e24.].

Male Infertility Diagnosis: Improvement of Genetic Analysis Performance by the Introduction of Pre-Diagnostic Genes in a Next-Generation Sequencing Custom-Made Panel

BACKGROUND

Infertility affects about 7% of the general male population. The underlying cause of male infertility is undefined in about 50% of cases (idiopathic infertility). The number of genes involved in human spermatogenesis is over two thousand. Therefore, it is essential to analyze a large number of genes that may be involved in male infertility. This study aimed to test idiopathic male infertile patients negative for a validated panel of "diagnostic" genes, for a wide panel of genes that we have defined as "pre-diagnostic."

METHODS

We developed a next-generation sequencing (NGS) gene panel including 65 pre-diagnostic genes that were used in 12 patients who were negative to a diagnostic genetic test for male infertility disorders, including primary spermatogenic failure and central hypogonadism, consisting of 110 genes.

RESULTS

After NGS sequencing, variants in pre-diagnostic genes were identified in 10/12 patients who were negative to a diagnostic test for primary spermatogenic failure (n = 9) or central hypogonadism (n = 1) due to mutations of single genes. Two pathogenic variants of DNAH5 and CFTR genes and three uncertain significance variants of DNAI1, DNAH11, and CCDC40 genes were found. Moreover, three variants with high impact were found in AMELY, CATSPER 2, and ADCY10 genes.

CONCLUSION

This study suggests that searching for pre-diagnostic genes may be of relevance to find the cause of infertility in patients with apparently idiopathic primary spermatogenic failure due to mutations of single genes and central hypogonadism.

Monogenic hypertension

Hypertension is a significant public health problem. Thirty percent of cases are caused by a single genetic mutation. Hypertension is the predominant and usually the only manifestation in monogenic hypertension Monogenic hypertension may involve mineralcorticoid-dependent or -independent increase in Na⁺ transport. Diagnosis is based on routine physical examination, blood pressure measurement and laboratory analysis of renin, aldosterone, cortisol and potassium. Genetic testing is useful for confirming diagnosis and for differential diagnosis. Monogenic hypertension has autosomal dominant or autosomal recessive inheritance. (www.actabiomedica.it)

The Link of the Prion Protein with Ca2+ Metabolism and ROS Production, and the Possible Implication in Aβ Toxicity

The cellular prion protein (PrP^C) is an ubiquitous cell surface protein mostly expressed in neurons, where it localizes to both pre- and post-synaptic membranes. PrP^C aberrant conformers are the major components of mammalian prions, the infectious agents responsible for incurable neurodegenerative disorders. PrP^C was also proposed to bind aggregated misfolded proteins/peptides, and to mediate their neurotoxic signal. In spite of long-lasting research, a general consensus on the precise pathophysiologic mechanisms of PrP^C has not yet been reached. Here we review our recent data, obtained by comparing primary neurons from PrP-expressing and PrP-knockout mice, indicating a central role of PrP^C in synaptic transmission and Ca²⁺ homeostasis. Indeed, by controlling gene expression and signaling cascades, PrP^C is able to optimize glutamate secretion and regulate Ca²⁺ entry via store-operated channels and ionotropic glutamate receptors, thereby protecting neurons from threatening Ca²⁺ overloads and excitotoxicity. We will also illustrate and discuss past and unpublished results demonstrating that Aβ oligomers perturb Ca²⁺ homeostasis and cause abnormal mitochondrial accumulation of reactive oxygen species by possibly affecting the PrP-dependent downregulation of Fyn kinase activity.

Genetic testing for Refsum disease

We reviewed the scientific literature and disease guidelines in order to summarize the clinical utility of genetic testing for Refsum disease. The disease has autosomal recessive inheritance, unknown prevalence, and is caused by variations in PEX7 and PHYH genes. Clinical diagnosis is based on clinical findings, ophthalmological examination, electroretinography, optical coherence tomography and phytanic acid assay. The genetic test is useful for confirming diagnosis, for differential diagnosis, couple risk assessment and access to clinical trials.

Genetic testing for cone rod dystrophies

We studied the scientific literature and disease guidelines in order to summarize the clinical utility of the genetic test for cone rod dystrophies (CORDs). CORDs are caused by variations in the ABCA4, ADAM9, AIPL1, C8orf37, CACNA1F, CACNA2D4, CDHR1, CNGA3, CRX, DRAM2, GUCA1A, GUCY2D, HRG4, KCNV2, PDE6C, PITPNM3, POC1B, PROM1, PRPH2, RAB28, RAX2, RIMS1, RPGRIP1, RPGR SEMA4A, TTLL5 genes, with an overall prevalence of 1 per 40 000. Most genes have autosomal recessive inheritance; the others have autosomal dominant or X-linked recessive transmission. Clinical diagnosis is based on clinical findings, color vision testing, ophthalmological examination and electroretinography. The genetic test is useful for confirming diagnosis, and for differential diagnosis, couple risk assessment and access to clinical trials.

Genetic testing for Stargardt macular dystrophy

We studied the scientific literature and disease guidelines in order to summarize the clinical utility of genetic testing for Stargardt macular dystrophy (STGD). STGD is mostly inherited in an autosomal recessive manner and rarely in an autosomal dominant manner, with an overall prevalence of 1-5 per 10 000 live births. It is caused by variations in the ABCA4, CNGB3, ELOVL4, PRPH2 and PROM1 genes. Clinical diagnosis is based on ophthalmological examination, fluorescein angiography, electroretinography, visual field testing, optical coherence tomography and color testing. The genetic test is useful for confirming diagnosis, and for differential diagnosis, couple risk assessment and access to clinical trials.

Genetic testing for Mendelian cataract

We studied the scientific literature and disease guidelines in order to summarize the clinical utility of the genetic test for Mendelian cataract (MC). MC is caused by variations in the AGK, BFSP1, BFSP2, CHMP4B, CRYAA, CRYAB, CRYBA1, CRYBA2, CRYBA4, CRYBB1, CRYBB2, CRYBB3, CRYGC, CRYGD, CRYGS, EPHA2, EYA1, FYCO1, FOXE3, FTL, GALK1, GCNT2, GJA3, GJA8, HSF4, LEMD2, LIM2, LSS, MAF, MIP, NHS, PITX3, PAX6, SIPA1L3, SLC16A12, TDRD7, UNC45B, VIM, VSX, and WFS1 genes. The overall prevalence of congenital forms is 71 per 100 000, whereas there is insufficient data to determine the prevalence of the juvenile and age-related forms. Clinical diagnosis is based on clinical findings, age of onset, family history, ophthalmological examination and slit-lamp examination. The genetic test is useful for confirming diagnosis, and for differential diagnosis, couple risk assessment and access to clinical trials.

Genetic testing for Senior-Loken syndrome

We studied the scientific literature and disease guidelines in order to summarize the clinical utility of genetic testing for Senior- Loken syndrome (SLSN). SLSN is inherited in an autosomal recessive manner, has a prevalence of one in a million, and is caused by variations in CEP164, CEP290, INVS, IQCB1, NPHP1, NPHP3, NPHP4, SDCCAG8, TRAF3IP1 and WDR19 genes. Clinical diagnosis is based on kidney (urine analysis, abdominal ultrasound, kidney function) and eye assessment (visual acuity test, fundus examination, refraction defects, color testing and electroretinography). The genetic test is useful for confirming diagnosis, and for differential diagnosis, couple risk assessment and access to clinical trials.

Genetic testing for achromatopsia

We studied the scientific literature and disease guidelines in order to summarize the clinical utility of genetic testing for achromatopsia. The disease has autosomal recessive inheritance, a prevalence of 1/30000-1/50000, and is caused by mutations in the CNGB3, CNGA3, GNAT2, PDE6C, ATF6 and PDE6H genes. Clinical diagnosis is by ophthalmological examination, color vision testing and electrophysiological testing. Genetic testing is useful for confirming diagnosis and for differential diagnosis, couple risk assessment and access to clinical trials.

Genetic testing for choroideremia

We studied the scientific literature and disease guidelines in order to summarize the clinical utility of the genetic test for choroideremia (CHM). CHM is an inherited X-linked recessive disorder associated with variations in the CHM gene. The overall prevalence of CHM varies from 1 in 50 000 to 1 in 100 000. Clinical diagnosis is based on clinical findings, ophthalmological examination, visual field, fundus autofluorescence, optical coherence tomography and electroretinography. The genetic test is useful for confirming diagnosis and for differential diagnosis, couple risk assessment and access to clinical trials.

Forty years later: Mitochondria as therapeutic targets in muscle diseases

The hypothesis that mitochondrial dysfunction can be a general mechanism for cell death in muscle diseases is 40 years old. The key elements of the proposed pathogenetic sequence (cytosolic Ca2+ overload followed by excess mitochondrial Ca2+ uptake, functional and then structural damage of mitochondria, energy shortage, worsened elevation of cytosolic Ca2+ levels, hypercontracture of muscle fibers, cell necrosis) have been confirmed in amazing detail by subsequent work in a variety of models. The explicit implication of the hypothesis was that it "may provide the basis for a more rational treatment for some conditions even before their primary causes are known" (Wrogemann and Pena, 1976, Lancet, 1, 672-674). This prediction is being fulfilled, and the potential of mitochondria as pharmacological targets in muscle diseases may soon become a reality, particularly through inhibition of the mitochondrial permeability transition pore and its regulator cyclophilin D.

Melanocytes from Patients Affected by Ullrich Congenital Muscular Dystrophy and Bethlem Myopathy have Dysfunctional Mitochondria That Can be Rescued with Cyclophilin Inhibitors

Ullrich congenital muscular dystrophy and Bethlem myopathy are caused by mutations in collagen VI (ColVI) genes, which encode an extracellular matrix protein; yet, mitochondria play a major role in disease pathogenesis through a short circuit caused by inappropriate opening of the permeability transition pore, a high-conductance channel, which causes a shortage in ATP production. We find that melanocytes do not produce ColVI yet they bind it at the cell surface, suggesting that this protein may play a trophic role and that its absence may cause lesions similar to those seen in skeletal muscle. We show that mitochondria in melanocytes of Ullrich congenital muscular dystrophy and Bethlem myopathy patients display increased size, reduced matrix density, and disrupted cristae, findings that suggest a functional impairment. In keeping with this hypothesis, mitochondria (i) underwent anomalous depolarization after inhibition of the F-ATP synthase with oligomycin, and (ii) displayed decreased respiratory reserve capacity. The non-immunosuppressive cyclophilin inhibitor NIM811 prevented mitochondrial depolarization in response to oligomycin in melanocytes from both Ullrich congenital muscular dystrophy and Bethlem myopathy patients, and partially restored the respiratory reserve of melanocytes from one Bethlem myopathy patient. These results match our recent findings on melanocytes from patients affected by Duchenne muscular dystrophy (Pellegrini et al., 2013), and suggest that skin biopsies may represent a minimally invasive tool to investigate mitochondrial dysfunction and to evaluate drug efficacy in ColVI-related myopathies and possibly in other muscle wasting conditions like aging sarcopenia.

Monoamine oxidase inhibition prevents mitochondrial dysfunction and apoptosis in myoblasts from patients with collagen VI myopathies

Although mitochondrial dysfunction and oxidative stress have been proposed to play a crucial role in several types of muscular dystrophy (MD), whether a causal link between these two alterations exists remains an open question. We have documented that mitochondrial dysfunction through opening of the permeability transition pore plays a key role in myoblasts from patients as well as in mouse models of MD, and that oxidative stress caused by monoamine oxidases (MAO) is involved in myofiber damage. In the present study we have tested whether MAO-dependent oxidative stress is a causal determinant of mitochondrial dysfunction and apoptosis in myoblasts from patients affected by collagen VI myopathies. We find that upon incubation with hydrogen peroxide or the MAO substrate tyramine myoblasts from patients upregulate MAO-B expression and display a significant rise in reactive oxygen species (ROS) levels, with concomitant mitochondrial depolarization. MAO inhibition by pargyline significantly reduced both ROS accumulation and mitochondrial dysfunction, and normalized the increased incidence of apoptosis in myoblasts from patients. Thus, MAO-dependent oxidative stress is causally related to mitochondrial dysfunction and cell death in myoblasts from patients affected by collagen VI myopathies, and inhibition of MAO should be explored as a potential treatment for these diseases.

Molecular and morphologic characterization of superficial- and deep-subcutaneous adipose tissue subdivisions in human obesity

OBJECTIVE

Human abdominal subcutaneous white adipose tissue (SAT) is composed of two different subcompartments: a "superficial" SAT (SSAT), located between the skin and a fibrous-fascia plane; and a deeper SAT, located under this fibrous fascia plane, indicated as "deep" SAT (DSAT).

DESIGN AND METHODS

In order to investigate whether SSAT and DSAT have different molecular and morphological features, paired SSAT/DSAT biopsies were collected from 10 female obese patients and used for microarray and morphologic analysis. The stroma-vascular fraction cells were also isolated from both depots and cultured in vitro to assess the lipid accumulation rate.

RESULTS

SSAT and DSAT displayed different patterns of gene expression, mainly for metabolic and inflammatory genes, respectively. Detailed gene expression analysis indicated that several metabolic genes, including adiponectin, are preferentially expressed in SSAT, whereas inflammatory genes are over-expressed in DSAT. Despite a similar lipid accumulation rate in vitro, in vivo SSAT showed a significant adipocyte hypertrophy together with a significantly lower inflammatory infiltration and vascular vessel lumen mean size, when compared to DSAT.

CONCLUSIONS

These data show that, SSAT and DSAT are functionally and morphologically different and emphasize the importance of considering independent these two adipose depots when investigating SAT biology and obesity complications.

Differences in visceral fat and fat bacterial colonization between ulcerative colitis and Crohn's disease. An in vivo and in vitro study

Crohn's disease (CD) is notably characterized by the expansion of visceral fat with small adipocytes expressing a high proportion of anti-inflammatory genes. Conversely, visceral fat depots in ulcerative colitis (UC) patients have never been characterized. Our study aims were a) to compare adipocyte morphology and gene expression profile and bacterial translocation in omental (OM) and mesenteric (MES) adipose tissue of patients with UC and CD, and b) to investigate the effect of bacterial infection on adipocyte proliferation in vitro. Specimens of OM and MES were collected from 11 UC and 11 CD patients, processed and examined by light microscopy. Gene expression profiles were evaluated in adipocytes isolated from visceral adipose tissue using microarray and RTqPCR validations. Bacteria within adipose tissue were immuno-detected by confocal scanning laser microscopy. Adipocytes were incubated with Enterococcus faecalis and cells counted after 24 h. Morphology and molecular profile of OM and MES revealed that UC adipose tissue is less inflamed than CD adipose tissue. Genes linked to inflammation, bacterial response, chemotaxis and angiogenesis were down-regulated in adipocytes from UC compared to CD, whereas genes related to metallothioneins, apoptosis pathways and growth factor binding were up-regulated. A dense perinuclear positivity for Enterococcus faecalis was detected in visceral adipocytes from CD, whereas positivity was weak in UC. In vitro bacterial infection was associated with a five-fold increase in the proliferation rate of OM preadipocytes. Compared to UC, visceral adipose tissue from CD is more inflamed and more colonized by intestinal bacteria, which increase adipocyte proliferation. The influence of bacteria stored within adipocytes on the clinical course of IBD warrants further investigations.

Melanocytes--a novel tool to study mitochondrial dysfunction in Duchenne muscular dystrophy

Dystrophin is a subsarcolemmal protein that, by linking the actin cytoskeleton to the extracellular matrix via dystroglycans, is critical for the integrity of muscle fibers. Here, we report that epidermal melanocytes, obtained from conventional skin biopsy, express dystrophin with a restricted localization to the plasma membrane facing the dermal–epidermal junction. In addition the full-length muscle isoform mDp427 was clearly detectable in melanocyte cultures as assessed by immunohistochemistry, RNA, and Western blot analysis. Melanocytes of Duchenne muscular dystrophy (DMD) patients did not express dystrophin, and the ultrastructural analysis revealed typical mitochondrial alterations similar to those occurring in myoblasts from the same patients. Mitochondria of melanocytes from DMD patients readily accumulated tetramethylrhodamine methyl ester, indicating that they are energized irrespective of the presence of dystrophin but, at variance from mitochondria of control donors, depolarized upon the addition of oligomycin, suggesting that they are affected by a latent dysfunction unmasked by inhibition of the ATP synthase. Pure melanocyte cultures can be readily obtained by conventional skin biopsies and may be a feasible and reliable tool alternative to muscle biopsy for functional studies in dystrophinopathies. The mitochondrial dysfunction occurring in DMD melanocytes could represent a promising cellular biomarker for monitoring dystrophinopathies also in response to pharmacological treatments. J. Cell. Physiol. 228: 1323–1331, 2013. © 2012 Wiley Periodicals, Inc.

Cross talk between plasma membrane Na(+)/Ca (2+) exchanger-1 and TRPC/Orai-containing channels: key players in arterial hypertension

Arterial smooth muscle (ASM) Na(+)/Ca(2+) exchanger type 1 (NCX1) and TRPC/Orai-containing receptor/store-operated cation channels (ROC/SOC) are clustered with α2 Na(+) pumps in plasma membrane microdomains adjacent to the underlying junctional sarcoplasmic reticulum. This arrangement enables these transport proteins to function as integrated units to help regulate local Na(+) metabolism, Ca(2+) signaling, and arterial tone. They thus influence vascular resistance and blood pressure (BP). For instance, upregulation of NCX1 and TRPC6 has been implicated in the pathogenesis of high BP in several models of essential hypertension. The models include ouabain-induced hypertensive rats, Milan hypertensive rats, and Dahl salt-sensitive hypertensive rats, all of which exhibit elevated plasma ouabain levels. We suggest that these molecular mechanisms are key contributors to the increased vascular resistance ("whole body autoregulation") that elevates BP in essential hypertension. Enhanced expression and function of ASM NCX1 and TRPC/Orai1-containing channels in hypertension implies that these proteins are potential targets for pharmacological intervention.

Activation of c-SRC underlies the differential effects of ouabain and digoxin on Ca(2+) signaling in arterial smooth muscle cells

Cardiotonic steroids (CTS) of the strophanthus and digitalis families have opposing effects on long-term blood pressure (BP). This implies hitherto unrecognized divergent signaling pathways for these CTS. Prolonged ouabain treatment upregulates Ca(2+) entry via Na(+)/Ca(2+) exchanger-1 (NCX1) and TRPC6 gene-encoded receptor-operated channels in mesenteric artery smooth muscle cells (ASMCs) in vivo and in vitro. Here, we test the effects of digoxin on Ca(2+) entry and signaling in ASMC. In contrast to ouabain treatment, the in vivo administration of digoxin (30 μg·kg(-1)·day(-1) for 3 wk) did not raise BP and had no effect on resting cytolic free Ca(2+) concentration ([Ca(2+)](cyt)) or phenylephrine-induced Ca(2+) signals in isolated ASMCs. Expression of transporters in the α2 Na(+) pump-NCX1-TRPC6 Ca(2+) signaling pathway was not altered in arteries from digoxin-treated rats. Upregulated α2 Na(+) pumps and a phosphorylated form of the c-SRC protein kinase (pY419-Src, ~4.5-fold) were observed in ASMCs from rats treated with ouabain but not digoxin. Moreover, in primary cultured ASMCs from normal rats, treatment with digoxin (100 nM, 72 h) did not upregulate NCX1 and TRPC6 but blocked the ouabain-induced upregulation of these transporters. Pretreatment of ASMCs with the c-Src inhibitor PP2 (1 μM; 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine) but not its inactive analog eliminated the effect of ouabain on NCX1 and TRPC6 expression and ATP-induced Ca(2+) entry. Thus, in contrast to ouabain, the interaction of digoxin with α2 Na(+) pumps is unable to activate c-Src phosphorylation and upregulate the downstream NCX1-TRPC6 Ca(2+) signaling pathway in ASMCs. The inability of digoxin to upregulate c-Src may underlie its inability to raise long-term BP.

A novel missense mutation in the signal peptide of the human POMC gene: a possible additional link between early-onset type 2 diabetes and obesity

Rare mutations in several genes have a critical role in the control of homeostatic mechanisms such as food-intake, energy balance and glucose metabolism. In this study, we performed a mutational screening in a 58-year-old woman presenting early-onset type 2 diabetes and central obesity. The entire coding regions of MC4R, MC3R, HNF1A, GCK and POMC (pro-opiomelanocortin) genes were analyzed by direct sequencing. A new missense mutation was identified within the POMC gene signal peptide sequence, resulting in a heterozygous substitution of an arginine for a glycine at codon 15 (p.A15G) that was excluded in 300 healthy normal weight controls. The mutation segregated in the family and was associated with overweight, type 2 diabetes, hypertension and coronary heart disease in the carriers. Functional studies demonstrated that POMC protein was not detectable in β-TC3 cells transfected with A15G-POMC vector as well as in their culture media, despite POMC mRNA levels were comparable for amount and stability to those of wild-type-transfected cells. In silico RNA folding prediction indicated that the mutation gives rise to a different RNA secondary structure, suggesting that it might affect translation and protein synthesis. To the best of our knowledge, this is the first report addressing the functional consequences of a mutation in the signal peptide of POMC. These findings further support the hypothesis that POMC-derived peptides might have a role in the control of peripheral glucose metabolism and suggest that disruption of central POMC secretion might represent an additional link between type 2 diabetes and obesity.

Visceral adipocytes: old actors in obesity and new protagonists in Crohn's disease?

OBJECTIVE

Crohn's disease (CD) is a chronic inflammatory bowel disease characterised by a peculiar accumulation of mesenteric adipose tissue covering the inflamed intestinal wall.

METHODS

The authors characterised different adipose tissue compartments of patients with CD using morphological and molecular techniques and compared them to those of subjects with obesity (OB) and healthy subjects with normal weight (N). Adipose tissue samples were taken from subcutaneous adipose tissue, omental visceral adipose tissue (VAT) and healthy mesenteric depot (hMES), as well as from fat wrapping the affected (unhealthy) intestinal tracts (uhMES). Microarray analyses, validated by real-time quantitative PCR technique, were performed in whole adipose tissue and in isolated adipocytes.

RESULTS

The morphology of subcutaneous adipose tissue was similar in subjects with CD and those with N. In patients with CD, VAT adipocytes were smaller than those derived from uhMES and hMES and were smaller than VAT adipocytes of subjects with N. The molecular profiles of CD, VAT and uhMES were characterised by upregulation of genes related to inflammation and downregulation of those involved in lipid metabolism. Adipocytes isolated from VAT of subjects with CD and those with OB exhibited similar upregulation of genes involved in inflammation and immunity. VAT adipocytes of patients with CD compared to those of patients with OB also showed a greater upregulation of several anti-inflammatory genes.

CONCLUSION

In patients with CD, VAT distant from uhMES is affected by inflammation and displays features similar to those of VAT of patients with severe OB. The small diameter of VAT adipocytes of CD, together with their high expression of anti-inflammatory genes, suggests a potentially protective role for this tissue. VAT adipocytes may play an important role in the pathophysiology and/or activity of CD.

Increased arterial smooth muscle Ca2+ signaling, vasoconstriction, and myogenic reactivity in Milan hypertensive rats

The Milan hypertensive strain (MHS) rats are a genetic model of hypertension with adducin gene polymorphisms linked to enhanced renal tubular Na(+) reabsorption. Recently we demonstrated that Ca(2+) signaling is augmented in freshly isolated mesenteric artery myocytes from MHS rats. This is associated with greatly enhanced expression of Na(+)/Ca(2+) exchanger-1 (NCX1), C-type transient receptor potential (TRPC6) protein, and sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2) compared with arteries from Milan normotensive strain (MNS) rats. Here, we test the hypothesis that the enhanced Ca(2+) signaling in MHS arterial smooth muscle is directly reflected in augmented vasoconstriction [myogenic and phenylephrine (PE)-evoked responses] in isolated mesenteric small arteries. Systolic blood pressure was higher in MHS (145 ± 1 mmHg) than in MNS (112 ± 1 mmHg; P < 0.001; n = 16 each) rats. Pressurized mesenteric resistance arteries from MHS rats had significantly augmented myogenic tone and reactivity and enhanced constriction to low-dose (1-100 nM) PE. Isolated MHS arterial myocytes exhibited approximately twofold increased peak Ca(2+) signals in response to 5 μM PE or ATP in the absence and presence of extracellular Ca(2+). These augmented responses are consistent with increased vasoconstrictor-evoked sarcoplasmic reticulum (SR) Ca(2+) release and increased Ca(2+) entry, respectively. The increased SR Ca(2+) release correlates with a doubling of inositol 1,4,5-trisphosphate receptor type 1 and tripling of SERCA2 expression. Pressurized MHS arteries also exhibited a ∼70% increase in 100 nM ouabain-induced vasoconstriction compared with MNS arteries. These functional alterations reveal that, in a genetic model of hypertension linked to renal dysfunction, multiple mechanisms within the arterial myocytes contribute to enhanced Ca(2+) signaling and myogenic and vasoconstrictor-induced arterial constriction. MHS rats have elevated plasma levels of endogenous ouabain, which may initiate the protein upregulation and enhanced Ca(2+) signaling. These molecular and functional changes provide a mechanism for the increased peripheral vascular resistance (whole body autoregulation) that underlies the sustained hypertension.

The translocator protein (peripheral benzodiazepine receptor) mediates rat-selective activation of the mitochondrial permeability transition by norbormide

We have investigated the mechanism of rat-selective induction of the mitochondrial permeability transition (PT) by norbormide (NRB). We show that the inducing effect of NRB on the PT (i) is inhibited by the selective ligands of the 18kDa outer membrane (OMM) translocator protein (TSPO, formerly peripheral benzodiazepine receptor) protoporphyrin IX, N,N-dihexyl-2-(4-fluorophenyl)indole-3-acetamide and 7-chloro-5-(4-chlorophenyl)-1,3-dihydro-1-methyl-2H-1,4-benzodiazepin-2-one; and (ii) is lost in digitonin mitoplasts, which lack an intact OMM. In mitoplasts the PT can still be induced by the NRB cationic derivative OL14, which contrary to NRB is also effective in intact mitochondria from mouse and guinea pig. We conclude that selective NRB transport into rat mitochondria occurs via TSPO in the OMM, which allows its translocation to PT-regulating sites in the inner membrane. Thus, species-specificity of NRB toward the rat PT depends on subtle differences in the structure of TSPO or of TSPO-associated proteins affecting its substrate specificity.

In vitro and in vivo effects of metformin on human adipose tissue adiponectin

OBJECTIVE

The effects of metformin on adiponectin production are controversial and have never been investigated in human adipose tissue. We analysed whether metformin modulates, in vitro and in vivo, gene expression, protein content, and secretion of adiponectin.

METHODS

For the in vitro study, subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) samples from 5 non-diabetic obese patients were collected. For the in vivo investigation, 22 obese patients were randomly assigned to metformin+lifestyle (ML) or placebo+lifestyle (PL) intervention. SAT specimens and blood samples were collected before and after the intervention in both groups.

RESULTS

In in vitro experiments, treatment with metformin increased the expression and secretion of adiponectin in SAT, but not in VAT explants. In the in vivo study, a significant increase in adiponectin and a decreased expression of a macrophage activation marker (CD68) were observed only in SAT of the ML group.

CONCLUSION

These results demonstrate that metformin is able to up-regulate adiponectin gene expression, both in vivo and in vitro, and to stimulate adiponectin protein secretion from human SAT in vitro. It could be hypothesised that metformin-induced adiponectin increase within adipose tissue may have an unexpected role in the reduction of local inflammation.

Regulation of the inner membrane mitochondrial permeability transition by the outer membrane translocator protein (peripheral benzodiazepine receptor)

We studied the properties of the permeability transition pore (PTP) in rat liver mitochondria and in mitoplasts retaining inner membrane ultrastructure and energy-linked functions. Like mitochondria, mitoplasts readily underwent a permeability transition following Ca(2+) uptake in a process that maintained sensitivity to cyclosporin A. On the other hand, major differences between mitochondria and mitoplasts emerged in PTP regulation by ligands of the outer membrane translocator protein of 18 kDa, TSPO, formerly known as the peripheral benzodiazepine receptor. Indeed, (i) in mitoplasts, the PTP could not be activated by photo-oxidation after treatment with dicarboxylic porphyrins endowed with protoporphyrin IX configuration, which bind TSPO in intact mitochondria; and (ii) mitoplasts became resistant to the PTP-inducing effects of N,N-dihexyl-2-(4-fluorophenyl)indole-3-acetamide and of other selective ligands of TSPO. Thus, the permeability transition is an inner membrane event that is regulated by the outer membrane through specific interactions with TSPO.

Upregulation of Na+/Ca2+ exchanger and TRPC6 contributes to abnormal Ca2+ homeostasis in arterial smooth muscle cells from Milan hypertensive rats

The Milan hypertensive strain (MHS) of rats is a model for hypertension in humans. Inherited defects in renal function have been well studied in MHS rats, but the mechanisms that underlie the elevated vascular resistance are unclear. Altered Ca(2+) signaling plays a key role in the vascular dysfunction associated with arterial hypertension. Here we compared Ca(2+) signaling in mesenteric artery smooth muscle cells from MHS rats and its normotensive counterpart (MNS). Systolic blood pressure was higher in MHS than in MNS rats (144 +/- 2 vs. 113 +/- 1 mmHg, P < 0.05). Resting cytosolic free Ca(2+) concentration (measured with fura-2) and ATP-induced Ca(2+) transients were augmented in freshly dissociated arterial myocytes from MHS rats. Ba(2+) entry activated by the diacylglycerol analog 1-oleoyl-2-acetyl-sn-glycerol (a measure of receptor-operated channel activity) was much greater in MHS than MNS arterial myocytes. This correlated with a threefold upregulation of transient receptor potential canonical 6 (TRPC6) protein. TRPC3, the other component of receptor-operated channels, was marginally, but not significantly, upregulated. The expression of TRPC1/5, components of store-operated channels, was not altered in MHS mesenteric artery smooth muscle. Immunoblots also revealed that the Na(+)/Ca(2+) exchanger-1 (NCX1) was greatly upregulated in MHS mesenteric artery (by approximately 13-fold), whereas the expression of plasma membrane Ca(2+)-ATPase was not altered. Ca(2+) entry via the reverse mode of NCX1 evoked by the removal of extracellular Na(+) induced a rapid increase in cytosolic free Ca(2+) concentration that was significantly larger in MHS arterial myocytes. The expression of alpha(1)/alpha(2) Na(+) pumps in MHS mesenteric arteries was not changed. Immunocytochemical observations showed that NCX1 and TRPC6 are clustered in plasma membrane microdomains adjacent to the underlying sarcoplasmic reticulum. In summary, MHS arteries exhibit upregulated TRPC6 and NCX1 and augmented Ca(2+) signaling. We suggest that the increased Ca(2+) signaling contributes to the enhanced vasoconstriction and elevated blood pressure in MHS rats.

Upregulation of Na+ and Ca2+ transporters in arterial smooth muscle from ouabain-induced hypertensive rats

Prolonged ouabain administration (25 microg kg(-1) day(-1) for 5 wk) induces "ouabain hypertension" (OH) in rats, but the molecular mechanisms by which ouabain elevates blood pressure are unknown. Here, we compared Ca(2+) signaling in mesenteric artery smooth muscle cells (ASMCs) from normotensive (NT) and OH rats. Resting cytosolic free Ca(2+) concentration ([Ca(2+)](cyt); measured with fura-2) and phenylephrine-induced Ca(2+) transients were augmented in freshly dissociated OH ASMCs. Immunoblots revealed that the expression of the ouabain-sensitive alpha(2)-subunit of Na(+) pumps, but not the predominant, ouabain-resistant alpha(1)-subunit, was increased (2.5-fold vs. NT ASMCs) as was Na(+)/Ca(2+) exchanger-1 (NCX1; 6-fold vs. NT) in OH arteries. Ca(2+) entry, activated by sarcoplasmic reticulum (SR) Ca(2+) store depletion with cyclopiazonic acid (SR Ca(2+)-ATPase inhibitor) or caffeine, was augmented in OH ASMCs. This reflected an augmented expression of 2.5-fold in OH ASMCs of C-type transient receptor potential TRPC1, an essential component of store-operated channels (SOCs); two other components of some SOCs were not expressed (TRPC4) or were not upregulated (TRPC5). Ba(2+) entry activated by the diacylglycerol analog 1-oleoyl-2-acetyl-sn-glycerol [a measure of receptor-operated channel (ROC) activity] was much greater in OH than NT ASMCs. This correlated with a sixfold upregulation of TRPC6 protein, a ROC family member. Importantly, in primary cultured mesenteric ASMCs from normal rats, 72-h treatment with 100 nM ouabain significantly augmented NCX1 and TRPC6 protein expression and increased resting [Ca(2+)](cyt) and ROC activity. SOC activity was also increased. Silencer RNA knockdown of NCX1 markedly downregulated TRPC6 and eliminated the ouabain-induced augmentation; silencer RNA knockdown of TRPC6 did not affect NCX1 expression but greatly attenuated its upregulation by ouabain. Clearly, NCX1 and TRPC6 expression are interrelated. Thus, prolonged ouabain treatment upregulates the Na(+) pump alpha(2)-subunit-NCX1-TRPC6 (ROC) Ca(2+) signaling pathway in arterial myocytes in vitro as well as in vivo. This may explain the augmented myogenic responses and enhanced phenylephrine-induced vasoconstriction in OH arteries (83) as well as the high blood pressure in OH rats.

Orai1, a critical component of store-operated Ca2+ entry, is functionally associated with Na+/Ca2+ exchanger and plasma membrane Ca2+ pump in proliferating human arterial myocytes

Ca(2+) entry through store-operated channels (SOCs) in the plasma membrane plays an important role in regulation of vascular smooth muscle contraction, tone, and cell proliferation. The C-type transient receptor potential (TRPC) channels have been proposed as major candidates for SOCs in vascular smooth muscle. Recently, two families of transmembrane proteins, Orai [also known as Ca(2+) release-activated Ca(2+) channel modulator (CRACM)] and stromal interacting molecule 1 (STIM1), were shown to be essential for the activation of SOCs mainly in nonexcitable cells. Here, using small interfering RNA, we show that Orai1 plays an essential role in activating store-operated Ca(2+) entry (SOCE) in primary cultured proliferating human aortic smooth muscle cells (hASMCs), whereas Orai2 and Orai3 do not contribute to SOCE. Knockdown of Orai1 protein expression significantly attenuated SOCE. Moreover, inhibition of Orai1 downregulated expression of Na(+)/Ca(2+) exchanger type 1 (NCX1) and plasma membrane Ca(2+) pump isoform 1 (PMCA1). The rate of cytosolic free Ca(2+) concentration decay after Ca(2+) transients in Ca(2+)-free medium was also greatly decreased under these conditions. This reduction of Ca(2+) extrusion, presumably via NCX1 and PMCA1, may be a compensation for the reduced SOCE. Immunocytochemical observations indicate that Orai1 and NCX1 are clustered in plasma membrane microdomains. Cell proliferation was attenuated in hASMCs with disrupted Orai1 expression and reduced SOCE. Thus Orai1 appears to be a critical component of SOCE in proliferating vascular smooth muscle cells, and may therefore be a key player during vascular growth and remodeling.

Low-dose ouabain constricts small arteries from ouabain-hypertensive rats: implications for sustained elevation of vascular resistance

Prolonged ouabain administration to normal rats causes sustained blood pressure (BP) elevation. This ouabain-induced hypertension (OH) has been attributed, in part, to the narrowing of third-order resistance arteries (approximately 320 microm internal diameter) as a result of collagen deposition in the artery media. Here we describe the structural and functional properties of fourth-order mesenteric small arteries from control and OH rats, including the effect of low-dose ouabain on myogenic tone in these arteries. Systolic BP in OH rats was 138 +/- 3 versus 124 +/- 4 mmHg in controls (P < 0.01). Pressurized (70 mmHg) control and OH arteries, with only a single layer of myocytes, both had approximately 165-microm internal diameters and approximately 20-microm wall thicknesses. Even after fixation, despite vasoconstriction, the diameters and wall thicknesses did not differ between control and OH fourth-order arteries, whereas in third-order arteries, both parameters were significantly smaller in OH than in controls. Myogenic reactivity was significantly augmented in OH fourth-order arteries. Nevertheless, phenylephrine- (1 microM) and high K(+)-induced vasoconstrictions and acetylcholine-induced vasodilation were comparable in control and OH arteries. Vasoconstrictions induced by 5 microM phenylephrine and by 10 mM caffeine in Ca(2+)-free media indicated that releasable sarcoplasmic reticulum Ca(2+) stores were normal in OH arteries. Importantly, 100 nM ouabain constricted both control and OH arteries by approximately 26 microm, indicating that this response was not downregulated in OH rats. This maximal ouabain-induced constriction corresponds to a approximately 90% increase in resistance to flow in these small arteries; thus ouabain at EC(50) of approximately 0.66 nM should raise resistance by approximately 35%. We conclude that dynamic constriction in response to circulating nanomolar ouabain in small arteries likely makes a major contribution to the increased vascular tone and BP in OH rats.

Assessing the molecular basis for rat-selective induction of the mitochondrial permeability transition by norbormide

It was recently demonstrated that the rat-selective toxicant norbormide also induces rat-selective opening of the permeability transition pore (PTP) in isolated mitochondria. Norbormide is a mixture of endo and exo stereoisomers; however, only the endo forms are lethal to rats. In the present study we tested both endo and exo isomers as well as neutral and cationic derivatives of norbormide to: (i) verify if the PTP-regulatory activity by norbormide is stereospecific; (ii) define the structural features of norbormide responsible for PTP-activation, (iii) elucidate the basis for the drug species-specificity. Our results show that: (i) norbormide isomers affect PTP in a rat-selective fashion; however, no relevant differences between lethal and non-lethal forms are observed suggesting that drug regulation of PTP-activity and lethality in rats are unrelated phenomena; (ii) a (phenylvinyl)pyridine moiety represents the key element conferring the PTP-activating effect; (iii) cationic derivatives of rat-active compounds accumulate in the matrix via the membrane potential and activate the PTP also in mouse and guinea pig mitochondria. These findings suggest that the norbormide-sensitive PTP-target is present in all species examined, and is presumably located on the matrix side. The species-selectivity may depend on the unique properties of a transport system allowing drug internalisation in rat mitochondria.

Synthesis and activity studies of analogues of the rat selective toxicant norbormide

Norbormide [5-(alpha-hydroxy-alpha-2-pyridylbenzyl)-7-(alpha-2-pyridylbenzylidene)-5-norbornene-2,3-dicarboximide] (NRB, 1), an existing but infrequently used rodenticide, is known to be uniquely toxic to rats but relatively harmless to other rodents and mammals. A series of NRB-related analogues were prepared to investigate the structural features responsible for, and the in vitro biological markers indicative of, in vivo lethality of the parent molecule in rats. Their synthesis and biological evaluation (vasoconstriction, vasodilation, mitochondrial dysfunction, cardiotoxicity and lethality) is described.

Increased longevity and refractoriness to Ca(2+)-dependent neurodegeneration in Surf1 knockout mice

Leigh syndrome associated with cytochrome c oxidase (COX) deficiency is a mitochondrial disorder usually caused by mutations of SURF1, a gene encoding a putative COX assembly factor. We present here a Surf1-/- recombinant mouse obtained by inserting a loxP sequence in the open reading frame of the gene. The frequency of -/-, +/+ and +/- genotypes in newborn mice followed a mendelian distribution, indicating that the ablation of Surf1 is compatible with postnatal survival. The biochemical and assembly COX defect was present in Surf1(loxP)-/- mice, but milder than in humans. Surprisingly, not only these animals failed to show spontaneous neurodegeneration at any age, but they also displayed markedly prolonged lifespan, and complete protection from Ca(2+)-dependent neurotoxicity induced by kainic acid. Experiments on primary neuronal cultures showed markedly reduced rise of cytosolic and mitochondrial Ca(2+) in Surf1(loxP)-/- neurons, and reduced mortality, compared to controls. The mitochondrial membrane potential was unchanged in KO versus wild-type neurons, suggesting that the effects of the ablation of Surf1 on Ca(2+) homeostasis, and possibly on longevity, may be independent, at least in part, from those on COX assembly and mitochondrial bioenergetics.