The heterozygous R155C VCP mutation: Toxic in humans! Harmless in mice?

Heterozygous missense mutations in the human VCP gene cause inclusion body myopathy associated with Paget disease of bone and fronto-temporal dementia (IBMPFD) and amyotrophic lateral sclerosis (ALS). The exact molecular mechanisms by which VCP mutations cause disease manifestation in different tissues are incompletely understood. In the present study, we report the comprehensive analysis of a newly generated R155C VCP knock-in mouse model, which expresses the ortholog of the second most frequently occurring human pathogenic VCP mutation. Heterozygous R155C VCP knock-in mice showed decreased plasma lactate, serum albumin and total protein concentrations, platelet numbers, and liver to body weight ratios, and increased oxygen consumption and CD8+/Ly6C + T-cell fractions, but none of the typical human IBMPFD or ALS pathologies. Breeding of heterozygous mice did not yield in the generation of homozygous R155C VCP knock-in animals. Immunoblotting showed identical total VCP protein levels in human IBMPFD and murine R155C VCP knock-in tissues as compared to wild-type controls. However, while in human IBMPFD skeletal muscle tissue 70% of the total VCP mRNA was derived from the mutant allele, in R155C VCP knock-in mice only 5% and 7% mutant mRNA were detected in skeletal muscle and brain tissue, respectively. The lack of any obvious IBMPFD or ALS pathology could thus be a consequence of the very low expression of mutant VCP. We conclude that the increased and decreased fractions of the R155C mutant VCP mRNA in man and mice, respectively, are due to missense mutation-induced, divergent alterations in the biological half-life of the human and murine mutant mRNAs. Furthermore, our work suggests that therapy approaches lowering the expression of the mutant VCP mRNA below a critical threshold may ameliorate the intrinsic disease pathology.

Correction: Heteromeric p97/p97R155C Complexes Induce Dominant Negative Changes in Wild-Type and Autophagy 9-Deficient Dictyostelium strains.

[This corrects the article DOI: 10.1371/journal.pone.0046879.].

Serum markers for early detection of patients with mesenteric ischemia after cardiac surgery.

OBJECTIVE: Mesenteric ischemia (MESI) is a rare but often fatal complication in patients after cardiac surgery. Non-specific clinical symptoms and lack of specific laboratory parameters complicate the diagnosis. We evaluated potential serum markers for MESI in cardiac surgery patients. METHODS: Between March and October 2012, serial serum samples of 567 elective cardiac surgery patients were collected 1, 24, and 48 h after the operation, and concentrations of potential markers for MESI [α-glutathione-S-transferase (αGST), intestinal fatty-acid-binding protein (iFABP), and D-lactate] were measured retrospectively. In patients requiring laparotomy, blood samples obtained 72, 48, 24, and 12 h before the laparotomy were additionally measured and compared to all other patients (control group). RESULTS: Laparotomy was performed in 18 patients at 11±7 days after cardiac surgery. MESI was found in 9/18 patients. Already 1 h after cardiac surgery, the serum concentrations of D-lactate (37±18 vs. 25±20 nmol/mL, p<0.01) and αGST (82±126 vs. 727±1382 µg/L, p<0.01) in patients undergoing laparotomy were increased compared to the control group. Between patients with and without MESI, differences were only found for iFABP 24 h after cardiac surgery (1.1±0.4 vs. 2.9±0.6 ng/mL, p=0.04) and up to 72 h before laparotomy (0.56±0.72 vs. 2.51±1.96 ng/mL, p=0.01). CONCLUSIONS: D-lactate and αGST were early markers for gastrointestinal complications after cardiac surgery. Before laparotomy, lowered iFABP levels indicated MESI. Routinely used, these markers can help identify patients with gastrointestinal complications after cardiac surgery early, and might be useful for the evaluation of new therapeutic or preventive strategies.

Noncanonical thyroid hormone signaling mediates cardiometabolic effects in vivo.

Thyroid hormone (TH) and TH receptors (TRs) α and ß act by binding to TH response elements (TREs) in regulatory regions of target genes. This nuclear signaling is established as the canonical or type 1 pathway for TH action. Nevertheless, TRs also rapidly activate intracellular second-messenger signaling pathways independently of gene expression (noncanonical or type 3 TR signaling). To test the physiological relevance of noncanonical TR signaling, we generated knockin mice with a mutation in the TR DNA-binding domain that abrogates binding to DNA and leads to complete loss of canonical TH action. We show that several important physiological TH effects are preserved despite the disruption of DNA binding of TRα and TRß, most notably heart rate, body temperature, blood glucose, and triglyceride concentration, all of which were regulated by noncanonical TR signaling. Additionally, we confirm that TRE-binding-defective TRß leads to disruption of the hypothalamic-pituitary-thyroid axis with resistance to TH, while mutation of TRα causes a severe delay in skeletal development, thus demonstrating tissue- and TR isoform-specific canonical signaling. These findings provide in vivo evidence that noncanonical TR signaling exerts physiologically important cardiometabolic effects that are distinct from canonical actions. These data challenge the current paradigm that in vivo physiological TH action is mediated exclusively via regulation of gene transcription at the nuclear level.

Human Ex-Vivo Liver Model for Acetaminophen-induced Liver Damage.

Reliable test systems to identify hepatotoxicity are essential to predict unexpected drug-related liver injury. Here we present a human ex-vivo liver model to investigate acetaminophen-induced liver injury. Human liver tissue was perfused over a 30 hour period with hourly sampling from the perfusate for measurement of general metabolism and clinical parameters. Liver function was assessed by clearance of indocyanine green (ICG) at 4, 20 and 28 hours. Six pieces of untreated human liver specimen maintained stable liver function over the entire perfusion period. Three liver sections incubated with low-dose acetaminophen revealed strong damage, with ICG half-lives significantly higher than in non-treated livers. In addition, the release of microRNA-122 was significantly higher in acetaminophen-treated than in non-treated livers. Thus, this model allows for investigation of hepatotoxicity in human liver tissue upon applying drug concentrations relevant in patients.

Sex-specific phenotypes of hyperthyroidism and hypothyroidism in mice.

BACKGROUND: Thyroid dysfunction is more common in the female population, however, the impact of sex on disease characteristics has rarely been addressed. Using a murine model, we asked whether sex has an influence on phenotypes, thyroid hormone status, and thyroid hormone tissue response in hyper- and hypothyroidism. METHODS: Hypo- and hyperthyroidism were induced in 5-month-old female and male wildtype C57BL/6N mice, by LoI/MMI/ClO4 (-) or T4 i.p. treatment over 7 weeks, and control animals underwent sham treatment (N = 8 animals/sex/treatment). Animals were investigated for impact of sex on body weight, food and water intake, body temperature, heart rate, behaviour (locomotor activity, motor coordination, and strength), liver function, serum thyroid hormone status, and cellular TH effects on gene expression in brown adipose tissue, heart, and liver. RESULTS: Male and female mice showed significant differences in behavioural, functional, metabolic, biochemical, and molecular traits of hyper- and hypothyroidism. Hyperthyroidism resulted in increased locomotor activity in female mice but decreased muscle strength and motor coordination preferably in male animals. Hypothyroidism led to increased water intake in male but not female mice and significantly higher serum cholesterol in male mice. Natural sex differences in body temperature, body weight gain, food and water intake were preserved under hyperthyroid conditions. In contrast, natural sex differences in heart rate disappeared with TH excess and deprivation. The variations of hyper- or hypothyroid traits of male and female mice were not explained by classical T3/T4 serum state. TH serum concentrations were significantly increased in female mice under hyperthyroidism, but no sex differences were found under eu- or hypothyroid conditions. Interestingly, analysis of expression of TH target genes and TH transporters revealed little sex dependency in heart, while sex differences in target genes were present in liver and brown adipose tissue in line with altered functional and metabolic traits of hyper- and hypothyroidism. CONCLUSIONS: These data demonstrate that the phenotypes of hypo- and hyperthyroidism differ between male and female mice and indicate that sex is an important modifier of phenotypic manifestations.

Accelerated progression of coronary artery calcification in hypertension but also prehypertension.

OBJECTIVE: To determine the role of hypertension for coronary artery calcification (CAC) progression. METHODS: The population-based Heinz Nixdorf Recall study recruited 4814 participants from a German urban population in 2000-2003. CAC was measured using electron-beam computed tomography at baseline and after 5 years. The present analyses refer to 3481 participants with repeat scan (coronary heart disease until 5 years excluded, age at baseline 45-74 years, and 53.1% women). Blood pressure (BP), Framingham risk factors, and antihypertensive medication were recorded at baseline. BP was staged according to Joint National Committee 7 guidelines. Participants under antihypertensive medication were classified as stage 2. CAC at 5 years was predicted from baseline using our dedicated, publicly available algorithm. CAC progression was accordingly classified as slow, expected, or rapid. RESULTS: Normotension was found in 20.5%, prehypertension in 27.2%, stage 1 hypertension in 15.8%, and stage 2 (ST2) in 36.5%. The frequency of rapid progression increases with BP stage (normotension: 16.7% to ST2: 21.1%, P = 0.004). Risk factor adjusted relative risk [RR (95% confidence interval), reference: normotension] of rapid progression was for prehypertension: 1.22 (0.98;1.51), stage 1: 1.29 (1.01;1.65), and ST2: 1.45 (1.17;1.79). Risk factor adjusted measures of CAC progression per 10 mmHg SBP were already elevated in women with BP below 140/90 mmHg: CAC onset, RR = 1.22 (1.07;1.40), rapid progression, RR = 1.17 (1.05;1.31), 5-year CAC progression, 6.7% (0.5;13.4). In men below 140/90 mmHg, only RR of rapid progression was considerably increased [RR = 1.11 (0.96;1.29)]. CONCLUSION: CAC progression, a sign of ongoing target organ damage, is already accelerated in prehypertensive patients, a substantial proportion of our urban population.

Associations among sleep disturbances, nocturnal sleep duration, daytime napping, and incident prediabetes and type 2 diabetes: the Heinz Nixdorf Recall Study.

OBJECTIVE: Poor sleep quality as well as short and long sleep duration has been linked to type 2 diabetes. In addition to confirmational analyses, we examined the impact of daytime napping on incident diabetes, and we assessed associations between sleep characteristics and incident prediabetes. METHODS: In a subgroup of the Heinz Nixdorf Recall Study, a population-based cohort study in Germany (N = 2962; age 45-75 years, without history of cancer, stroke, or cardiovascular diseases), diabetes at baseline and at 5-year follow-up was assessed by self-report and measurement of serum glucose levels. Prediabetes was defined as impaired fasting glucose (6.1-6.9 mmol/L). A sleep questionnaire was used to assess difficulties falling asleep, difficulties maintaining sleep, early morning arousal, and duration of nocturnal and daytime sleep. RESULTS: In adjusted regression models, short (≤5 hours) and long (≥7.5 hours) sleepers were at greater risk for diabetes (relative risk [RR] = 1.56, 95% confidence interval [CI] = 1.02-2.39, and 1.40, 95% CI = 1.01-1.96, respectively [reference: 7 hours]). Moreover, the prevalence of any regular sleep disorder was associated with incident diabetes (RR = 1.30, 95% CI = 1.01-1.68), and with incident prediabetes (RR = 1.31, 95% CI = 1.00-1.72). Regular daytime nappers had no increased risk of incident diabetes (RR = 1.00, 95% CI = 0.70-1.41). CONCLUSION: This study shows that people with regular sleep disorders, people with short and long sleep duration, but not regular daytime nappers are at increased risk of diabetes. Furthermore, regular sleep disorders are associated with an increased risk of prediabetes.

Mutant p97 exhibits species-specific changes of its ATPase activity and compromises the UBXD9-mediated monomerisation of p97 hexamers.

p97 (VCP) is a homo-hexameric triple-A ATPase that exerts a plethora of cellular processes. Heterozygous missense mutations of p97 cause at least five human neurodegenerative disorders. However, the specific molecular consequences of p97 mutations are hitherto widely unknown. Our in silico structural models of human and Dictyostelium p97 showed that the disease-causing human R93C, R155H, and R155C as well as Dictyostelium R154C, E219K, R154C/E219K p97 mutations constitute variations in surface-exposed locations. In-gel ATPase activity measurements of p97 monomers and hexamers revealed significant mutation- and species-specific differences. While all human p97 mutations led to an increase in ATPase activity, no changes could be detected for the Dictyostelium R154C mutant, which is orthologous to human R155C. The E219K mutation led to an almost complete loss of activity, which was partially recuperated in the R154C/E219K double-mutant indicating p97 inter-domain communication. By means of co-immunoprecipitation experiments we identified an UBX-domain containing Dictyostelium protein as a novel p97 interaction partner. We categorized all UBX-domain containing Dictyostelium proteins and named the interaction partner UBXD9. Pull-down assays and surface plasmon resonance analyses of Dictyostelium UBXD9 or the human orthologue TUG/ASPL/UBXD9 demonstrated direct interactions with p97 as well as species-, mutation- and ATP-dependent differences in the binding affinities. Sucrose density gradient assays revealed that both human and Dictyostelium UBXD9 proteins very efficiently disassembled wild-type, but to a lesser extent mutant p97 hexamers into monomers. Our results are consistent with a scenario in which p97 point mutations lead to differences in enzymatic activities and molecular interactions, which in the long-term result in a late-onset and progressive multisystem disease.

VCP and PSMF1: Antagonistic regulators of proteasome activity.

Protein turnover and quality control by the proteasome is of paramount importance for cell homeostasis. Dysfunction of the proteasome is associated with aging processes and human diseases such as neurodegeneration, cardiomyopathy, and cancer. The regulation, i.e. activation and inhibition of this fundamentally important protein degradation system, is still widely unexplored. We demonstrate here that the evolutionarily highly conserved type II triple-A ATPase VCP and the proteasome inhibitor PSMF1/PI31 interact directly, and antagonistically regulate proteasomal activity. Our data provide novel insights into the regulation of proteasomal activity.

The toxic effect of R350P mutant desmin in striated muscle of man and mouse.

Mutations of the human desmin gene on chromosome 2q35 cause autosomal dominant, autosomal recessive and sporadic forms of protein aggregation myopathies and cardiomyopathies. We generated R349P desmin knock-in mice, which harbor the ortholog of the most frequently occurring human desmin missense mutation R350P. These mice develop age-dependent desmin-positive protein aggregation pathology, skeletal muscle weakness, dilated cardiomyopathy, as well as cardiac arrhythmias and conduction defects. For the first time, we report the expression level and subcellular distribution of mutant versus wild-type desmin in our mouse model as well as in skeletal muscle specimens derived from human R350P desminopathies. Furthermore, we demonstrate that the missense-mutant desmin inflicts changes of the subcellular localization and turnover of desmin itself and of direct desmin-binding partners. Our findings unveil a novel principle of pathogenesis, in which not the presence of protein aggregates, but disruption of the extrasarcomeric intermediate filament network leads to increased mechanical vulnerability of muscle fibers. These structural defects elicited at the myofiber level finally impact the entire organ and subsequently cause myopathy and cardiomyopathy.

Heteromeric p97/p97R155C complexes induce dominant negative changes in wild-type and autophagy 9-deficient Dictyostelium strains.

Heterozygous mutations in the human VCP (p97) gene cause autosomal-dominant IBMPFD (inclusion body myopathy with early onset Paget's disease of bone and frontotemporal dementia), ALS14 (amyotrophic lateral sclerosis with or without frontotemporal dementia) and HSP (hereditary spastic paraplegia). Most prevalent is the R155C point mutation. We studied the function of p97 in the social amoeba Dictyostelium discoideum and have generated strains that ectopically express wild-type (p97) or mutant p97 (p97(R155C)) fused to RFP in AX2 wild-type and autophagy 9 knock-out (ATG9(KO)) cells. Native gel electrophoresis showed that both p97 and p97(R155C) assemble into hexamers. Co-immunoprecipitation studies revealed that endogenous p97 and p97(R155C)-RFP form heteromers. The mutant strains displayed changes in cell growth, phototaxis, development, proteasomal activity, ubiquitinylated proteins, and ATG8(LC3) indicating mis-regulation of multiple essential cellular processes. Additionally, immunofluorescence analysis revealed an increase of protein aggregates in ATG9(KO)/p97(R155C)-RFP and ATG9(KO) cells. They were positive for ubiquitin in both strains, however, solely immunoreactive for p97 in the ATG9(KO) mutant. A major finding is that the expression of p97(R155C)-RFP in the ATG9(KO) strain partially or fully rescued the pleiotropic phenotype. We also observed dose-dependent effects of p97 on several cellular processes. Based on findings in the single versus the double mutants we propose a novel mode of p97 interaction with the core autophagy protein ATG9 which is based on mutual inhibition.

Strumpellin is a novel valosin-containing protein binding partner linking hereditary spastic paraplegia to protein aggregation diseases.

Mutations of the human valosin-containing protein gene cause autosomal-dominant inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia. We identified strumpellin as a novel valosin-containing protein binding partner. Strumpellin mutations have been shown to cause hereditary spastic paraplegia. We demonstrate that strumpellin is a ubiquitously expressed protein present in cytosolic and endoplasmic reticulum cell fractions. Overexpression or ablation of wild-type strumpellin caused significantly reduced wound closure velocities in wound healing assays, whereas overexpression of the disease-causing strumpellin N471D mutant showed no functional effect. Strumpellin knockdown experiments in human neuroblastoma cells resulted in a dramatic reduction of axonal outgrowth. Knockdown studies in zebrafish revealed severe cardiac contractile dysfunction, tail curvature and impaired motility. The latter phenotype is due to a loss of central and peripheral motoneuron formation. These data imply a strumpellin loss-of-function pathogenesis in hereditary spastic paraplegia. In the human central nervous system strumpellin shows a presynaptic localization. We further identified strumpellin in pathological protein aggregates in inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia, various myofibrillar myopathies and in cortical neurons of a Huntington's disease mouse model. Beyond hereditary spastic paraplegia, our findings imply that mutant forms of strumpellin and valosin-containing protein may have a concerted pathogenic role in various protein aggregate diseases.

Proteasomal activity in skeletal muscle: a matter of assay design, muscle type, and age.

The ubiquitin-proteasome system (UPS) is a major degradation system for regulatory and misfolded proteins. UPS function has been implicated to exert a central role in the pathogenesis of various human diseases. Because biochemical analyses are often hampered by the amount of available diseased tissue, we report on the establishment and validation of a luminescence-based proteasomal activity assay applicable to 5-mg quantities of skeletal muscle. We demonstrate that the specific proteasomal activity differs in individual muscle groups and decreases with aging. These findings warrant the use of appropriate controls and a careful interpretation of results in mammalian skeletal muscle pathologies.