The endocrine role of the skeleton: background and clinical evidence

Based on the observation that diabetes, obesity, and hypogonadism influence bone metabolism, the existence of a feedback loop and a common regulation was postulated and an endocrine role ascribed to the skeleton. In the first part of this review, two pathways are described whereby adipose tissue acts on bone mass. In the first, leptin activates the sympathetic nervous system via serotonin and diminishes bone mass accrual. The second pathway functions via the activation of CART (CARTPT) and inhibits bone resorption. The first pathway leads to a decrease in bioactivity of the osteoblast-produced hormone osteocalcin (OC) (part 2). In its undercarboxylated form, OC acts on the three targets pancreas, adipose tissue, and gonads (part 3) and thereby causes an increase in insulin secretion and sensitivity, β-cell proliferation, and male fertility. Insulin (part 4) is part of a recently discovered regulatory feedback loop between pancreas and osteoblasts. It is a strong counterplayer of leptin as it causes a decrease in OPG expression and enhances bone resorption and OC decarboxylation. Numerous clinical studies (part 5) have shown associations of total and undercarboxylated OC and markers of energy metabolism. Interventional studies, to date only performed in murine models, have shown positive effects of OC administration on energy metabolism. Whether bone tissue has an even further-reaching endocrine role remains to be elucidated.     

The Bcl-2 protein family and its role in the development of neoplastic disease

Programmed cell death is the physiological process responsible for shaping organs during embryogenesis, maintaining tissue homeostasis and allowing controlled deletion of potentially harmful cells within the adult organism. The genetics of apoptosis are well conserved in all metazoans and although the evolution of humans and worms separated more than 600 million years ago, basic signaling concepts in apoptosis are highly related in both species. More crucial to humans than worms is the fact that abnormalities in cell death control can contribute to the development of cancer. While C.elegans can easily survive with additional somatic cells that should normally be deleted during development humans may suffer pathological consequences, ranging from tumorigenesis to autoimmunity, as a result of mutations in cell death regulatory genes. Despite the high degree of evolutionary conservation in cell death control, apoptosis signaling in mammals is much more complex than in C.elegans. In mammalian cells, programmed cell death can be induced either by ligand-mediated activation of certain members of the tumor necrosis factor receptor family--so-called 'death receptors'--such as Fas (CD95/Apo-1) and TRAIL or it can be induced in a cell autonomous manner in response to certain stress signals by pro-apoptotic members of the Bcl-2 family. In this review, we focus on general concepts of how the Bcl-2 protein family regulates cell death and how deregulation of this 'intrinsic' apoptotic signaling pathway impinges on the pathogenesis of malignant disease, the major cause of death in the aging population.     

Hypofibrinolysis in type 2 diabetes: the role of the inflammatory pathway and complement C3

Aims/hypothesis

Plasminogen activator inhibitor-1 (PAI-1) has been regarded as the main antifibrinolytic protein in diabetes, but recent work indicates that complement C3 (C3), an inflammatory protein, directly compromises fibrinolysis in type 1 diabetes. The aim of the current project was to investigate associations between C3 and fibrinolysis in a large cohort of individuals with type 2 diabetes.

Methods

Plasma levels of C3, C-reactive protein (CRP), PAI-1 and fibrinogen were analysed by ELISA in 837 patients enrolled in the Edinburgh Type 2 Diabetes Study. Fibrin clot lysis was analysed using a validated turbidimetric assay.

Results

Clot lysis time correlated with C3 and PAI-1 plasma levels (r?=?0.24, p?<?0.001 and r?=?0.22, p?<?0.001, respectively). In a multivariable regression model involving age, sex, BMI, C3, PAI-1, CRP and fibrinogen, and using log-transformed data as appropriate, C3 was associated with clot lysis time (regression coefficient 0.227 [95% CI 0.161, 0.292], p?<?0.001), as was PAI-1 (regression coefficient 0.033 [95% CI 0.020, 0.064], p?<?0.05) but not fibrinogen (regression coefficient 0.003 [95% CI ?0.046, 0.051], p?=?0.92) or CRP (regression coefficient 0.024 [95% CI ?0.008, 0.056], p?=?0.14). No correlation was demonstrated between plasma levels of C3 and PAI-1 (r?=??0.03, p?=?0.44), consistent with previous observations that the two proteins affect different pathways in the fibrinolytic system.

Conclusions/interpretation

Similarly to PAI-1, C3 plasma levels are independently associated with fibrin clot lysis in individuals with type 2 diabetes. Therefore, future studies should analyse C3 plasma levels as a surrogate marker of fibrinolysis potential in this population.     

Estimated trends in the prevalence of heroin addiction in Switzerland. A multiple-indicator approach

Data on the prevalence of heroin addiction have considerable relevance in the field of public health as a means of evaluating measures aimed at improving the lives of the individuals concerned. The number of heroin addicts in Switzerland was estimated by six different methods based on various data sources. This resulted in an overall estimate for the reference year 1997 ranging from a minimum of 24,000 to a maximum of 35,000 heroin addicts. In the 1990s, the trend in the prevalence of heroin addiction was characterised by a rapid rise up to 1993/94 followed by a gradual decline. The increasing medicalisation (focus on treatment rather than on punishment) of Switzerland's heroin problem has therefore not translated into a clear downward trend in the estimated prevalence of heroin addiction; however, the data for the various sub-groups lend plausibility to the assumption that this population is more integrated, less conspicuous and receiving better medical care.     

Virus-induced over-expression of protein phosphatase 2A inhibits insulin signalling in chronic hepatitis C

BACKGROUND/AIMS: Hepatitis C virus (HCV) infection disturbs glucose and lipid metabolism contributing to the development of liver steatosis, insulin resistance and type 2 diabetes mellitus. On the other hand, insulin resistance and steatosis have been found to be associated with increased rates of fibrosis progression and lower rates of response to interferon therapy in chronic hepatitis C (CHC). The molecular mechanisms contributing to insulin resistance in CHC are not well understood. We have shown previously that protein phosphatase 2A (PP2A) is over-expressed in biopsies from patients with CHC. In this study, we tested if PP2A over-expression leads to insulin resistance. METHODS: We studied insulin signalling in cell lines that allow the regulated over-expression of HCV proteins and of the PP2A catalytic subunit (PP2Ac). Insulin signalling and PP2Ac expression were also studied in HCV transgenic mice and in liver biopsies from patients with CHC. RESULTS: Over-expression of PP2Ac in cells inhibited insulin signalling by dephosphorylation of PKB/Akt. PP2Ac over-expression and impaired insulin signalling were found in the liver of HCV transgenic mice and in liver biopsies of patients with CHC. CONCLUSIONS: HCV-induced over-expression of PP2A in the liver contributes to the pathogenesis of insulin resistance in patients with CHC.     

The hsp27kD heat shock protein and p38-MAPK signaling are required for regular epidermal differentiation

Background

In human epidermal keratinocytes the expression of hsp27 is closely related to differentiation in vitro and in situ.

Objective

We aimed to gain further insight into the role of hsp27 in epidermal differentiation by specific inhibition through siRNA and inhibition of p38-MAPK, the key enzyme of hsp27 phosphorylation.

Methods

Normal human keratinocytes (KC) and organotypic skin cultures (SE-skin equivalents) were used. Expression and phosphorylation of hsp27 was inhibited in these models by siRNA and SB203580, a specific inhibitor of p38-MAPK, respectively. Modification of morphology and expression of hsp27 and other differentiation associated proteins was investigated by immunofluorescence, western blot, and RT-PCR.

Results

Inhibition of p38-MAPK resulted in a downregulation of hsp27 in KC and SE. Additionally, in the presence of SB203580 Ca²⁺ induced expression of pro-filaggrin and loricrin was inhibited at the protein level and expression of filaggrin, keratin 10, and transglutaminase 1 at the mRNA level. Addition of SB203580 to SE, as well as hsp27 knockdown in this model resulted in identical patterns of irregular differentiation, disturbance of epidermal layers, and delayed expression of K10.

Conclusion

These results provide evidence that the expression of hsp27 and its phosphorylation by p38-MAPK are required for keratinocyte differentiation and for the formation of a regularly stratified epidermis.     

A mitochondrial myopathy in an infant with lactic acidosis

We describe a girl with mitochondrial myopathy, who presented with general muscle weakness, muscle hypotonia and motor retardation. The level of blood lactate and pyruvate was consistently increased. Enzymatic studies showed impairment of NADH-dehydrogenase activity (complex I of the respiratory chain) in skeletal muscle. Electron-microscopy of a muscle biopsy showed abnormalities of a mitochondrial myopathy. The girl, now aged 30 months, has been treated with riboflavine (vitamin B2) since the age of 14 months, and lactate and pyruvate levels have decreased to normal. The patient still shows mild muscle hypotonia and weakness, but good motor progress and normal cognitive development.     

Selective increase of in vivo firing frequencies in DA SN neurons after proteasome inhibition in the ventral midbrain

The impairment of protein degradation via the ubiquitin‐proteasome system (UPS) is present in sporadic Parkinson's disease (PD), and might play a key role in selective degeneration of vulnerable dopamine (DA) neurons in the substantia nigra pars compacta (SN). Further evidence for a causal role of dysfunctional UPS in familial PD comes from mutations in parkin, which results in a loss of function of an E3‐ubiquitin‐ligase. In a mouse model, genetic inactivation of an essential component of the 26S proteasome lead to widespread neuronal degeneration including DA midbrain neurons and the formation of alpha‐synuclein‐positive inclusion bodies, another hallmark of PD. Studies using pharmacological UPS inhibition in vivo had more mixed results, varying from extensive degeneration to no loss of DA SN neurons. However, it is currently unknown whether UPS impairment will affect the neurophysiological functions of DA midbrain neurons. To answer this question, we infused a selective proteasome inhibitor into the ventral midbrain in vivo and recorded single DA midbrain neurons 2 weeks after the proteasome challenge. We found a selective increase in the mean in vivo firing frequencies of identified DA SN neurons in anesthetized mice, while those in the ventral tegmental area (VTA) were unaffected. Our results demonstrate that a single‐hit UPS inhibition is sufficient to induce a stable and selective hyperexcitability phenotype in surviving DA SN neurons in vivo. This might imply that UPS dysfunction sensitizes DA SN neurons by enhancing ‘stressful pacemaking’.