Continuous parathyroid hormone induces cortical porosity in the rat: effects on bone turnover and mechanical properties.

We examined the time course effects of continuous PTH on cortical bone and mechanical properties. PTH increased cortical bone turnover and induced intracortical porosity with no deleterious effect on bone strength. Withdrawal of PTH increased maximum torque to failure and stiffness with no change in energy absorbed. INTRODUCTION: The skeletal response of cortical bone to parathyroid hormone (PTH) is complex and species dependent. Intermittent administration of PTH to rats increases periosteal and endocortical bone formation but has no known effects on intracortical bone turnover. The effects of continuous PTH on cortical bone are not clearly established. MATERIALS AND METHODS: Eighty-four 6-month-old female Sprague-Dawley rats were divided into three control, six PTH, and two PTH withdrawal (WD) groups. They were subcutaneously implanted with osmotic pumps loaded with vehicle or 40 microg/kg BW/day human PTH(1-34) for 1, 3, 5, 7, 14, and 28 days. After 7 days, PTH was withdrawn from two groups of animals for 7 (7d-PTH/7d-WD) and 21 days (7d-PTH/21d-WD). Histomorphometry was performed on periosteal and endocortical surfaces of the tibial diaphysis in all groups. microCT of tibias and mechanical testing by torsion of femora were performed on 28d-PTH and 7d-PTH/21d-WD animals. RESULTS AND CONCLUSIONS: Continuous PTH increased periosteal and endocortical bone formation, endocortical osteoclast perimeter, and cortical porosity in a time-dependent manner, but did not change the mechanical properties of the femur, possibly because of addition of new bone onto periosteal and endocortical surfaces. Additionally, withdrawal of PTH restored normal cortical porosity and increased maximum torque to failure and stiffness. We conclude that continuous administration of PTH increased cortical porosity in rats without having a detrimental effect on bone mechanical properties.     

Genetic contributions to Parkinson's disease

Sporadic Parkinson's disease (PD) is a common neurodegenerative disorder, characterized by the loss of midbrain dopamine neurons and Lewy body inclusions. It is thought to result from a complex interaction between multiple predisposing genes and environmental influences, although these interactions are still poorly understood. Several causative genes have been identified in different families. Mutations in two genes [α-synuclein and nuclear receptor-related 1 (Nurr1)] cause the same pathology, and a third locus on chromosome 2 also causes this pathology. Other familial PD mutations have identified genes involved in the ubiquitin–proteasome system [parkin and ubiquitin C-terminal hydroxylase L1 (UCHL1)], although such cases do not produce Lewy bodies. These studies highlight critical cellular proteins and mechanisms for dopamine neuron survival as disrupted in Parkinson's disease. Understanding the genetic variations impacting on dopamine neurons may illuminate other molecular mechanisms involved. Additional candidate genes involved in dopamine cell survival, dopamine synthesis, metabolism and function, energy supply, oxidative stress, and cellular detoxification have been indicated by transgenic animal models and/or screened in human populations with differing results. Genetic variation in genes known to produce different patterns and types of neurodegeneration that may impact on the function of dopamine neurons are also reviewed. These studies suggest that environment and genetic background are likely to have a significant influence on susceptibility to Parkinson's disease. The identification of multiple genes predisposing to Parkinson's disease will assist in determining the cellular pathway/s leading to the neurodegeneration observed in this disease.     

Tau isoform expression in frontotemporal dementia without tau deposition

In many cases of sporadic frontotemporal dementia (FTD) and in FTD caused by tau mutations (FTDP-17) there is disruption of the normal splicing of tau leading to the aberrant expression of tau isoforms and neurodegeneration. This suggests a central role for tau in the pathogenesis of FTD. However, more than half the cases of sporadic FTD show no tau deposition. We question whether altered expression is also involved in the pathogenesis of tau-negative FTD. Real-time polymerase chain reaction was used to investigate tau isoform expression in tau-negative FTD and age-matched controls. There were no differences in total tau mRNA or 4R versus 3R isoform expression. Our study suggests that perturbed tau mRNA expression is unlikely to be involved in the pathogenesis of tau-negative FTD.     

In vivo and in vitro models demonstrate a role for caveolin-1 in the pathogenesis of ischaemic acute renal failure

Caveolae and their proteins, the caveolins, transport macromolecules; compartmentalize signalling molecules; and are involved in various repair processes. There is little information regarding their role in the pathogenesis of significant renal syndromes such as acute renal failure (ARF). In this study, an in vivo rat model of 30 min bilateral renal ischaemia followed by reperfusion times from 4 h to 1 week was used to map the temporal and spatial association between caveolin-1 and tubular epithelial damage (desquamation, apoptosis, necrosis). An in vitro model of ischaemic ARF was also studied, where cultured renal tubular epithelial cells or arterial endothelial cells were subjected to injury initiators modelled on ischaemia-reperfusion (hypoxia, serum deprivation, free radical damage or hypoxia-hyperoxia). Expression of caveolin proteins was investigated using immunohistochemistry, immunoelectron microscopy, and immunoblots of whole cell, membrane or cytosol protein extracts. In vivo, healthy kidney had abundant caveolin-1 in vascular endothelial cells and also some expression in membrane surfaces of distal tubular epithelium. In the kidneys of ARF animals, punctate cytoplasmic localization of caveolin-1 was identified, with high intensity expression in injured proximal tubules that were losing basement membrane adhesion or were apoptotic, 24 h to 4 days after ischaemia-reperfusion. Western immunoblots indicated a marked increase in caveolin-1 expression in the cortex where some proximal tubular injury was located. In vitro, the main treatment-induced change in both cell types was translocation of caveolin-1 from the original plasma membrane site into membrane-associated sites in the cytoplasm. Overall, expression levels did not alter for whole cell extracts and the protein remained membrane-bound, as indicated by cell fractionation analyses. Caveolin-1 was also found to localize intensely within apoptotic cells. The results are indicative of a role for caveolin-1 in ARF-induced renal injury. Whether it functions for cell repair or death remains to be elucidated.     

Detection and genotyping of oocysts of Cryptosporidium parvum by real-time PCR and melting curve analysis

Several real-time PCR procedures for the detection and genotyping of oocysts of Cryptosporidium parvum were evaluated. A 40-cycle amplification of a 157-bp fragment from the C. parvum beta-tubulin gene detected individual oocysts which were introduced into the reaction mixture by micromanipulation. SYBR Green I melting curve analysis was used to confirm the specificity of the method when DNA extracted from fecal samples spiked with oocysts was analyzed. Because C. parvum isolates infecting humans comprise two distinct genotypes, designated type 1 and type 2, real-time PCR methods for discriminating C. parvum genotypes were developed. The first method used the same beta-tubulin amplification primers and two fluorescently labeled antisense oligonucleotide probes spanning a 49-bp polymorphic sequence diagnostic for C. parvum type 1 and type 2. The second genotyping method used SYBR Green I fluorescence and targeted a polymorphic coding region within the GP900/poly(T) gene. Both methods discriminated between type 1 and type 2 C. parvum on the basis of melting curve analysis. To our knowledge, this is the first report describing the application of melting curve analysis for genotyping of C. parvum oocysts.     

Detection of human perforin by ELISpot and ELISA: ex vivo identification of virus-specific cells

The perforin (PFN) protein is essential for the elimination of target cells by cytotoxic T lymphocytes (CTL) and natural killer (NK) cells. The study of cells releasing PFN has been hampered by a lack of sensitive methods. We therefore produced PFN-reactive monoclonal antibodies (mAb) and developed capture enzyme-linked immunosorbent (ELISA) and enzyme-linked immunospot (ELISpot) assays. Three mAbs were generated and shown to react with unique determinants of PFN. All mAbs recognized intracellular PFN in human peripheral blood mononuclear cell (PBMC) as assessed by flow cytometry and immunohistochemistry. Functional PFN capture ELISA and ELISpot assays were developed utilizing two of the mAbs for capture and the third mAb for detection. When examining PFN release by the YT lymphoma cell line, the ELISpot displayed a greater detection sensitivity than the ELISA. Assessment of PFN release by a CTL clone using ELISpot gave results consistent with a parallel (51)Cr-release cytotoxicity assay. Moreover, PFN release by PBMC could be quantified by ELISpot and ELISA after ex vivo stimulation with defined CTL epitopes from common viruses. These novel immunoassays will be valuable for further investigations of the mechanisms underlying granule-mediated apoptosis. In addition, the capture immunoassays could provide tools for studying CTL responses in infectious and tumor diseases as well as for vaccine development.     

Stress resistance as a determinate of C. elegans lifespan

It is difficult to exaggerate the progress that has been made in biogerontology over the last 15 years. As with all scientific revolutions, a few experiments in a small number of laboratories have changed the way in which we think about and design experiments. As a result of these experiments, there is much evidence to suggest that a rudimentary understanding of some of the processes that cause aging will be available in the next decade. One particular area of progress is the molecular genetics of lifespan. Although one may draw some distinctions between chronological lifespan and normal aging, extended lifespan remains one of the best indicators that an intervention in an aging process has been made. The isolation of a long-lived variant of a laboratory invertebrate is now essentially a trivial project but the information obtained from this approach is proving invaluable. As with most other biological problems, the most important experimental developments are coming from studying simple organisms in a reductionist fashion.