Eoin J. Cotter

Mechanism of HIV protein induced modulation of mesenchymal stem cell osteogenic differentiation

BackgroundA high incidence of decreased bone mineral density (BMD) has been associated with HIV infection. Normal skeletal homeostasis is controlled, at least in part, by the maturation and activity of mature osteoblasts. Previous studies by our group have demonstrated the ability of HIV proteins to perturb osteoblast function, and the degree of osteogenesis in differentiating mesenchymal stem cells (MSCs). This study attempts to further dissect the dynamics of this effect.MethodsMSCs were cultured under both osteogenic (cultured in commercially available differentiation media) and quiescent (cultured in basal medium) conditions. Both cell populations were exposed to HIV p55-gag and HIV rev (100 ng/ml). Time points were taken at 3, 6, 9, and 15 days for osteogenic conditions, while quiescent cells were treated for 1 week. Cell function (alkaline phosphatase [ALP] activity, calcium deposition, and lipid levels) and the activity of the key MSC transcription factors, RUNX-2 and PPARgamma were determined post-exposure. Also, in cells cultured in differentiating conditions, cellular levels of connective tissue growth factor (CTGF) were analysed using whole cell ELISA, while BMP-2 secretion was also examined.ResultsIn differentiating MSCs, exposure to HIV proteins caused significant changes in both the timing and magnitude of key osteogenic events and signals. Treatment with REV increased the overall rate of mineralization, and induced earlier increases in CTGF levels, RUNX-2 activity and BMP-2 secretion, than those observed in the normal course of differntiation. In contrast, p55-gag reduced the overall level of osteogenesis, and reduced BMP-2 secretion, RUNX-2 activity, CTGF levels and ALP activity at many of the timepoints examined. Finally, in cells cultured in basal conditions, treatment with HIV proteins did not in and of itself induce a significant degree of differentiation over the time period examined.ConclusionThese data demonstrate that the effect of HIV proteins on bone is dependent on the differentiation status of the cells that they are in contact with. The effect on bone cell signalling provides insights into the mechanism of HIV induced decreases in bone mineral density.

HIV Type 1 Alters Mesenchymal Stem Cell Differentiation Potential and Cell Phenotype ex Vivo

An increased incidence of bone and lipid toxicities is associated with HIV-1 infection and its treatment. Mesenchymal stem cells (MSCs) are multipotent cells that can differentiate into both osteoblasts (OB) and adipocytes (AC). We hypothesize that the interaction of MSC and HIV-1 underlie these toxicities. Serum was collected from uninfected control and HIV-infected, antiviral-naive patients. Sera were divided into three groups: HIV-negative sera (n = 5), HIV-positive low viral load (LVL) (VL range 120; 4000, n = 5) or high viral load (HVL) (VL range 100,000; 500,000, n = 5). MSCs were exposed to these sera (5%) in an adipogenic/osteogenic condition and in nondifferentiating conditions in acute and chronic exposure models. Markers of adipogenesis/osteogenesis were examined in both MSCs induced to differentiated and nondifferentiating cells. Sera from HVL HIV-1-infected individuals induced a clear proadipogenic phenotype, as evidenced by an increase in adipocyte formation and the induction of increased expression of adipogenic markers including LPL and PPARγ. Both CD4 receptor blockade and treatment with the antiretroviral AZT attenuated these proadipogenic effects, suggesting that an infection event may underlie the observed phenomena. Finally, inhibition of COUP TF-1 by HIV-1 TAT was identified as a potential molecular mechanism for these effects. These results suggest that HIV-1 directly interacts with and may infect MSCs resulting in alterations of their differentiation potential, findings that significantly enhance our understanding of HIV-1-associated bone and fat toxicities.

Novel Roles of Neuropeptide Processing Enzymes: EC3.4.24.15 in the Neurome

Neuropeptide processing metalloenzymes, such as angiotensin converting enzyme, neprilysin, endothelin converting enzyme, neurolysin, and EC3.4.24.15 (EP24.15), are central to the formation and degradation of bioactive peptides. We present EP24.15 as a paradigm for novel functions ascribed to these enzymes in the neurome. Although the neurome typically encompasses proteomes of the brain and central nervous system, exciting new roles of these neuropeptidases have been demonstrated in other organ systems. We discuss the involvement of EP24.15 with clinical sequelae involving the use of gonadotropin‐releasing hormone (GnRH; LHRH) analogs that act as enzyme inhibitors, in vascular physiology (blood pressure regulation), and in the hematologic system (immune surveillance). Hemodynamic forces, such as cyclic strain and shear stress, on vascular cells, induce an increase in EP24.15 transcription, suggesting that neuropeptidase‐mediated hydrolysis of pressor/depressor peptides is likely regulated by changes in hemodynamic force and blood pressure. Lastly, EP24.15 regulates surface expression of major histocompatibility complex Class I proteins in vivo, suggesting that EP24.15 may play an important role in maintenance of immune privilege in sites of increased endogenous expression. In these extraneural systems, regulation of both neuropeptide and other peptide substrates by neuropeptidases indicates that the influence of these enzymes may be more global than was anticipated previously, and suggests that their attributed role as neuropeptidases underestimates their physiologic actions in the neural system.

Systemic gene dysregulation in classical Galactosaemia: Is there a central mechanism?

Classical Galactosaemia is a rare disorder of carbohydrate metabolism caused by a deficiency of galactose-1-phosphate uridyltransferase (GALT). The disease is life-threatening in the neonate, and the only treatment option is life-long dietary restriction of galactose. However, long-term complications persist in treated patients including cognitive impairments, speech and language abnormalities and premature ovarian insufficiency in females. Microarray analysis of T-lymphocytes from treated adult patients identified systemic dysregulation of numerous gene pathways, including the glycosylation, inflammatory and inositol pathways. Analysis of gene expression in patient-derived dermal fibroblasts of patients exposed to toxic levels of galactose, with immunostaining, has further identified the susceptibility of the glycosylation gene alpha-1,2-mannosyltransferase (ALG9) and the inflammatory gene annexin A1 (ANXA1) to increased galactose concentrations. These data suggest that Galactosaemia is a multi-system disorder affecting numerous signalling pathways.

Is PPARγ a prospective player in HIV-1-associated bone disease?

Currently infection with the human immunodeficiency virus-1 (HIV-1) is in most instances a chronic disease that can be controlled by effective antiretroviral therapy (ART). However, chronic use of ART has been associated with a number of toxicities; including significant reductions in bone mineral density (BMD) and disorders of the fat metabolism. The peroxisome proliferator-activated receptor gamma (PPARγ) transcription factor is vital for the development and maintenance of mature and developing adipocytes. Alterations in PPARγ expression have been implicated as a factor in the mechanism of HIV-1-associated lipodystrophy. Both reduced BMD and lipodystrophy have been well described as complications of HIV-1 infection and treatment, and a question remains as to their interdependence. Interestingly, both adipocytes and osteoblasts are derived from a common precursor cell type; the mesenchymal stem cell. The possibility that dysregulation of PPARγ (and the subsequent effect on both osteoblastogenesis and adipogenesis) is a contributory factor in the lipid- and bone-abnormalities observed in HIV-1 infection and treatment has also been investigated. This review deals with the hypothesis that dysregulation of PPARγ may underpin the bone abnormalities associated with HIV-1 infection, and treats the current knowledge and prospective developments, in our understanding of PPARγ involvement in HIV-1-associated bone disease.

Regulation of Endopeptidases EC3.4.24.15 and EC3.4.24.16 in Vascular Endothelial Cells by Cyclic Strain: Role of Gi Protein Signaling

Objective—Endopeptidase EC3.4.24.15 (EP24.15)- and EC3.4.24.16 (EP24.16)-specific peptide hydrolysis plays an important role in endothelium-mediated vasoregulation. Given the significant influence of hemodynamic forces on vascular homeostasis and pathology, we postulated that these related peptidases may be mechanosensitive. The objective of this study, therefore, was to investigate the putative role of cyclic strain in regulating the expression and enzymatic activity of EP24.15 and EP24.16 in bovine aortic endothelial cells (BAECs). Methods and Results—BAECs were cultured under conditions of defined cyclic strain (0% to 10% stretch, 60 cycles/min, 0 to 24 hours). Strain significantly increased EP24.15 and EP24.16 soluble activity in a force- and time-dependent manner, with elevations of 2.3±0.4- and 1.9±0.3-fold for EP24.15 and EP24.16, respectively, after 24 hours at 10% strain. Pharmacological agents and dominant-negative G protein mutants used to selectively disrupt Gi&agr;- and G&bgr;&ggr;-mediated signaling pathways attenuated strain-dependent (24 hours, 5%) increases for both enzymes. Differences in the inhibitory profile for both enzymes were also noted, with EP24.15 displaying greater sensitivity to Gi&agr;2/3 inhibition and EP24.16 exhibiting greater sensitivity to Gi&agr;1/2 and G&bgr;&ggr; inhibition. Cyclic strain also increased levels of secreted EP24.15 and EP24.16 activity by 2.6±0.02- and 3.6±0.2-fold, respectively, in addition to mRNA levels for both enzymes (EP24.15 +42%, EP24.16 +56%). Conclusions—Our findings suggest that cyclic strain putatively regulates both the mRNA expression and enzymatic function of EP24.15 and EP24.16 in BAECs via alternate Gi protein signaling pathways.

HEMODYNAMIC REGULATION OF METALLOPEPTIDASES WITHIN THE VASCULATURE

Hemodynamic forces associated with blood flow play a vital role in the endothelial regulation of vascular tone, remodeling and the initiation and progression of vascular diseases such as atherosclerosis and hypertension. Crucial elements in endothelium-mediated events within the blood vessel are bioactive peptide signals and their associated hydrolytic enzymes. This review examines the relationship between hemodynamic forces such as shear stress and cyclic strain, and an important group of peptide-degrading enzymes within the endothelium, the thermolysin-like zinc metallopeptidases.

Expression of neuroepithelial transforming gene 1 is enhanced in oesophageal cancer and mediates an invasive tumour cell phenotype

IntroductionNeuroepithelial Transforming Gene 1 (NET1) is a well characterised oncoprotein and a proven marker of an aggressive phenotype in a number of cancers, including gastric adenocarcinoma. We aimed to investigate whether NET1 plays a functional role in oesophageal cancer (OAC) and its pre-malignant phenotype Barrett’s oesophagus.MethodsBaseline NET1 mRNA levels were determined by qPCR across a panel of six cell lines, including normal oesophageal, Barrett’s and OAC derived cells. Quantification of NET1 protein in OAC cells was performed using Western blot and immunofluorescence. NET1 expression was modulated by treating with lysophosphatidic acid (LPA) and NET1-specific siRNA. The functional effects of NET1 knockdown were assessed in vitro using proliferation, migration and invasion assays.ResultsNET1 expression was increased in Barrett’s and in OAC-derived cells in comparison to normal oesophageal cells. The highest expression was observed in OE33 a Barrett’s-related OAC cell line. NET1 protein and mRNA expression was enhanced by LPA treatment in OAC and furthermore LPA treatment caused increased proliferation, migration and invasion in a NET1-dependent manner. NET1 knockdown resulted in reduced OAC cell proliferation and invasion.ConclusionsAs found in other malignancies, NET1 expression is elevated in OAC and its pre-malignant phenotype, Barrett’s oesophagus. NET1 promotes OAC cell invasion and proliferation and it mediates LPA-induced OAC cell migration.

Progenitor Cell Types in HIV-1 Infection: Bioactivity and Emerging Targets for Treatment

HIV-1 exerts its most profound effects through destruction of the hosts immune responses specifically through targeting of the T-lymphocyte populations. In addition to its primary immune target, HIV-1 also targets cells of the nervous, skeletal and vascular system. There is emerging evidence to suggest that HIV-1 may, in part at least, affect these diverse tissues by impairing the homeostatic production of terminally differentiated cells from stem and progenitor cell populations. The interaction between HIV-1 and stem cell populations may serve to underpin the diverse non-immunological effects of HIV-1. This review deals with the effect of HIV-1 infection on a number of progenitor cell types, with emphasis on delineating mechanisms of HIVs destructive effect on the body. Modification of these effects may represent novel avenues for exploration in our search for clinical interventions.

Role of Mesenchymal Stem Cells (MSC) in HIV-1 Associated Bone and Lipid Toxicities

In addition to its well-recognised impact on the immune system, HIV-1 infection has long been associated with disorders of other tissue types, and with the advent of long term anti-retroviral therapy specific toxicities of both bone and lipid tissues have emerged. These issues are of significant clinical importance in a population receiving life-time therapy. The mechanisms underpinning these toxicities have yet to be fully understood, and the relative contribution of virus and treatment (especially in the case of bone toxicities) fully elucidated.