Axonal response of mitochondria to demyelination and complex IV activity within demyelinated axons in experimental models of multiple sclerosis

AIMS

Axonal injury in multiple sclerosis (MS) and experimental models is most frequently detected in acutely demyelinating lesions. We recently reported a compensatory neuronal response, where mitochondria move to the acutely demyelinated axon and increase the mitochondrial content following lysolecithin-induced demyelination. We termed this homeostatic phenomenon, which is also evident in MS, the axonal response of mitochondria to demyelination (ARMD). The aim of this study is to determine whether ARMD is consistently evident in experimental demyelination and how its perturbation relates to axonal injury.

METHODS

In the present study, we assessed axonal mitochondrial content as well as axonal mitochondrial respiratory chain complex IV activity (cytochrome c oxidase or COX) of axons and related these to axonal injury in nine different experimental disease models. We used immunofluorescent histochemistry as well as sequential COX histochemistry followed by immunofluorescent labelling of mitochondria and axons.

RESULTS

We found ARMD a consistent and robust phenomenon in all experimental disease models. The increase in mitochondrial content within demyelinated axons, however, was not always accompanied by a proportionate increase in complex IV activity, particularly in highly inflammatory models such as experimental autoimmune encephalomyelitis (EAE). Axonal complex IV activity inversely correlated with the extent of axonal injury in experimental disease models.

CONCLUSIONS

Our findings indicate that ARMD is a consistent and prominent feature and emphasise the importance of complex IV activity in the context of ARMD, especially in autoimmune inflammatory demyelination, paving the way for the development of novel neuroprotective therapies.

Enhanced axonal response of mitochondria to demyelination offers neuroprotection: implications for multiple sclerosis

Axonal loss is the key pathological substrate of neurological disability in demyelinating disorders, including multiple sclerosis (MS). However, the consequences of demyelination on neuronal and axonal biology are poorly understood. The abundance of mitochondria in demyelinated axons in MS raises the possibility that increased mitochondrial content serves as a compensatory response to demyelination. Here, we show that upon demyelination mitochondria move from the neuronal cell body to the demyelinated axon, increasing axonal mitochondrial content, which we term the axonal response of mitochondria to demyelination (ARMD). However, following demyelination axons degenerate before the homeostatic ARMD reaches its peak. Enhancement of ARMD, by targeting mitochondrial biogenesis and mitochondrial transport from the cell body to axon, protects acutely demyelinated axons from degeneration. To determine the relevance of ARMD to disease state, we examined MS autopsy tissue and found a positive correlation between mitochondrial content in demyelinated dorsal column axons and cytochrome c oxidase (complex IV) deficiency in dorsal root ganglia (DRG) neuronal cell bodies. We experimentally demyelinated DRG neuron-specific complex IV deficient mice, as established disease models do not recapitulate complex IV deficiency in neurons, and found that these mice are able to demonstrate ARMD, despite the mitochondrial perturbation. Enhancement of mitochondrial dynamics in complex IV deficient neurons protects the axon upon demyelination. Consequently, increased mobilisation of mitochondria from the neuronal cell body to the axon is a novel neuroprotective strategy for the vulnerable, acutely demyelinated axon. We propose that promoting ARMD is likely to be a crucial preceding step for implementing potential regenerative strategies for demyelinating disorders.

Teriflunomide treatment for multiple sclerosis modulates T cell mitochondrial respiration with affinity-dependent effects

Interference with immune cell proliferation represents a successful treatment strategy in T cell-mediated autoimmune diseases such as rheumatoid arthritis and multiple sclerosis (MS). One prominent example is pharmacological inhibition of dihydroorotate dehydrogenase (DHODH), which mediates de novo pyrimidine synthesis in actively proliferating T and B lymphocytes. Within the TERIDYNAMIC clinical study, we observed that the DHODH inhibitor teriflunomide caused selective changes in T cell subset composition and T cell receptor repertoire diversity in patients with relapsing-remitting MS (RRMS). In a preclinical antigen-specific setup, DHODH inhibition preferentially suppressed the proliferation of high-affinity T cells. Mechanistically, DHODH inhibition interferes with oxidative phosphorylation (OXPHOS) and aerobic glycolysis in activated T cells via functional inhibition of complex III of the respiratory chain. The affinity-dependent effects of DHODH inhibition were closely linked to differences in T cell metabolism. High-affinity T cells preferentially use OXPHOS during early activation, which explains their increased susceptibility toward DHODH inhibition. In a mouse model of MS, DHODH inhibitory treatment resulted in preferential inhibition of high-affinity autoreactive T cell clones. Compared to T cells from healthy controls, T cells from patients with RRMS exhibited increased OXPHOS and glycolysis, which were reduced with teriflunomide treatment. Together, these data point to a mechanism of action where DHODH inhibition corrects metabolic disturbances in T cells, which primarily affects profoundly metabolically active high-affinity T cell clones. Hence, DHODH inhibition may promote recovery of an altered T cell receptor repertoire in autoimmunity.

A Method to Detect Cytochrome c Oxidase Activity and Mitochondrial Proteins in Oligodendrocytes

Cytochrome c oxidase or mitochondrial respiratory chain complex IV is where over 90% of oxygen is consumed. The relationship between complex IV activity and mitochondrial proteins, which provides a guide to understanding the mechanisms in primary mitochondrial disorders, has been determined by histochemistry (complex IV activity) and immunohistochemistry in serial sections. In the central nervous system (CNS), mitochondrial activity and immunoreactivity have been determined in populations of cells in serial sections as capturing cells in more than one section is difficult. In this report, we describe a method to determine complex IV activity in relation to mitochondrial proteins at a single-cell level in the CNS. We performed complex IV histochemistry and immunohistochemistry consecutively in snap-frozen sections. Although the product of complex IV histochemistry reduces the sensitivity of standard immunohistochemistry (secondary antibody and ABC method), the biotin-free Menapath polymer detection system enables mitochondrial proteins to be detected following complex IV histochemistry. The co-occurring chromogens may then be separately visualized and analyzed using multispectral imaging. Our technique is applicable for exploring mitochondrial defects within single cells, including oligodendrocytes, in a variety of CNS disorders and animal models of those diseases.

Loss of protohaem IX farnesyltransferase in mature dentate granule cells impairs short-term facilitation at mossy fibre to CA3 pyramidal cell synapses

KEY POINTS

Neurodegenerative disorders can exhibit dysfunctional mitochondrial respiratory chain complex IV activity. Conditional deletion of cytochrome c oxidase, the terminal enzyme in the respiratory electron transport chain of mitochondria, from hippocampal dentate granule cells in mice does not affect low-frequency dentate to CA3 glutamatergic synaptic transmission. High-frequency dentate to CA3 glutamatergic synaptic transmission and feedforward inhibition are significantly attenuated in cytochrome c oxidase-deficient mice. Intact presynaptic mitochondrial function is critical for the short-term dynamics of mossy fibre to CA3 synaptic function.

ABSTRACT

Neurodegenerative disorders are characterized by peripheral and central symptoms including cognitive impairments which have been associated with reduced mitochondrial function, in particular mitochondrial respiratory chain complex IV or cytochrome c oxidase activity. In the present study we conditionally removed a key component of complex IV, protohaem IX farnesyltransferase encoded by the COX10 gene, in granule cells of the adult dentate gyrus. Utilizing whole-cell patch-clamp recordings from morphologically identified CA3 pyramidal cells from control and complex IV-deficient mice, we found that reduced mitochondrial function did not result in overt deficits in basal glutamatergic synaptic transmission at the mossy-fibre synapse because the amplitude, input-output relationship and 50 ms paired-pulse facilitation were unchanged following COX10 removal from dentate granule cells. However, trains of stimuli given at high frequency (> 20 Hz) resulted in dramatic reductions in short-term facilitation and, at the highest frequencies (> 50 Hz), also reduced paired-pulse facilitation, suggesting a requirement for adequate mitochondrial function to maintain glutamate release during physiologically relevant activity patterns. Interestingly, local inhibition was reduced, suggesting the effect observed was not restricted to synapses with CA3 pyramidal cells via large mossy-fibre boutons, but rather to all synapses formed by dentate granule cells. Therefore, presynaptic mitochondrial function is critical for the short-term dynamics of synapse function, which may contribute to the cognitive deficits observed in pathological mitochondrial dysfunction.

Oxidative Injury and Iron Redistribution Are Pathological Hallmarks of Marmoset Experimental Autoimmune Encephalomyelitis

Oxidative damage and iron redistribution are associated with the pathogenesis and progression of multiple sclerosis (MS), but these aspects are not entirely replicated in rodent experimental autoimmune encephalomyelitis (EAE) models. Here, we report that oxidative burst and injury as well as redistribution of iron are hallmarks of the MS-like pathology in the EAE model in the common marmoset. Active lesions in the marmoset EAE brain display increased expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (p22phox, p47phox, and gp91phox) and inducible nitric oxide synthase immunoreactivity within lesions with active inflammation and demyelination, coinciding with enhanced expression of mitochondrial heat-shock protein 70 and superoxide dismutase 1 and 2. The EAE lesion-associated liberation of iron (due to loss of iron-containing myelin) was associated with altered expression of the iron metabolic markers FtH1, lactoferrin, hephaestin, and ceruloplasmin. The enhanced expression of oxidative damage markers in inflammatory lesions indicates that the enhanced antioxidant enzyme expression could not counteract reactive oxygen and nitrogen species-induced cellular damage, as is also observed in MS brains. This study demonstrates that oxidative injury and aberrant iron distribution are prominent pathological hallmarks of marmoset EAE thus making this model suitable for therapeutic intervention studies aimed at reducing oxidative stress and associated iron dysmetabolism.

The central role of mitochondria in axonal degeneration in multiple sclerosis

Neurodegeneration in multiple sclerosis (MS) is related to inflammation and demyelination. In acute MS lesions and experimental autoimmune encephalomyelitis focal immune attacks damage axons by injuring axonal mitochondria. In progressive MS, however, axonal damage occurs in chronically demyelinated regions, myelinated regions and also at the active edge of slowly expanding chronic lesions. How axonal energy failure occurs in progressive MS is incompletely understood. Recent studies show that oligodendrocytes supply lactate to myelinated axons as a metabolic substrate for mitochondria to generate ATP, a process which will be altered upon demyelination. In addition, a number of studies have identified mitochondrial abnormalities within neuronal cell bodies in progressive MS, leading to a deficiency of mitochondrial respiratory chain complexes or enzymes. Here, we summarise the mitochondrial abnormalities evident within neurons and discuss how these grey matter mitochondrial abnormalities may increase the vulnerability of axons to degeneration in progressive MS. Although neuronal mitochondrial abnormalities will culminate in axonal degeneration, understanding the different contributions of mitochondria to the degeneration of myelinated and demyelinated axons is an important step towards identifying potential therapeutic targets for progressive MS.

Mitochondrial DNA deletions and depletion within paraspinal muscles

Aims

Although mitochondrial abnormalities have been reported within paraspinal muscles in patients with axial weakness and neuromuscular disease as well as with ageing, the basis of respiratory deficiency in paraspinal muscles is not known. This study aimed to determine the extent and basis of respiratory deficiency in paraspinal muscles from cases undergoing surgery for degenerative spinal disease and post mortem cases without a history of spinal disease, where age-related histopathological changes were previously reported.

Methods

Cervical and lumbar paraspinal muscles were obtained peri-operatively from 13 patients and from six post mortem control cases (age range 18–82 years) without a neurological disease. Sequential COX/SDH (mitochondrial respiratory chain complex IV/complex II) histochemistry was performed to identify respiratory-deficient muscle fibres (lacking complex IV with intact complex II activity). Real-time polymerase chain reaction, long-range polymerase chain reaction and sequencing were used to identify and characterize mitochondrial DNA (mtDNA) deletions and determine mtDNA copy number status. Mitochondrial respiratory chain complex subunits were detected by immunohistochemistry.

Results

The density of respiratory-deficient fibres increased with age. On average, 3.96% of fibres in paraspinal muscles were respiratory-deficient (range 0–10.26). Respiratory deficiency in 36.8% of paraspinal muscle fibres was due to clonally expanded mtDNA deletions. MtDNA depletion accounted for further 13.5% of respiratory deficiency. The profile of immunohistochemically detected subunits of complexes was similar in respiratory-deficient fibres with and without mtDNA deletions or mtDNA depletion.

Conclusions

Paraspinal muscles appeared to be particularly susceptible to age-related mitochondrial respiratory chain defects. Clonally expanded mtDNA deletions and focal mtDNA depletion may contribute towards the development of age-related postural abnormalities.

No excess of mitochondrial DNA deletions within muscle in progressive multiple sclerosis

BACKGROUND

Mitochondrial dysfunction is an established feature of multiple sclerosis (MS). We recently described high levels of mitochondrial DNA (mtDNA) deletions within respiratory enzyme-deficient (lacking mitochondrial respiratory chain complex IV with intact complex II) neurons and choroid plexus epithelial cells in progressive MS.

OBJECTIVES

The objective of this paper is to determine whether respiratory enzyme deficiency and mtDNA deletions in MS were in excess of age-related changes within muscle, which, like neurons, are post-mitotic cells that frequently harbour mtDNA deletions with ageing and in disease.

METHODS

In progressive MS cases (n=17), known to harbour an excess of mtDNA deletions in the central nervous system (CNS), and controls (n=15), we studied muscle (paraspinal) and explored mitochondria in single fibres. Histochemistry, immunohistochemistry, laser microdissection, real-time polymerase chain reaction (PCR), long-range PCR and sequencing were used to resolve the single muscle fibres.

RESULTS

The percentage of respiratory enzyme-deficient muscle fibres, mtDNA deletion level and percentage of muscle fibres harbouring high levels of mtDNA deletions were not significantly different in MS compared with controls.

CONCLUSION

Our findings do not provide support to the existence of a diffuse mitochondrial abnormality involving multiple systems in MS. Understanding the cause(s) of the CNS mitochondrial dysfunction in progressive MS remains a research priority.

Clonally expanded mitochondrial DNA deletions within the choroid plexus in multiple sclerosis

Mitochondrial DNA deletions (∆-mtDNA) have been implicated in the pathogenesis of Alzheimer's disease (AD), multiple sclerosis (MS) and Parkinson's disease (PD), as well as ageing. Clonal expansion of ∆-mtDNA is the process by which a mutant mtDNA molecule increases to high levels within a single cell containing both wild-type and mutant mtDNA. Unlike in AD and PD, the diffuse inflammatory process in MS involves the choroid plexus, and mitochondria are exposed to reactive oxygen and nitrogen species over a prolonged period. We determined the extent of respiratory enzyme deficiency and ∆-mtDNA at a single cell level within choroid plexus epithelial cells in MS as well as in AD, PD and controls. The respiratory enzyme-deficient (lacking complex IV and with intact complex II activity) cells were more prevalent within the choroid plexus in AD, MS and PD compared with controls. The main catalytic subunit of complex IV (subunit-I of cytochrome c oxidase) was lacking in significantly more respiratory enzyme-deficient cells in MS compared with AD, PD and controls. The single cell analysis showed a fourfold increase in the percentage of respiratory enzyme-deficient choroid plexus epithelial cells harbouring clonally expanded ∆-mtDNA in MS. Our findings establish clonal expansion of ∆-mtDNA as a feature relatively more prominent within the choroid plexus epithelium in MS than AD, PD or controls. We propose clonal expansion of ∆-mtDNA as a molecular link between inflammation and part of a delayed cellular energy failure in MS.

Loss of myelin-associated glycoprotein in kearns-sayre syndrome

OBJECTIVE

To explore myelin components and mitochondrial changes within the central nervous system in patients with well-characterized mitochondrial disorders due to nuclear DNA or mitochondrial DNA (mtDNA) mutations.

DESIGN

Immunohistochemical analysis, histochemical analysis, mtDNA sequencing, and real-time and long-range polymerase chain reaction were used to determine the pathogenicity of mtDNA deletions.

SETTING

Department of Clinical Pathology, Columbia University Medical Center, and Newcastle Brain Tissue Resource.

PATIENTS

Seventeen patients with mitochondrial disorders and 7 controls were studied from August 1, 2009, to August 1, 2010.

MAIN OUTCOME MEASURE

Regions of myelin-associated glycoprotein (MAG) loss.

RESULTS

Myelin-associated glycoprotein loss in Kearns-Sayre syndrome was associated with oligodendrocyte loss and nuclear translocation of apoptosis-inducing factor, whereas inflammation, neuronal loss, and axonal injury were minimal. In a Kearns-Sayre syndrome MAG loss region, high levels of mtDNA deletions together with cytochrome- c oxidase-deficient cells and loss of mitochondrial respiratory chain subunits (more prominent in the white than gray matter and glia than axons) confirmed the pathogenicity of mtDNA deletions.

CONCLUSION

Primary mitochondrial respiratory chain defects affecting the white matter, and unrelated to inflammation, are associated with MAG loss and central nervous system demyelination.

Relationship between mitochondria and α-synuclein: a study of single substantia nigra neurons

OBJECTIVE

To explore the relationship between α-synuclein pathology and mitochondrial respiratory chain protein levels within single substantia nigra neurons.

DESIGN

We examined α-synuclein and mitochondrial protein expression in substantia nigra neurons of 8 patients with dementia with Lewy bodies, 5 patients with Parkinson disease, and 8 control subjects. Protein expression was determined using immunocytochemistry followed by densometric analysis.

PATIENTS

We examined single substantia nigra neurons from 5 patients with idiopathic Parkinson disease (mean age, 81.2 years), 8 patients with dementia with Lewy bodies (mean age, 75 years), and 8 neurologically and pathologically normal control subjects (mean age, 74.5 years). The control cases showed minimal Lewy body pathology and cell loss. Patients with dementia with Lewy bodies and idiopathic Parkinson disease fulfilled the clinical and neuropathologic criteria for these diseases.

RESULTS

Our results showed that mitochondrial density is the same in nigral neurons with and without α-synuclein pathology. However, there are significantly higher levels of the respiratory chain subunits in neurons containing α-synuclein pathology.

CONCLUSIONS

The finding of increased levels of respiratory chain complex subunits within neurons containing α-synuclein does not support a direct association between mitochondrial respiratory chain dysfunction and the formation of α-synuclein pathology.

Increased mitochondrial content in remyelinated axons: implications for multiple sclerosis

Mitochondrial content within axons increases following demyelination in the central nervous system, presumably as a response to the changes in energy needs of axons imposed by redistribution of sodium channels. Myelin sheaths can be restored in demyelinated axons and remyelination in some multiple sclerosis lesions is extensive, while in others it is incomplete or absent. The effects of remyelination on axonal mitochondrial content in multiple sclerosis, particularly whether remyelination completely reverses the mitochondrial changes that follow demyelination, are currently unknown. In this study, we analysed axonal mitochondria within demyelinated, remyelinated and myelinated axons in post-mortem tissue from patients with multiple sclerosis and controls, as well as in experimental models of demyelination and remyelination, in vivo and in vitro. Immunofluorescent labelling of mitochondria (porin, a voltage-dependent anion channel expressed on all mitochondria) and axons (neurofilament), and ultrastructural imaging showed that in both multiple sclerosis and experimental demyelination, mitochondrial content within remyelinated axons was significantly less than in acutely and chronically demyelinated axons but more numerous than in myelinated axons. The greater mitochondrial content within remyelinated, compared with myelinated, axons was due to an increase in density of porin elements whereas increase in size accounted for the change observed in demyelinated axons. The increase in mitochondrial content in remyelinated axons was associated with an increase in mitochondrial respiratory chain complex IV activity. In vitro studies showed a significant increase in the number of stationary mitochondria in remyelinated compared with myelinated and demyelinated axons. The number of mobile mitochondria in remyelinated axons did not significantly differ from myelinated axons, although significantly greater than in demyelinated axons. Our neuropathological data and findings in experimental demyelination and remyelination in vivo and in vitro are consistent with a partial amelioration of the supposed increase in energy demand of demyelinated axons by remyelination.

Mitochondria as crucial players in demyelinated axons: lessons from neuropathology and experimental demyelination

Mitochondria are the most efficient producers of energy in the form of ATP. Energy demands of axons, placed at relatively great distances from the neuronal cell body, are met by mitochondria, which when functionally compromised, produce reactive oxygen species (ROS) in excess. Axons are made metabolically efficient by myelination, which enables saltatory conduction. The importance of mitochondria for maintaining the structural integrity of myelinated axons is illustrated by neuroaxonal degeneration in primary mitochondrial disorders. When demyelinated, the compartmentalisation of ion channels along axons is disrupted. The redistribution of electrogenic machinery is thought to increase the energy demand of demyelinated axons. We review related studies that focus on mitochondria within unmyelinated, demyelinated and dysmyelinated axons in the central nervous system. Based on neuropathological observations we propose the increase in mitochondrial presence within demyelinated axons as an adaptive process to the increased energy need. An increased presence of mitochondria would also increase the capacity to produce deleterious agents such as ROS when functionally compromised. Given the lack of direct evidence of a beneficial or harmful effect of mitochondrial changes, the precise role of increased mitochondrial presence within axons due to demyelination needs to be further explored in experimental demyelination in-vivo and in-vitro.

Mitochondrial DNA deletions and neurodegeneration in multiple sclerosis

Objective Cerebral atrophy is a correlate of clinical progression in multiple sclerosis (MS). Mitochondria are now established to play a part in the pathogenesis of MS. Uniquely, mitochondria harbor their own mitochondrial DNA (mtDNA), essential for maintaining a healthy central nervous system. We explored mitochondrial respiratory chain activity and mtDNA deletions in single neurons from secondary progressive MS (SPMS) cases.

Methods Ninety-eight snap-frozen brain blocks from 13 SPMS cases together with complex IV/complex II histochemistry, immunohistochemistry, laser dissection microscopy, long-range and real-time PCR and sequencing were used to identify and analyze respiratory-deficient neurons devoid of complex IV and with complex II activity.

Results The density of respiratory-deficient neurons in SPMS was strikingly in excess of aged controls. The majority of respiratory-deficient neurons were located in layer VI and immediate subcortical white matter (WM) irrespective of lesions. Multiple deletions of mtDNA were apparent throughout the gray matter (GM) in MS. The respiratory-deficient neurons harbored high levels of clonally expanded mtDNA deletions at a single-cell level. Furthermore, there were neurons lacking mtDNA-encoded catalytic subunits of complex IV. mtDNA deletions sufficiently explained the biochemical defect in the majority of respiratory-deficient neurons.

Interpretation These findings provide evidence that neurons in MS are respiratory-deficient due to mtDNA deletions, which are extensive in GM and may be induced by inflammation. We propose induced multiple deletions of mtDNA as an important contributor to neurodegeneration in MS.

Development of tissue engineered vascular grafts

Vascular bypass grafting is a commonly performed procedure for ischemic heart disease and peripheral vascular disease. However, approximately one in fourteen patients do not have suitable autologous arteries or veins available for grafting. Synthetic vascular grafts were introduced in the 1960s to overcome these problems, but while they perform adequately in high-flow, large-diameter vessel settings they are generally not suited to low-flow, small-diameter vessels. Tissue engineering is a relatively new discipline that offers the potential to create replacement structures from autologous cells and biodegradable polymer scaffolds. Because tissue engineering constructs contain living cells, they may have the potential to grow, self-repair, and self-remodel. Therefore, recently there has been much interest in the use of this technique to produce low-flow small-diameter arteries. The latest and most exciting developments in this area involve the use of multipotent stem cells as a cell source for tissue engineering of vascular grafts (both in vivo and in vitro).

Bovine spongiform encephalopathy

Early epidemiological studies identified bovine spongiform encephalopathy as a feed-borne infection associated with infected meat-and-bone meal in animal feed. The infection may have derived from scrapie in sheep, a spontaneous genetic mutation in cattle, or a transmissible spongiform encephalopathy in another mammalian species. Experimental work on the risk of transmission has necessarily tried to identify risk materials and their infectivity levels, the nature and size of species barriers, the infectious dose, the route of infection, the strain of the agent and the genotype of the animals at risk. The identification of levels of infection in cattle tissues has aided the removal of risk materials from the human and animal food chains. Maternally associated transmission is unlikely to maintain an outbreak, but the offspring of clinical cases appear to be at greater risk when the rate of food-borne exposure is high. Studies of embryo transfer have not shown infection to be transmitted by this means. While the control measures appeared to be straightforward, compliance has at times proved difficult to enforce and quantify. This has necessitated more extensive prohibitions, aggressive enforcement and thorough auditing of compliance levels.

A role for rho in smooth muscle phenotypic regulation

The role of the small GTP-binding protein Rho in the process of smooth muscle cell (SMC) phenotypic modulation was investigated using cultured rabbit aortic SMCs. Both Rho transcription and Rho protein expression were high for the first 3 days of culture ("contractile" state cells), with expression decreasing after change to the "synthetic" state and peaking upon return to the contractile phenotype. Activation of Rho (indicated by translocation to the membrane) also peaked upon return to the contractile state and was low in synthetic state SMCs. Transient transfection of synthetic state rabbit SMCs with constitutively active Rho (vall4rho) caused a dramatic decrease in cell size and reorganization of cytoskeletal proteins to resemble those of the contractile phenotype; alpha-actin and myosin adopted a tightly packed, highly organized arrangement, whereas vimentin localized to the immediate perinuclear region and focal adhesions were enlarged. Conversely, specific inhibition of endogenous Rho, by expression of C3 transferase, resulted in the complete loss of actin and myosin filaments without affecting the distribution of vimentin. Focal adhesions were reduced in number. Thus, Rho plays a key role in regulating SMC phenotypic expression.

Detection of Escherichia coli O157:H7 in soil and water using multiplex PCR

AIMS

To evaluate the suitability of a multiplex PCR-based assay for sensitive and rapid detection of Escherichia coli O157:H7 in soil and water.

METHODS AND RESULTS

Soil and water samples were spiked with E. coli O157:H7 and subjected to two stages of enrichment prior to multiplex PCR. Detection sensitivities were as high as 1 cfu ml(-1) drinking water and 2 cfu g(-1) soil. Starvation of E. coli O157:H7 for 35 d prior to addition to soil did not affect the ability of the assay to detect initial cell numbers as low as 10 cfu g(-1) soil. Use of an 8-h primary enrichment enabled detection of as few as 6 cfu g(-1) soil, and 10(4) cfu g(-1) soil with a 6-h primary enrichment. When soil was inoculated with 10(5) cfu g(-1), the PCR assay indicated persistence of E. coli O157:H7 during a 35 d incubation. However, when soil was inoculated with lower numbers of pathogen, PCR amplification signals indicated survival to be dependent on cell concentration.

CONCLUSIONS

A multiplex PCR-based assay, in combination with an enrichment strategy enabled sensitive and rapid detection of E. coli O157:H7 in soil and water.

SIGNIFICANCE AND IMPACT OF THE STUDY

The ability to sensitively detect E.coli O157:H7 in environmental material within one working day represents a considerable advancement over alternative more time-consuming methods for detection of this pathogen.

Neointimal formation by circulating bone marrow cells

The origin of smooth muscle cells involved in vascular healing was examined. Eighteen C57BL/6 (Ly 5.2) female mice underwent whole body irradiation followed by transfusion with 106 bone nucleated marrow cells from congenic (Ly 5.1) male donors. Successful repopulation by donor marrow was demonstrated after 4 weeks by flow cytometry with FITC-conjugated A20.1/Ly 5.1 monoclonal antibody. The iliac artery of six of the chimeric mice was scratch-injured by five passes of a probe, causing severe medial damage. After 4 weeks the arterial lumen was obliterated by a cell-rich neointima, with alpha-smooth muscle actin-containing cells present around the residual lumen. Approximately half of these cells were of male donor origin, as evidenced by in situ hybridization with a Y chromosome-specific probe. An organized arterial thrombus was formed in the remaining 12 chimeric mice by inserting an 8-0 silk suture into the left common carotid artery. Donor cells staining with alpha-smooth muscle actin were found in those arteries sustaining serious damage but not in arteries with minimal damage. Our results suggest that bone marrow-derived cells are recruited in vascular healing as a complementary source of smooth muscle-like cells when the media is severely damaged and few resident smooth muscle cells are available to effect repair.

Reorganization of structural proteins in vascular smooth muscle cells grown in collagen gel and basement membrane matrices (Matrigel): a comparison with their in situ counterparts

When smooth muscle cells are enzyme-dispersed from tissues they lose their original filament architecture and extracellular matrix surrounds. They then reorganize their structural proteins to accommodate a 2-D growth environment when seeded onto culture dishes. The aim of the present study was to determine the expression and reorganization of the structural proteins in rabbit aortic smooth muscle cells seeded into 3-D collagen gel and Matrigel (a basement membrane matrix). It was shown that smooth muscle cells seeded in both gels gradually reorganize their structural proteins into an architecture similar to that of their in vivo counterparts. At the same time, a gradual decrease in levels of smooth muscle-specific contractile proteins (mainly smooth muscle myosin heavy chain-2) and an increase in beta-nonmuscle actin occur, independent of both cell growth and extracellular matrix components. Thus, smooth muscle cells in 3-D extracellular matrix culture and in vivo have a similar filament architecture in which the contractile proteins such as actin, myosin, and alpha-actinin are organized into longitudinally arranged "myofibrils" and the vimentin-containing intermediate filaments form a meshed cytoskeletal network. However, the myofibrils reorganized in vitro contain less smooth muscle-specific and more nonmuscle contractile proteins.

Vascular smooth muscle cell phenotypic modulation in culture is associated with reorganisation of contractile and cytoskeletal proteins

Smooth muscle cells (SMC) exhibit a functional plasticity, modulating from the mature phenotype in which the primary function is contraction, to a less differentiated state with increased capacities for motility, protein synthesis, and proliferation. The present study determined, using Western analysis, double-label immunofluorescence and confocal microscopy, whether changes in phenotypic expression of rabbit aortic SMC in culture could be correlated with alterations in expression and distribution of structural proteins. "Contractile" state SMC (days 1 and 3 of primary culture) showed distinct sorting of proteins into subcellular domains, consistent with the theory that the SMC structural machinery is compartmentalised within the cell. Proteins specialised for contraction (alpha-SM actin, SM-MHC, and calponin) were highly expressed in these cells and concentrated in the upper central region of the cell. Vimentin was confined to the body of the cell, providing support for the contractile apparatus but not co-localising with it. In line with its role in cell attachment and motility, beta-NM actin was localised to the cell periphery and basal cortex. The dense body protein alpha-actinin was concentrated at the cell periphery, possibly stabilising both contractile and motile apparatus. Vinculin-containing focal adhesions were well developed, indicating the cells' strong adhesion to substrate. In "synthetic" state SMC (passages 2-3 of culture), there was decreased expression of contractile and adhesion (vinculin) proteins with a concomitant increase in cytoskeletal proteins (beta-non-muscle [NM] actin and vimentin). These quantitative changes in structural proteins were associated with dramatic changes in their distribution. The distinct compartmentalisation of structural proteins observed in "contractile" state SMC was no longer obvious, with proteins more evenly distributed throughout the cytoplasm to accommodate altered cell function. Thus, SMC phenotypic modulation involves not only quantitative changes in contractile and cytoskeletal proteins, but also reorganisation of these proteins. Since the cytoskeleton acts as a spatial regulator of intracellular signalling, reorganisation of the cytoskeleton may lead to realignment of signalling molecules, which, in turn, may mediate the changes in function associated with SMC phenotypic modulation.

Molecular basis by which garlic suppresses atherosclerosis

The aim of this study was to determine the mechanism by which the aged garlic extract "Kyolic" has a protective effect against atherosclerosis. Plasma cholesterol of rabbits fed a 1% cholesterol-enriched diet for 6 wk was not reduced by supplementation with 800 microL Kyolic/(kg body. d). In spite of this, Kyolic reduced by 64% (P < 0.05) the surface area of the thoracic aorta covered by fatty streaks and significantly reduced aortic arch cholesterol. Kyolic also significantly inhibited by approximately 50% the development of thickened, lipid-filled lesions in preformed neointimas produced by Fogarty 2F balloon catheter injury of the right carotid artery in cholesterol-fed rabbits. In vitro studies found that Kyolic completely prevented vascular smooth muscle phenotypic change from the contractile, high volume fraction of filament (V(v)myo) state, and inhibited proliferation of smooth muscle cells in the synthetic state with a 50% effective dose (ED(50)) of 0.2%. Kyolic also slightly inhibited the accumulation of lipid in cultured macrophages but not smooth muscle, and had no effect on the expression of adhesion molecules on the surface of the endothelium or the adherence of leukocytes. It is concluded that Kyolic exerts antiatherogenic effects through inhibition of smooth muscle phenotypic change and proliferation, and by another (unclarified) effect on lipid accumulation in the artery wall.

Circulating bone marrow cells can contribute to neointimal formation

To examine the source of smooth muscle-like cells during vascular healing, C57BL/6 (Ly 5.2) female mice underwent whole body irradiation followed by transfusion with 10(6) nucleated bone marrow cells from congenic (Ly 5.1) male donors. Successful repopulation (88.4 +/- 4.9%) by donor marrow was demonstrated in the female mice by flow cytometry with FITC-conjugated A20.1/Ly 5.1 monoclonal antibody after 4 weeks. The arteries of the female mice were then subjected to two types of insult: (1) The iliac artery was scratch-injured by 5 passes of a probe causing severe medial damage. After 4 weeks, the arterial lumen was obliterated by a cell-rich neointima, with cells containing alpha smooth muscle actin present around the residual lumen. Approximately half of these cells were of male donor origin, as evidenced by in situ hybridization with a Y-chromosome-specific probe. (2) In an organized arterial thrombus formed by inserting an 8-0 silk suture into the left common carotid artery, donor cells staining with alpha smooth muscle actin were found in those arteries sustaining serious damage but not in arteries with minimal damage. Our results suggest that bone marrow-derived cells are recruited in vascular healing as a complementary source of smooth muscle-like cells when the media is severely damaged and few resident smooth muscle cells are available to effect repair.

Relationship of glycosaminoglycan and matrix changes to vascular smooth muscle cell phenotype modulation in rabbit arteries after acute injury

PURPOSE

The phenotype of vascular smooth muscle cells (SMCs) is altered in several arterial pathologies, including the neointima formed after acute arterial injury. This study examined the time course of this phenotypic change in relation to changes in the amount and distribution of matrix glycosaminoglycans.

METHODS

The immunochemical staining of heparan sulphates (HS) and chondroitin sulphates (CS) in the extracellular matrix of the arterial wall was examined at early points after balloon catheter injury of the rabbit carotid artery. SMC phenotype was assessed by means of ultrastructural morphometry of the cytoplasmic volume fraction of myofilaments. The proportions of cell and matrix components in the media were analyzed with similar morphometric techniques.

RESULTS

HS and CS were shown in close association with SMCs of the uninjured arterial media as well as being more widespread within the matrix. Within 6 hours after arterial injury, there was loss of the regular pericellular distribution of both HS and CS, which was associated with a significant expansion in the extracellular space. This preceded the change in ultrastructural phenotype of the SMCs. The glycosaminoglycan loss was most exaggerated at 4 days, after which time the HS and CS reappeared around the medial SMCs. SMCs of the recovering media were able to rapidly replace their glycosaminoglycans, whereas SMCs of the developing neointima failed to produce HS as readily as they produced CS.

CONCLUSIONS

These studies indicate that changes in glycosaminoglycans of the extracellular matrix precede changes in SMC phenotype after acute arterial injury. In the recovering arterial media, SMCs replace their matrix glycosaminoglycans rapidly, whereas the newly established neointima fails to produce similar amounts of heparan sulphates.

Heterogeneous distribution of isoactins in cultured vascular smooth muscle cells does not reflect segregation of contractile and cytoskeletal domains

We have previously demonstrated that alpha-smooth muscle (alpha-SM) actin is predominantly distributed in the central region and beta-non-muscle (beta-NM) actin in the periphery of cultured rabbit aortic smooth muscle cells (SMCs). To determine whether this reflects a special form of segregation of contractile and cytoskeletal components in SMCs, this study systematically investigated the distribution relationship of structural proteins using high-resolution confocal laser scanning fluorescent microscopy. Not only isoactins but also smooth muscle myosin heavy chain, alpha-actinin, vinculin, and vimentin were heterogeneously distributed in the cultured SMCs. The predominant distribution of beta-NM actin in the cell periphery was associated with densely distributed vinculin plaques and disrupted or striated myosin and alpha-actinin aggregates, which may reflect a process of stress fiber assembly during cell spreading and focal adhesion formation. The high-level labeling of alpha-SM actin in the central portion of stress fibers was related to continuous myosin and punctate alpha-actinin distribution, which may represent the maturation of the fibrillar structures. The findings also suggest that the stress fibers, in which actin and myosin filaments organize into sarcomere-like units with alpha-actinin-rich dense bodies analogous to Z-lines, are the contractile structures of cultured SMCs that link to the network of vimentin-containing intermediate filaments through the dense bodies and dense plaques.

Effects of collagen gel configuration on behavior of vascular smooth muscle cells in vitro: association with vascular morphogenesis

The growth, behavior, and contractile protein expression of rabbit aortic smooth muscle cells (SMC) grown on, between layers, or within a collagen gel was investigated by confocal laser scanning fluorescence microscopy and Western analysis. SMC grown on collagen gel behaved similarly to those on conventional culture dishes. However, when a second layer of collagen was overlaid, cells underwent an elongated quiescent phase before onset of proliferation and a more than threefold lower logarithmic growth rate was observed. These cells self-organized into a network with ring-like structures. With increasing culture time, some of the rings developed into funnel-like, incomplete or complete tubular structures. If a tubular template preexisted within the gel, the SMC established a cylinder-shaped tube with several circularly arranged muscular layers (similar to an artery wall). This behavior mimicked endothelial cells during angiogenesis in vitro. A similar phenomenon occurred in cultures in which SMC were randomly mixed in a collagen gel, but here their behavior and morphology varied with their position within the gel. Western blot analysis showed that the SMC differentiation marker, smooth muscle myosin heavy chain-2 (SM-2), rapidly decreased, disappearing by day 10 in SMC grown on collagen, but was still detectable until day 25 in cells cultured between or within the same gel. These findings indicate that like endothelial cells, vascular SMC can display blood vessel formation behavior in vitro when an appropriate three-dimensional matrix environment is provided to keep them in a relatively higher-differentiated and low-proliferative state.

The effect of environmental cues on the differentiation of myofibroblasts in peritoneal granulation tissue

This study investigated the effect of haemodynamic stress, active stretch, and neuronal input on the differentiation of myofibroblasts in peritoneal granulation tissue. Lengths of silastic tubing (10 mm long x 3 mm diameter) were placed in the peritoneal cavity of the rat. By 2 weeks, a capsule of granulation tissue had formed around the tubing. This capsule consisted of several layers of myofibroblasts and the matrix that they had produced, overlaid by a single layer of mesothelial cells. The silastic tubing was removed and at the same time, the living tube of tissue was everted so that the mesothelium now lined its inner surface. To examine the effect of haemodynamic factors on myofibroblast differentiation, the 10 mm long tubes of mesothelial-lined granulation tissue were transplanted into the severed abdominal aorta of the same rat in which the granulation tissue was grown. End-to-end anastomoses were performed to extend the existing aorta. At 1, 2, and 3 months post-transplantation, the grafts were removed and a progressive increase in the percent volume fraction of myofilaments (% V(v)myo) was observed (from 35.7+/-1.6% to 58.7 3+/-1.4%; p<0.05). To determine whether the active stretching that occurs in vivo could account for differentiation of the constituent myofibroblasts, tubes of granulation tissue were placed into a mechanical device in which they underwent continuous stretching of 5-10% elongation from the resting position at 50 cycles per minute for 3, 24 or 72 h. This caused a significant (p<0. 05) increase in %V(v)myo after 72 h. Granulation tissue was also transplanted into the rat anterior eye chamber, where it became surrounded by adrenergic nerves supplying the host iris. Two months after implantation, there was no significant change in the %V(v)myo of the myofibroblasts (35.7+/-1.6% to 33.3+/-2.7%). These studies show that myofibroblasts of the granulation tissue encapsulating free-floating foreign bodies in the peritoneal cavity further differentiate towards a smooth muscle phenotype when transplanted into a smooth muscle environment, namely the abdominal aorta. Similar changes are seen when the granulation tissue is subjected to active, intermittent stretch in vitro, while the presence of nerves has no effect.

Haemopoietic origin of myofibroblasts formed in the peritoneal cavity in response to a foreign body

This study utilized both in vivo and in vitro techniques to investigate whether cells of bone marrow origin can differentiate into smooth muscle-like cells (myofibroblasts) with contractile filaments and proteins. Female C57BL/6 mice expressing the Ly5.2 antigen on the surface of their haemopoietic cells had four pieces of silastic tubing (3 x 0.5 mm outer diameter) or boiled blood clot (2-3 mm diameter) placed in their peritoneal cavity. After 3, 5, 7 and 14 days (n = 4/group) the implants were removed and those that had remained free-floating were processed for light microscopy, immunohistochemistry and electron microscopy. In the first 3-5 days, rounded cells adhered to the entire surface of the tubing then flattened. These cells stained with fluoresceinated antibodies to Ly5.2 showing that they were derived from haemopoietic cells. By 14 days the cells had become elongated and multilayered in a collagen matrix, forming a thick tissue capsule around the tubing or boiled clot. They contained contractile filaments and stained with antibodies to alpha-smooth muscle actin but no longer stained for Ly5.2. A separate set of female C57BL/6 Ly5.2 mice were X-irradiated to destroy bone marrow then immediately transfused with 10(6) nucleated bone marrow cells taken from the femur and tibia of a congenic strain of male mice expressing the Ly5.1 allele. Eight of the female mice with successful engraftment (80-99%) had silastic tubing implanted in the peritoneal cavity. After 14 days, in situ hybridization with Y chromosome probe confirmed the male donor, and thus bone marrow, origin of the elongated cells that formed the capsule. In vitro studies showed that cells of the murine macrophage cell lines RAW 264.7 and J774 express alpha-smooth muscle actin after exposure to the cytokine gamma-interferon in vitro. These data show that bone marrow-derived cells can differentiate into smooth muscle-like cells and raises the possibility that blood-derived cells may contribute to the development of fibro-proliferative vascular diseases such as atherosclerosis.

Oral administration of inducible nitric oxide synthase inhibitors reduces nitric oxide synthesis but has no effect on the severity of experimental colitis

BACKGROUND

Increased concentrations of nitrate and nitrite (the breakdown products of nitric oxide) in the serum and faeces of patients with inflammatory bowel disease (IBD) suggests that increased synthesis of nitric oxide occurs in IBD. The aim of this study was to assess aminoguanidine (AMG), a selective inhibitor of inducible nitric oxide synthase, with regard to its effectiveness as a nitric oxide inhibitor and as a modulator of inflammation in trinitrobenzene sulfonic acid (TNBS)-induced colitis.

MATERIALS AND METHODS

Colitis was induced in Wistar rats. Selective (AMG) and non-selective (1-nitroso-arginine methyl ester (1-NAME)) inhibitors of nitric oxide synthase were given in the drinking water. Colonic citrulline and arginine concentrations were assessed using high-performance liquid chromatography. The severity of colitis was assessed by a macroscopic scoring system.

RESULTS

Both 1-NAME and AMG successfully reduced nitric oxide synthesis. There was no evidence of substrate depletion in the colonic wall. Neither of the agents reduced the severity of colonic inflammation.

CONCLUSIONS

Oral administration of nitric oxide synthase inhibitors reduced nitric oxide synthesis in the colonic wall. This study does not provide evidence to support a role for nitric oxide in the pathogenesis of colonic inflammation in TNBS colitis.

Vascular smooth muscle and arterial calcification

Smooth muscle cultures can calcify under certain circumstances. As a model system these cultures therefore provide information on why calcification occurs in atherosclerotic plaques. Whether all smooth muscle cells (under certain conditions), or only specific populations, can produce this mineralization has not been resolved. Demer's group has cloned calcifying vascular cells from subcultured bovine aorta and studied them in detail. They have speculated on whether the cells are smooth muscle which have altered in phenotype, or whether they are derived from a stem cell population within the artery wall. The article argues that while the normal process of smooth muscle phenotypic modulation seen in arterial repair could account for the observations, this view may be two simplistic considering the complex nature of the artery wall. Certainly there is evidence for heterogeneity of smooth muscle cells in the artery wall and recent evidence suggests that stem cells can circulate in the blood and repopulate tissues. Further studies are required to resolve the important question as to the origin of cells which produce mineralization in atheroma.

Blood vessels from bone marrow

Lengths of silastic tubing were inserted into the peritoneal cavity of rats or rabbits. By two weeks the free-floating implants had become covered by a capsule consisting of several layers of "macrophage"-derived myofibroblasts and collagen matrix overlaid by a single layer of mesothelial cells. The tubing was removed from the harvested implant and the tissue everted. This now resembled an artery with an inner lining of mesothelial cells (the "intima"), a "media" of myofibroblasts, and an outer collagenous "adventitia." The tube of living tissue was grafted by end-to-end anastomoses into the transected carotid artery or abdominal aorta of the same animal in which the tissue had been grown, where it remained patent for four months and developed structures resembling elastic lamellae. The myofibroblasts developed a high volume fraction of myofilaments and became responsive to contractile and relaxing agents similar to smooth muscle cells of the adjacent artery wall.

ICAM-1 expression by vascular smooth muscle cells is phenotype-dependent

Atherosclerosis is an inflammatory disease characterised by increased expression of adhesion molecules for leukocytes on both the surface of dysfunctional endothelium and on smooth muscle cells (SMC) within the lesion. It is also characterised by altered SMC phenotypic expression, indicated by a decreased volume fraction of myofilaments (V(v)myo) [1,2] and changes in gene expression [3]. The present study used an in vitro model to investigate, by immunofluorescence staining and flow cytometry, the influence of phenotype on vascular SMC expression of the adhesion molecule for leukocytes, intracellular adhesion molecule-1 (ICAM-1), and the regulatory mechanisms involved in this process. Smooth muscle cells with a high V(v)myo, freshly isolated from rat aortic media, expressed little or no ICAM-1 and this could not be induced by interleukin-1beta (IL-1beta). As SMC modulated phenotype, indicated by decreasing V(v)myo over the first 5 days of culture, there was a concomitant increase in ICAM-1 expression. At day 9 of primary culture, when SMC cultures had returned to the high V(v)myo phenotype, ICAM-1 expression was markedly lower. However, these cells retained the capacity to express ICAM-1 in response to IL-1beta. After several passages in culture, cells (with a low V(v)myo) constitutively expressed ICAM-1, with levels further up-regulated in response to IL-1beta. These changes in ICAM-1 expression were not related to proliferative state, since similar results were obtained with growth arrested SMC. Investigation of signalling pathways involved in regulating ICAM-1 expression by primary vascular SMC suggested a complex regulatory mechanism. Activation of adenyl cyclase (with forskolin) caused a significant increase in cells expressing ICAM-1. Treatment with inhibitors of protein kinase C (chelerythrine chloride), protein tyrosine kinase (genistein), or the transcription factor NF-kappaB (PDTC) had no significant effect on IL-1-induced ICAM-1 expression. However, in the presence of serum, both genistein and PDTC caused a significant increase in basal expression. The results indicate that ICAM-1 expression by SMC is phenotype-dependent, with expression evident only after cells have modulated to a low V(v)myo phenotype. They also indicate the existence of complex regulatory mechanisms, possibly involving the SMC cytoskeleton.

Novel vascular graft grown within recipient's own peritoneal cavity

A method by which to overcome the clinical symptoms of atherosclerosis is the insertion of a graft to bypass an artery blocked or impeded by plaque. However, there may be insufficient autologous mammary artery for multiple or repeat bypass, saphenous vein may have varicose degenerative alterations that can lead to aneurysm in high-pressure sites, and small-caliber synthetic grafts are prone to thrombus induction and occlusion. Therefore, the aim of the present study was to develop an artificial blood conduit of any required length and diameter from the cells of the host for autologous transplantation. Silastic tubing, of variable length and diameter, was inserted into the peritoneal cavity of rats or rabbits. By 2 weeks, it had become covered by several layers of myofibroblasts, collagen matrix, and a single layer of mesothelium. The Silastic tubing was removed from the harvested implants, and the tube of living tissue was everted such that it now resembled a blood vessel with an inner lining of nonthrombotic mesothelial cells (the "intima"), with a "media" of smooth muscle-like cells (myofibroblasts), collagen, and elastin, and with an outer collagenous "adventitia." The tube of tissue (10 to 20 mm long) was successfully grafted by end-to-end anastomoses into the severed carotid artery or abdominal aorta of the same animal in which they were grown. The transplant remained patent for at least 4 months and developed structures resembling elastic lamellae. The myofibroblasts gained a higher volume fraction of myofilaments and became responsive to contractile agonists, similar to the vessel into which they had been grafted. It is suggested that these nonthrombogenic tubes of living tissue, grown in the peritoneal cavity of the host, may be developed as autologous coronary artery bypass grafts or as arteriovenous access fistulae for hemodialysis patients.

Matrix metalloproteinase can facilitate the heparanase-induced promotion of phenotype change in vascular smooth muscle cells

Previous studies from this laboratory have shown that degradation of heparan sulphate proteoglycan by both living macrophages and macrophage lysosomal heparanase induces phenotypic change of vascular smooth muscle cells (SMC) from a high volume fraction of myofilaments (V(v)myo) to a low V(v)myo [Campbell et al. Exp Cell Res 1992; 200: 156-167]. The aim of this study was to determine whether matrix metalloproteinase (MMP) activity is also involved in the induction of SMC phenotypic change by macrophages. A specific inhibitor of MMPs (BB94) was able to block macrophage-induced SMC phenotypic change and subsequent DNA synthesis in freshly dispersed SMC seeded in primary culture at confluent density. The inhibitor did not block these SMC changes when SMC were seeded at low density without macrophages nor did it block heparanase activity directly. We also determined whether heparanase and MMP activities are upregulated together in vivo. Artery homogenates were analysed in a heparanase enzyme assay and for MMPs using zymograms. Increased heparanase activity was observed 3-14 days following balloon catheter injury of rabbit carotid arteries, and returned to control levels 6 weeks after injury. Active MMP2 was induced with heparanase after injury. MMP9 induction was also apparent 6 h after injury. Immunohistology on sections of these arteries showed the presence of MMPI1, 2, 3 and 9 with these MMPs being strongly induced in the intima 7 days after balloon catheter injury. Both heparanase and MMP activities were also present in human end-stage complex lesions from coronary arteries, carotid endarterectomies and abdominal aortic aneurysms. Because MMPs and heparanase are expressed at the same time, it is possible that MMPs facilitate heparanase activity in promotion of phenotypic modulation of SMC in vivo during neointimal thickening following injury and in atherosclerotic lesions.

Characterization of the Kupffer cell response to exogenous endotoxin in a rodent model of obstructive jaundice

BACKGROUND

Sepsis and endotoxaemia occur frequently in biliary obstruction. Impaired Kupffer cell endocytosis is implicated in these events. Tumour necrosis factor and interleukin 6, secreted by Kupffer cells, are important mediators of sepsis. Kupffer cell clearance of endotoxin and secretion of cytokines in experimental obstructive jaundice were investigated.

METHODS

Wistar rats were randomized to bile duct ligation, sham operation or control. Groups (n = 8) were studied 1 and 3 weeks after operation. Kupffer cell function was assessed using in situ hepatic perfusion.

RESULTS

Clearance of endotoxin was significantly depressed 1 week (median (interquartile range) 20.3 (10.5-27.1) per cent) and 3 weeks (22.1 (20.2-23.2) per cent) after bile duct ligation compared with that in respective sham animals (35.5 (29.9-41.6) and 40.9 (37.7-47.0) per cent) and controls (39.5 (37.3-46.8) per cent). Secretion of tumour necrosis factor was significantly greater 1 week (1113.7 (706.5-1436. 8) pg/ml) and 3 weeks (1118.2 (775.7-1484.1) pg/ml) following bile duct ligation compared with that in respective sham animals (114.3 (0-178.5) and 107.6 (63.7-166.4) pg/ml) and controls (0 (0-20.7) pg/ml). Interleukin 6 was not secreted by sham or control animals but was present in the perfusate from jaundiced animals at 1 and 3 weeks (52.5 (9.9-89.5) and 66.2 (60.2-193.1) pg/ml).

CONCLUSION

These data demonstrate simultaneous impairment of Kupffer cell clearance of endotoxin and increased secretion of proinflammatory cytokines in experimental obstructive jaundice. These diverse responses may contribute to the development of sepsis-related complications in biliary obstruction.

Different phenotypic classes of Sinorhizobium meliloti mutants defective in synthesis of K antigen

For Sinorhizobium meliloti (also known as Rhizobium meliloti) AK631 to establish effective symbiosis with alfalfa, it must be able to synthesize a symbiotically active form of its K antigen, a capsular polysaccharide containing a Kdo (3-deoxy-D-manno-octulosonic acid) derivative. Previously isolated mutants defective in the synthesis of K antigen are resistant to bacteriophage phi16-3. By screening ca. 100,000 Tn5-mutagenized R. meliloti bacteria for resistance to bacteriophage phi16-3, we isolated 119 mutants, 31 of which could not be complemented by genes previously identified as being required for K-antigen synthesis. Of these 31 new mutants, 13 were symbiotically defective and lacked the K antigen. Through genetic and phenotypic analyses, we have grouped these mutants into four distinct classes. Although all of these mutants lack the K antigen, many also have altered lipopolysaccharides (LPS), suggesting that the biochemical pathways for the synthesis of K antigen and LPS have common enzymatic steps. In addition, we have found that these and other classes of K-antigen-defective mutants of S. meliloti AK631 exhibit unique patterns of sensitivities to phage strains to which the parental strain was resistant. Our studies have identified new classes of genes required for both the synthesis of K antigen and the symbiotic proficiency of S. meliloti AK631. Some of these classes of genes also play a role in LPS synthesis.

Effect of estrogen on vascular smooth muscle cells is dependent upon cellular phenotype

To investigate the growth-regulating action of estrogen on vascular smooth muscle cells (SMC), effects of beta-17-estradiol (beta-E2) on phenotypic modulation and proliferation of rabbit aortic SMC were observed in vitro. At 10(-8)M, beta-E2 significantly slowed the decrease in volume fraction of myofilaments (Vv myo) of freshly dispersed SMCs in primary culture, indicating an inhibitory effect of beta-E2 on spontaneous phenotypic modulation of SMC from a contractile to a synthetic phenotype. Freshly dispersed SMCs treated with beta-E2 also had a relatively longer quiescent phase than control cells before intense proliferation occurred. This was in contrast to SMCs in passage 2 3 (synthetic state), where beta-E2-treated cells replicated significantly faster than untreated cells. beta-E2 also markedly enhanced the serum-induced DNA synthesis of synthetic SMCs in a concentration-dependent manner within physiological range (10(-10)to 10(-8)M). These findings indicate that the growth-regulating effect of estrogen on vascular SMC is dependent on the cell's phenotypic state. It delays the cell cycle re-entry of the contractile SMCs by retarding their phenotypic modulation: however, once cells have modulated to the synthetic phenotype, it promotes their replication.

Arterial heparan sulfate proteoglycans inhibit vascular smooth muscle cell proliferation and phenotype change in vitro and neointimal formation in vivo

PURPOSE

The aim of this study was to determine whether heparan sulfate proteoglycans (HSPGs) from the normal arterial wall inhibit neointimal formation after injury in vivo and smooth muscle cell (SMC) phenotype change and proliferation in vitro.

METHODS

Arterial HSPGs were extracted from rabbit aortae and separated by anion-exchange chromatography. The effect of HSPGs, applied in a periadventitial gel, on neointimal formation was assessed 14 days after balloon catheter injury of rabbit carotid arteries. Their effect on SMC phenotype and proliferation was measured by point-counting morphometry of the cytoplasmic volume fraction of myofilaments (Vvmyo) and 3H-thymidine incorporation in SMCs in culture.

RESULTS

Arterial HSPGs (680 microg) reduced neointimal formation by 35% at 14 days after injury (P=.029), whereas 2000 microg of the low-molecular-weight heparin Enoxaparin was ineffective. HSPGs at 34 microg/mL maintained subconfluent primary cultured SMCs with the same high Vvmyo (52.1%+/-13.8%) after 5 days in culture as did cells freshly isolated from the arterial wall (52.1%+/-15.1%). In contrast, 100 microg/mL Enoxaparin was ineffective in preventing phenotypic change over this time period (Vvmyo 38.9%+/-14.6%, controls 35.9%+/-12.8%). HSPGs also inhibited 3H-thymidine incorporation into primary cultured SMCs with an ID50 value of 0.4 microg/mL compared with a value of 14 microg/mL for Enoxaparin (P< .01).

CONCLUSION

When used periadventitially in the rabbit arterial injury model, natural arterial HSPGs are effective inhibitors of neointimal formation. In vitro, the HSPGs maintain SMCs in a quiescent state by inhibiting phenotypic change and DNA synthesis. This study suggests that HSPGs may be a natural agent for the treatment of clinical restenosis.

Changes in three-dimensional architecture of microfilaments in cultured vascular smooth muscle cells during phenotypic modulation

To investigate changes in the three-dimensional microfilament architecture of vascular smooth muscle cells (SMC) during the process of phenotypic modulation, rabbit aortic SMCs cultured under different conditions and at different time points were either labelled with fluorescein-conjugated probes to cytoskeletal and contractile proteins for observation by confocal laser scanning microscopy, or extracted with Triton X-100 for scanning electron microscopy. Densely seeded SMCs in primary culture, which maintain a contractile phenotype, display prominent linear myofilament bundles (stress fibres) that are present throughout the cytoplasm with alpha-actin filaments predominant in the central part and beta-actin filaments in the periphery of the cell. Intermediate filaments form a meshed network interconnecting the stress fibres and linking directly to the nucleus. Moderately and sparsely seeded SMCs, which modulate toward the synthetic phenotype during the first 5 days of culture, undergo a gradual redistribution of intermediate filaments from the perinuclear region toward the peripheral cytoplasm and a partial disassembly of stress fibres in the central part of the upper cortex of the cytoplasm, with an obvious decrease in alpha-actin and myosin staining. These changes are reversed in moderately seeded SMCs by day 8 of culture when they have reached confluence. The results reveal two changes in microfilament architecture in SMCs as they undergo a change in phenotype: the redistribution of intermediate filaments probably due to an increase in synthetic organelles in the perinuclear area, and the partial disassembly of stress fibres which may reflect a degradation of contractile components.

Clinical and biochemical determinants of plasma lipid peroxide levels in type 2 diabetes

The enhanced risk and increased severity of atheroma in diabetes is well recognized but, as yet, incompletely explained. A cross-sectional study of vascular disease risk factors in a group of type 2 diabetic patients from South West Scotland has revealed an association between glycaemic control, assessed by HbAl level and plasma lipid peroxides measured by a specific high-performance liquid chromatography method. Duration of diabetes appeared to be a subsidiary contributor to lipid peroxidation. We suggest this evidence supports the importance of glycaemic control in modulating glyco-oxidative mechanisms probably crucial to production of diabetic complications. Atherosclerosis prevention in diabetes may hinge on exemplary simultaneous control of both hyperglycaemia and hyperlipidaemia.

Induction of smooth muscle cell nitric oxide synthase by human leukaemia inhibitory factor: effects in vitro and in vivo

We have previously shown that human leukaemia inhibitory factor (hLIF) inhibits perivascular cuff-induced neointimal formation in the rabbit carotid artery. Since nitric oxide (NO) is a known inhibitor of smooth muscle growth, NO synthase (NOS) activity in the presence of hLIF was examined in vivo and in vitro. In rabbit aortic smooth muscle cell (SMC) culture, significant NOS activity was observed at 50 pg/ml hLIF, with maximal activity at 5 ng/ml. In the presence of the NOS inhibitor L-NAME, hLIF-induced activation of NOS was greatly decreased, however it was still 63-fold higher than in control (p < 0.05). SMC-DNA synthesis was significantly reduced (-47%) following incubation with hLIF plus L-arginine, the substrate required for NO production (p < 0.05), with no effect observed in the absence of L-arginine. Silastic cuff placement over the right carotid artery of rabbits resulted in a neointima 19.3 +/- 5.4% of total wall cross-sectional area, which was increased in the presence of L-NAME (27.0 +/- 2.0%; p < 0.05) and reduced in the presence of L-arginine (11.3 +/- 2.0%; p < 0.05). The effect of L-arginine was ameliorated by co-administration of L-NAME (16.4 +/- 1.5%). However, administration of L-NAME with hLIF had no effect on the potent inhibition of neointimal formation by hLIF (3.2 +/- 2.5 vs. 2.1 +/- 5.4%, respectively). Similarly, with hLIF administration, NOS activity in the cuffed carotid increased to 269.0 +/- 14.0% of saline-treated controls and remained significantly higher with co-administration of L-NAME (188.5 +/- 14.7%). These results indicate that hLIF causes superinduction of NO by SMC, and that it is, either partially or wholly, through this mechanism that hLIF is a potent inhibitor of neointimal formation in vivo and of smooth muscle proliferation in vitro.

The cell biology of atherosclerosis--new developments

In the development of atherosclerotic lesions, three basic processes occur: 1) invasion of the artery wall by leucocytes, particularly monocytes and T-lymphocytes; 2) smooth muscle phenotypic modulation, proliferation, and synthesis of extracellular matrix; and 3) intracellular (macrophage and smooth muscle) lipoprotein uptake and lipid accumulation. Invasion of the vessel wall by leucocytes is mediated through the expression of adhesion molecules on both leucocytes and the endothelium making them 'sticky'. The adhesion molecules are induced by inflammatory mediators released from leucocytes and endothelium, and these in turn are induced by high serum cholesterol levels or complement fragments. Leucocytes which have adhered to the endothelium are chemo-attracted into the vessel wall by cytokines produced by early arriving leucocytes or by low density lipoprotein which has passively passed into the wall, in the process being trapped and oxidised. The oxidised low density lipoprotein is taken up by scavenger receptors (which are not subject to down-regulation) on both macrophages and smooth muscle cells. The overaccumulation of lipid is toxic to the cells and they die contributing to the central necrotic core. The macrophages and T-lymphocytes produce substances which induce smooth muscle cells of the artery wall to change from a 'contractile' (high volume fraction of myofilaments [Vvmyo]) to a 'synthetic' (low Vvmyo) phenotype. In this altered state they respond to growth factors released from macrophages, platelets, regenerating endothelial cells and smooth muscle cells; produce large amounts of matrix; express lipoprotein scavenger receptors; express adhesion molecules for leucocytes; and express HLA-DR following exposure to the T-lymphocyte product, IFN-delta, suggesting that they can become involved in a generalised immune reaction.