Atherosclerosis is a disease process that reduces arterial blood vessel calibre, and is a major
cause of morbidity and mortality in the industrialised world. Decreased vascular flow
reduces tissue viability, resulting in cardiac, cerebrovascular, renovascular and peripheral
arterial diseases. Inflammatory leukocyte responses underlie atherosclerosis. Clinical
epidemiological data show that pro-atherogenic factors, including hyperlipidaemia,
uncontrolled hypertension and cigarette smoking increase vascular inflammation, elevating
an individual's risk of developing atherosclerosis. Local inflammation may alter leukocyte
phenotype, function and survival, activating resident atherosclerotic plaque macrophages,
and exacerbating vascular injury.
This thesis aimed to assess whether monocyte survival, phenotype and gene transcription
alters in response to pro-atherogenic and pro-inflammatory micro-environmental stimuli
including oxidised low-density lipoprotein and cyclopentenone prostaglandins, metabolites
of arachidonic acid.
Oxidised low-density lipoproteins and cyclopentenone prostaglandins accelerated monocyte
apoptosis, in serum-free conditions, in a concentration dependent manner. Cyclopentenone
prostaglandin-induced monocyte apoptosis was caspase dependent, but oxidised low-density
lipoprotein-induced monocyte apoptosis only partially caspase-dependent. Monocyte
apoptosis appeared to be independent of the nuclear receptor and transcriptional controller
peroxisome proliferator receptor gamma PPARy. Arachidonate-induced monocyte apoptosis
appeared to be caused by a disruption of NF-kB mediated signalling. Monocyte apoptosis
appeared inversely related to maturation, with nai've undifferentiated monocytes being more
susceptible to programmed cell death than committed macrophages.
Monocyte transcriptional responses to oxidised LDL were assessed using gene mini-arrays.
Genes for CD47 and CD1 la showed significant levels of variation on the array, with CD1 la
changes being confirmed by polymerase chain reaction assessment.
Monocyte surface molecular changes induced by low-density lipoprotein were directly
assessed by indirect immuno-labelling and flow cytometric analysis. Oxidised low-density
lipoprotein elevated monocyte surface CD54 in early suspension culture, but then caused a
down-regulation of CD54 in prolonged adherent culture. Oxidised low-density lipoprotein
diminished monocyte surface expression of CD1 lb and CD1 lc in a manner dependent upon
adhesion and maturation. CD49d expression appeared to be reduced by oxidised low-density
lipoprotein in mature adherent monocytes. Early marginal reductions in CDlla expression
were not seen in more mature monocytes.
Pro-atherogenic and pro-inflammatory micro-environmental influences thus appeared to
regulate monocyte viability and gene transcription, although this is not necessarily reflected
at a protein level. Monocyte surface phenotype appeared to alter following exposure to
modified lipoproteins, in a manner that may cause changes in monocyte mobility. These
findings may contribute to our understanding of cell death in atherosclerotic lesions, and
potential limitations on cell mobility out of atherosclerotic plaque.