| dc.description.abstract | Retinal degenerative diseases, such as retinitis pigmentosa (RP) and age-related
macular degeneration (AMD), represent a leading cause of incurable blindness
worldwide. RP is a genetically inherited retinal degeneration with causative mutations
in over 70 genes which affects 1:4,000 individuals worldwide. AMD is a multifactorial
disease with contributions from both genetic and environmental risk factors. The
prevalence of AMD is growing, in part due to an ageing population, and it is estimated
that by 2040, 288 million individuals will be affected by this disease. Despite varying
pathophysiology, death of photoreceptor cells represents a common endpoint and
cause for many retinal degenerative diseases. There is a current lack of therapeutic
strategies to prevent photoreceptor cell death and preserve vision.
The Toll-like receptor (TLR) adaptor protein Sterile α- and armadillo motif-containing
protein (SARM1) has in recent years been identified as an inducer of axonal
degeneration and neuronal cell death. SARM1 induces degeneration of axons through
enzymatic cleavage of nicotinamide adenine dinucleotide (NAD+), a conserved function
present in bacterial and plant Toll/IL-1 receptor (TIR) domain containing proteins. Our
lab and subsequently another group, have demonstrated a role for SARM1 in induction
of photoreceptor cell death in models of retinitis pigmentosa and Leber congenital
amaurosis, respectively. Our aim was to determine whether SARM1 mediated
photoreceptor degeneration was a feature of non-inherited retinal degeneration. In an
oxidative stress induced model of retinal degeneration, injection of sodium iodate
(NaIO3), deletion of SARM1 was shown to delay photoreceptor degeneration. Thus,
indicating that SARM1 mediated photoreceptor cell death may be a common
degenerative mechanism across a range of diseases.
SARM1 regulates a chemokine response in neurons following axonal injury, which
recruits innate immune cells to the cell body of the injured neuron. The migration of
immune cells to the sub-retinal space and photoreceptor layer is implicated in the
pathogenesis of many retinal degenerative diseases and we aimed to determine
whether this SARM1 regulated chemokine response is conserved in photoreceptors.
Our initial aim was to assess this in our mouse model of retinitis pigmentosa (Rho-/-).
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We observed decreased microglia migration to the photoreceptor layer of the retina in
Rho-/- mice lacking SARM1. However, during the course of our research it was
discovered that the initial strain of Sarm1-/- mice, which were used in our previous work
and to generate the Rho-/-Sarm1-/- strain, contained large regions of DNA around the
SARM1 locus of 129 strain origin. To account for any potential confounding effects of
these passenger mutations we utilised a new SARM1 deficient mouse strain generated
using CRISPR/Cas9, Sarm1-/-CR. In the early phase of NaIO3 induced retinal degeneration
there is decreased cell infiltration into the retina coupled with decreased levels of the
chemokine CCL2 and the damage associated cytokine IL-33 in the retina of Sarm1-/-CR
mice. We also observed decreased accumulation of F4/80- monocytes in the retina of
Sarm1-/-CR mice during a later phase of NaIO3 induced degeneration.
Lastly, we aimed to assess the potential therapeutic benefit of targeted SARM1
knockdown in the retina using antisense oligonucleotides (ASOs). Here we have
optimized a strategy for intravitreal delivery of ASO which provides robust SARM1
mRNA and protein knockdown, while maintaining retinal homeostasis. ASO mediated
SARM1 knockdown decreased photoreceptor degeneration in the NaIO3 model of
retinal degeneration, recapitulating our observations from SARM1 deficient mice.
Together the work presented in this PhD thesis demonstrates that SARM1 induces
photoreceptor cell death in response to oxidative stress and may regulate a
photoreceptor chemokine response in the retina. Additionally, we have shown that
targeting of SARM1 using ASO is a potential therapeutic strategy for the treatment of
retinal degenerative disease. | en |
