[Thesis]. Manchester, UK: The University of Manchester; 2018.
Mucopolysaccharidosis IIIA (MPSIIIA) is a paediatric neurological lysosomal storage
disease, characterised by a deficiency in the lysosomal hydrolase sulfo-glucosamine
sulfo-hydrolase. This leads to the accumulation of partially degraded, highly sulphated
heparan sulphate, resulting in widespread cellular and tissue dysfunction, predominantly
in the CNS. Patients present with onset of symptoms early in the first decade of life,
with progressive failure to achieve developmental milestones and severe behavioural
changes, including hyperactivity, sleep disturbances and aggression. As the disease
progresses, cognitive and later motor function decline ensue, with premature death
in the second decade of life. There are no treatments currently available. Although
we and others have previously focussed on delivering replacement enzyme, therapies
targeting other aspects of childhood disease, notably abnormal behaviour and cognitive
decline are warranted. Targeting brain inflammation represents a potential clinical
We set out to understand how disease pathology can lead to abnormal phenotypes, and
particularly to understand if IL-1, a major pro-inflammatory mediator has a central
role in neuroinflammation in MPSIIIA.
MPSIIIA disease neuropathology involves multiple factors including heparan sulphate
storage, storage of secondary substrates, and neuroinflammation. We first set out
to unravel the role of storage substrates in inflammation. We demonstrated 2-O sulphation
of MPSIIIA heparan sulphate was essential for inflammatory priming via the toll-like
receptor 4/CD14/MD2 complex. In conjunction with heparan sulphate, MPSIIIA secondary
storage substrates, cholesterol, amyloid beta and ATP activated the NLRP3 inflammasome
and initiated secretion of IL-1beta in vitro.
Using lentiviral-mediated haematopoietic stem cell gene therapy (HSCT) to drive human
interleukin-1 receptor antagonist in a mouse model of MPSIIIA, we were able to attenuate
the IL-1 immune response, which resulted in sustained reduced brain microgliosis and
astrogliosis, and complete correction of hyperactivity and working memory defects.
The contribution of IL-1 to abnormal behaviour associated with MPSIIIA was confirmed
in a MPSIIIA x IL-1R1-/- mouse model.
We compared two levels of human IL-1Ra overexpression via LV.IL1RN vector mediated
HSCT in the MPSIIIA mouse model in order to determine whether there was a toxicity
limit associated with IL-1Ra overexpression. We compared a maximal dose of LV.IL1RN
against a lower dose of LV.IL1RN already known to be therapeutic and well tolerated.
High dose LV.IL1RN HSCT demonstrated myelotoxicity, reduced leukocyte trafficking
to the brain and liver and hyper-activation of resident immune cells. High dose LV.IL1RN
HSCT was unable to correct the behavioural abnormalities associated with MPSIIIA.
Lastly, we investigated the physician observation that MPSIII patients suffering from
infection appear to deteriorate more rapidly post-recovery, with respect to cognitive
decline. Several groups have documented stepwise declines in cognition following recovery
from a systemic infection, in patients and animal models with Parkinsons disease,
Amyotrophic lateral sclerosis, Alzheimers disease and Prion disease. We show that
the viral mimetic poly(I:C) amplified sickness behavioural responses, exacerbated
systemic and CNS cytokine expression, in particular IL-1beta and induced neuronal
loss in MPSIIIA mice but not WT. We also showed that repeat poly(I:C) challenges in
MPSIIIA animals exacerbated existing working memory deficits and hyperactive behaviour,
and suggest that systemic infections represent a major risk factor for the progression
of cognitive decline in MPSIIIA.
Our findings indicate that IL-1 is a major driver of neuroinflammation and cognitive
decline in MPSIIIA, and IL-1Ra is a potential anti-inflammatory therapeutic for neuro-inflammatory