Microglial opsonins and extracellular chaperones
Lead Research Organisation:
University of Cambridge
Department Name: Biochemistry
Abstract
PhD project strategic theme: Bioscience for an integrated understanding of health
Microglia are brain-resident macrophages that are known to: i) shape neuronal circuits during development by phagocytosing excess synapses and neurons, ii) protect against brain infection, damage and amyloid, by phagocytosing pathogens, debris and aggregates, and iii) contribute to some brain pathologies via excessive inflammation or phagocytosis. There is evidence that these processes contribute to: autism, schizophrenia, stroke, brain trauma, infections, neurodegenerative diseases and brain ageing.
Phagocytosis is the engulfment and digestion of extracellular particles, including other cells. Opsonins are normally soluble proteins, which when bound to particles such as cells encourage phagocytes to phagocytose these. It is known that some, previously identified opsonins, are strongly upregulated by inflammation. This project would look to identify and characterise novel candidate opsonins, such as APOE and clusterin (APOJ). These may accumulate on the surfaces of dead, damaged or stressed neurons or synapses, and promote phagocytosis of these by microglia. We would test candidate opsonins by investigating whether they bind to synapses or neurons in different conditions, whether they stimulate microglial phagocytosis of these, and whether blocking or knocking them down reduces phagocytosis.
"Nopsonins" are negative opsonins that inhibit phagocytosis of particles/cells that they are bound to. Candidate nopsonins include progranulin and sTREM2. We will test candidate nopsonins by similar means to that for opsonins above.
Extracellular chaperones are proteins that bind misfolded proteins (in the extracellular space) to promote their re-folding, proper folding or degradation. Brain ageing and multiple neurodegenerative diseases involve the spread of misfolded proteins in the extracellular space, including amyloid beta (AB), tau, a-synuclein and prions. This project will build on work previously carried out in the laboratory, investigating several proteins, including calreticulin, galectin-3 and sTREM2, released from microglia, that increase or decrease AB aggregation and/or microglial activation.
Calreticulin is an ER-resident chaperone. The lab has shown that activated microglia release calreticulin into the culture medium. And it has been reported that calreticulin can bind to the hydrophobic C-terminal of AB, and that calreticulin is bound to AB in human CSF. During my rotation, I obtained evidence that calreticulin potently inhibits AB aggregation. We would further investigate: how calreticulin affects AB aggregation, how calreticulin affects AB neurotoxicity, and how calreticulin affects AB microglial activation. We would further investigate the role of calreticulin on AB in vivo, and the effects of extracellular calreticulin on tau, a-synuclein and prions.
TREM2 is an innate immune receptor expressed on microglia. Loss-of-function mutations are associated with increased risk of AD. TREM2 undergoes proteolytic processing, releasing a soluble form sTREM2 found in human CSF. Evidence from the lab suggests that wild-type sTREM2 may protect against AD by blocking AB aggregation, while AD risk-associated variant, R47H, may predispose to AD by lacking this protective function, and potentially folding AB into neurotoxic forms. This project will further characterise the effect of sTREM2 on AB aggregation and microglial behaviour.
There is further scope to identify additional novel microglial extracellular chaperones and opsonins, to shed light on microglial involvement in neuroinflammation and neurodegeneration and aid future development of effective therapeutics.
Microglia are brain-resident macrophages that are known to: i) shape neuronal circuits during development by phagocytosing excess synapses and neurons, ii) protect against brain infection, damage and amyloid, by phagocytosing pathogens, debris and aggregates, and iii) contribute to some brain pathologies via excessive inflammation or phagocytosis. There is evidence that these processes contribute to: autism, schizophrenia, stroke, brain trauma, infections, neurodegenerative diseases and brain ageing.
Phagocytosis is the engulfment and digestion of extracellular particles, including other cells. Opsonins are normally soluble proteins, which when bound to particles such as cells encourage phagocytes to phagocytose these. It is known that some, previously identified opsonins, are strongly upregulated by inflammation. This project would look to identify and characterise novel candidate opsonins, such as APOE and clusterin (APOJ). These may accumulate on the surfaces of dead, damaged or stressed neurons or synapses, and promote phagocytosis of these by microglia. We would test candidate opsonins by investigating whether they bind to synapses or neurons in different conditions, whether they stimulate microglial phagocytosis of these, and whether blocking or knocking them down reduces phagocytosis.
"Nopsonins" are negative opsonins that inhibit phagocytosis of particles/cells that they are bound to. Candidate nopsonins include progranulin and sTREM2. We will test candidate nopsonins by similar means to that for opsonins above.
Extracellular chaperones are proteins that bind misfolded proteins (in the extracellular space) to promote their re-folding, proper folding or degradation. Brain ageing and multiple neurodegenerative diseases involve the spread of misfolded proteins in the extracellular space, including amyloid beta (AB), tau, a-synuclein and prions. This project will build on work previously carried out in the laboratory, investigating several proteins, including calreticulin, galectin-3 and sTREM2, released from microglia, that increase or decrease AB aggregation and/or microglial activation.
Calreticulin is an ER-resident chaperone. The lab has shown that activated microglia release calreticulin into the culture medium. And it has been reported that calreticulin can bind to the hydrophobic C-terminal of AB, and that calreticulin is bound to AB in human CSF. During my rotation, I obtained evidence that calreticulin potently inhibits AB aggregation. We would further investigate: how calreticulin affects AB aggregation, how calreticulin affects AB neurotoxicity, and how calreticulin affects AB microglial activation. We would further investigate the role of calreticulin on AB in vivo, and the effects of extracellular calreticulin on tau, a-synuclein and prions.
TREM2 is an innate immune receptor expressed on microglia. Loss-of-function mutations are associated with increased risk of AD. TREM2 undergoes proteolytic processing, releasing a soluble form sTREM2 found in human CSF. Evidence from the lab suggests that wild-type sTREM2 may protect against AD by blocking AB aggregation, while AD risk-associated variant, R47H, may predispose to AD by lacking this protective function, and potentially folding AB into neurotoxic forms. This project will further characterise the effect of sTREM2 on AB aggregation and microglial behaviour.
There is further scope to identify additional novel microglial extracellular chaperones and opsonins, to shed light on microglial involvement in neuroinflammation and neurodegeneration and aid future development of effective therapeutics.
