Transcript The four major types

Removing toxic aggregates
that our cells can’t break down
Aubrey de Grey
Department of Genetics, University of Cambridge
Email: [email protected]
Website: http://www.gen.cam.ac.uk/sens/
The lysosome:
the cell’s garbage disposal
machinery of last resort
Amino
acids
R
P
Lysosome
?
M
The problem: the lysosome is
not omnipotent
Liver’s solution: exocytosis
Lysosome
Lysosome
Not done elsewhere: kidneys would suffer?
All other cells’ “solution”:
sequestration
Obviously fails eventually
Cellular function impaired
Cell becomes toxic
Cell dies
Lysosomal junk:
The four major types
1) Lipofuscin. Universal marker of postmitotic
cell aging; reaches 10% of total cell mass in
heart and motor neurons. No clear proof of
pathogenesis, but in vitro evidence is strong
Lysosomal junk:
The four major types
2) A2E -- weird molecule created by reaction of
the membrane lipid phosphatidylethanolamine
with the photoreceptor pigment retinal. More
or less proven to be pathogenic: causes agerelated macular degeneration.
Lysosomal junk:
The four major types
3) Hyperphosphorylated tau in neurons. Widely
believed to be a major cause of Alzheimer’s
disease. Similar aggregates form in other
neurodegenerative diseases and normal aging.
Lysosomal junk:
The four major types
4) Oxidised (etc) cholesterol and cholesteryl
esters (oxysterols) in arterial macrophages.
Causes them to become “foam cells”, then
fatty streaks, and eventually atherosclerotic
plaques.
Why don’t graveyards fluoresce?
de Grey 2002, Trends in Biotechnology 20:452-455
These (often fluorescent) materials do not accumulate in
nature, even in areas rich in the remains of animals that
produce them. Thus, something degrades them. They
are energy-rich, so micro-organisms could live off them.
Bacterial strains exist with astonishingly varied catabolic
activities, and are being used by many groups for
bioremediation purposes. They degrade rubber, TNT,
PCBs, dioxin, ... Some fungi are similarly versatile.
Can micro-organisms capable of degrading
lysosomal junk be isolated from the soil???
Some FAQs
Q: Aren’t foam cell lysosomes mainly native cholesterol?
A: Yes - the major lysosomal component is not necessarily
the culprit - the culprit may impair lysosomal trafficking
of normally benign things
Q: Won’t we need an awful lot of different enzymes?
A: Probably not - degradation is synergistic - one step will
often form a substrate for an enzyme we already have
Q: What about immune rejection?
A: Same problem/solutions as for normal gene therapy
Steps to biomedical application
1) Isolate competent strains; select by starvation
2) Identify the enzymes (mutagenesis, chemistry, genomics)
3) Make lysosome-targeted transgenes, assay cell toxicity
4) Assay competence in vitro (more mutagenesis/selection)
5) Construct transgenic mice, assay toxicity in vivo
6) Assay competence in disease models (apoE-/- mice, etc.)
7) Test in humans as for lysosomal storage diseases
Funding: the story so far
2001, 2002: Kronos deem it too “sciencey” :-(
2003: Archer wows NIA officials at IABG10 :-)
2004: “SENS 5” (July 26th, NIA offices, Bethesda)
Jay Jerome: atherogenic junk
Ralph Nixon: neurotoxic junk
Janet Sparrow: ophthalmotoxic junk
Ana Maria Cuervo: gene engineering for lysosomal targeting
Roscoe Brady: protein engineering for lysosomal targeting
Bruce Rittmann, Perry McCarty, Pedro Alvarez: biorem.
Fingers crossed….