Low-dose busulphan conditioning and neonatal stem cell transplantation preserves vision and restores hematopoiesis in severe murine osteopetrosis.
OBJECTIVE
Infantile malignant osteopetrosis is a fatal disease caused by lack of functional osteoclasts. In most of patients, TCIRG1, encoding a subunit of a proton pump essential for bone resorption, is mutated. Osteopetrosis leads to bone marrow failure and blindness due to optic nerve compression. Oc/oc mice have a deletion in Tcirg1 and die around 3 to 4 weeks, but can be rescued by neonatal stem cell transplantation (SCT) after irradiation conditioning. However, as irradiation of neonatal mice results in retinal degeneration, we wanted to investigate whether conditioning with busulphan prior to SCT can lead to preservation of vision and reversal of osteopetrosis in the oc/oc mouse model.


METHODS
Pregnant dams were conditioned with busulphan and their litters transplanted with 1 x 10(6) normal lineage-depleted bone marrow cells intravenously or intraperitoneally. Mice were followed in terms of survival and engraftment level, as well as with peripheral blood lineage analysis, bone and eye histopathology and a visual-tracking drum test to assess vision.


RESULTS
Busulphan at 15 mg/kg was toxic to oc/oc mice. However, six of seven oc/oc mice conditioned with busulphan 7.5 mg/kg survived past the normal lifespan with 10% engraftment, correction of the skeletal phenotype, and normalization of peripheral blood lineages. Busulphan, in contrast to irradiation, did not have adverse effects on the retina as determined by histopathology, and 8 weeks after transplantation control and oc/oc mice retained their vision.


CONCLUSIONS
Low-dose busulphan conditioning and neonatal SCT leads to prolonged survival of oc/oc mice, reverses osteopetrosis and prevents blindness even at low engraftment levels.
Askmyr
Maria
M
Molecular Medicine and Gene Therapy, Lund Stem Cell Center, University Hospital of Lund, Lund, Sweden.
Holmberg
Johan
J
Flores
Carmen
C
Ehinger
Mats
M
Hjalt
Tord
T
Richter
Johan
J
D000818:Animals; D000831:Animals, Newborn; D001766:Blindness / Q000209:etiology / Q000235:genetics / Q000378:metabolism / Q000628:therapy; D002066:Busulfan / Q000009:adverse effects / Q000494:pharmacology*; D004195:Disease Models, Animal; D006410:Hematopoiesis / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D007231:Infant, Newborn; D051379:Mice; D019653:Myeloablative Agonists / Q000009:adverse effects / Q000494:pharmacology*; D010022:Osteopetrosis / Q000150:complications / Q000235:genetics / Q000378:metabolism / Q000628:therapy*; D033581:Stem Cell Transplantation; D019172:Transplantation Conditioning; D025262:Vacuolar Proton-Translocating ATPases / Q000235:genetics; D014785:Vision, Ocular / Q000187:drug effects* / Q000235:genetics
C484226:Atp6ap1 protein, mouse; D019653:Myeloablative Agonists; C472421:TCIRG1 protein, human; D025262:Vacuolar Proton-Translocating ATPases; D002066:Busulfan