Megaloblastic anemia, diabetes, and sensorineural deafness characterize the autosomal recessive human disorder, Thiamine-Responsive Megaloblastic Anemia syndrome (TRMA). TRMA is due to mutations of the human SLC19A2 gene, which encodes a high-affinity thiamine membrane transporter. The murine Slc19a2 knock-out (-/-) model (

Fleming et al,
Mol Gen Metab
;
80
(
2003
),
234
–241
) develops thiamine-dependent reticulocytopenia without megaloblastic anemia or sideroblasts, but the whole animal knockouts become ill in thiamine-depleted settings, which limit investigation of erythropoiesis. Here we investigate, by bone marrow transplantation experiments, whether the erythropoietic defect is cell-intrinsic and correlated with the correct function of Slc19a2. We conducted this study by transplanting C57BL/6J-GPIb Slc19a2−/− (−/−) or wild type (+/+) bone marrow into C57BL/6J-GPIa wild type (+/+) mice. These congenic strains were chosen to distinguish host and donor cells by GPI isozymes. After host irradiation (525 cG for 2 doses), we injected 4 X106 donor marrow cells retro-orbitally. After engraftment, confirmed by GPIa/b assay (>60 days), we switched animals to either 2mg/kg chow thiamine diet (control) or 0 mg/kg thiamine (normal mouse chow is 22 mg/kg thiamine). The transplant experiments were carried in duplicate and included a total of 53 transplant recipient mice of both sexes. After 24-day diet both +/+ and −/− groups on 0 mg/kg thiamine diet lost weight (~28%). Blood parameters changed unequally. After 24 days on 0 mg/kg thiamine diet mice transplanted with −/− bone marrow reveled a significant increment of reticulocyte mean cell volume (MCV) (23% with P< 0.01) together with a relevant decrease of red blood cell count (46% and P< 0.01). A severe leukopenia diet correlated was also observed in both groups of mice on thiamine-depleted diet. The blood parameters of mice on 2-mg/kg diet did not reveal significant changes along the entire diet period. These results confirm the involvement of Slc19a2 membrane transporter in the impaired thiamine cell uptake and allow us to say that the erythropoietic defect we first observed in Slc19A2 KO mice is not only diet related, but due to a cell-intrinsic marrow defect.

Tables. Peripheral blood parameters of bone marrow transplanted mice at baseline and after 24 days on depleted thiamine diet.

BASELINE

DonorWBCRBCMCV Retic
−/− mean (StDev) 20.41 (4.23) 10.5 (3.46) 61.83 (2.38) 
+/+ mean (StDev) 20.63 (2.36) 9.24 (1.45) 67.4 (3.03) 
 P 0.9140 0.4257 0.0136 
DonorWBCRBCMCV Retic
−/− mean (StDev) 20.41 (4.23) 10.5 (3.46) 61.83 (2.38) 
+/+ mean (StDev) 20.63 (2.36) 9.24 (1.45) 67.4 (3.03) 
 P 0.9140 0.4257 0.0136 
View Large

24 days on 0 mg/kg thiamine diet

DonorWBCRBCMCV retic
St Dev = Standard Deviation P = probability 
−/− mean (StDev) 8.53 (1.75) 6.79 (1.65) 76.18 (1.24) 
+/+ mean (StDev) 6.51 (3.16) 6.09 (1.37) 65.23 (5.04) 
 P 0.3232 0.0321 0.0011 
DonorWBCRBCMCV retic
St Dev = Standard Deviation P = probability 
−/− mean (StDev) 8.53 (1.75) 6.79 (1.65) 76.18 (1.24) 
+/+ mean (StDev) 6.51 (3.16) 6.09 (1.37) 65.23 (5.04) 
 P 0.3232 0.0321 0.0011 
View Large

Topics:
anemia, thiamine, weight reduction, diet, cisplatin/methotrexate/vinblastine protocol, mean corpuscular volume analyses, megaloblastic anemia, thiamine-responsive, with diabetes mellitus and sensorineural deafness, megaloblastic anemia, membrane transport proteins, bone marrow transplantation

Author notes

Corresponding author

2005, The American Society of Hematology
2005
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