Bolivian Aymara Natives with Chronic Mountain Sickness Have Autonomous BFU-E Growth

Abstract

Background Erythrocytosis / polycythemia is divided into primary and secondary. Primary polycythemia can be either acquired; i.e. polycythemia vera (PV) due to somatic JAK2 mutation, or congenital due to germ-line DNA changes (erythropoietin (EPO) receptor and VHL mutations in Chuvash polycythemia). These mutations are expressed within erythroid progenitors, drive increased erythropoiesis and are detected by hypersensitive or autonomous EPO BFU-E responses. In contrast, secondary erythrocytosis (SE), such as seen with cardiopulmonary pathologies, is driven by the circulating EPO. Chronic mountain sickness (CMS) is characterized by high altitude pathological erythrocytosis and by cognitive and neurological impairments. CMS is found in subjects living in high altitude (2500 meters and higher). In La Paz, Bolivia, (3600m) there is 7% incidence of CMS erythrocytosis. Some human populations (Tibetans, Andean Quechuas and Aymaras, and Ethiopians) are adapted to very high altitudes and their adapted phenotypes and, in some instances, evolutionarily selected haplotypes, have been reported. Whole genome was evaluated in Andeans and two genes, SENP1 and ANP32D were found to be evolutionarily selected and correlated with presence or absence of erythrocytosis. The genes down-regulation in hypoxia had survival benefit in Drosophila ortholog (1).SENP1 desumoylate GATA-1 and other regulatory proteins and is critical for definitive erythropoiesis (2,3). Here we evaluated native Aymara La Paz dwellers with three types of polycythemia: CMS, SE secondary to cardiopulmonary disease, and PV, by clinical studies and by in vitro evaluation of erythroid progenitors, and compared them to non-polycythemic subjects. Patients and Methods Complete blood count was performed by automatic hematologic counter (Micro 60, USA). Serum EPO was measured by Elisa (R&D System, USA) and JAK2V617F mutation analysis by PCR assay. Erythroid progenitors were isolated by density gradient centrifugation and cultured in methylcellulose medium with and without EPO (Stem Cell technologies, Canada) at 370 C and 5 % CO2. BFU-E colonies reading was carried out according to standardized criteria at 7 and 14 days. Results Table. Normal Control(n=10) CMS (n=15) Secondary Erythrocytosis(n=10) PolycythemiaVera (n=5) 1.Gender M/F 10/0 15/0 10/0 3/2 Age (range) 42 (40-47) 48 (29-58) 53 (34-72) 67 (42-74) Hb g/dl (SD) 16.2 (+ 0.9) 20.3 (+ 0.9) 22.8 (+ 1.4) 20.0 (+ 2.5) Ret % (SD) 1.3 (+ 0.1) 2.9 (+ 1.3) 3.6 (+ 1.2) 2.1 (+ 0.3) WBC /ul (SD) 6300 (+ 1600) 7200 (+ 1900) 6600 (+ 1700) 16600 (+ 4800) PLT 103 ul (SD) 273 (+ 80) 229 (+ 58) 193 (+ 54) 604 (+ 177) sEPO mUI/ml (SD) 10.0 (+ 3.9) 10.5 (+ 2.2) 82.9 (+ 30.4) 3.0 (+ 1.2) JAK2 V617F, No. (%) 0 (0) 0 (0) 0 (0) 100 Apoptosis Normal Delayed Normal Delayed BFU-E: EEC 0 (0-0) 10 (2-25) 0 (0-0) 45 (25-70) References: 1. Yu L et al. J Exp Med., 2010, 207:1183. 2. Sharma D et al. Cell Report, 2013, 3:1640. 3. Zhou D et al. Am J Hum Genet. 2013, 93:452. 4. Kapralova K et al. Blood. 2014,123:391 Conclusions a) Endogenous erythroid colony (EEC) are present in Aymaras with CMS, indicating primary polycythemia. b) Endogenous EECs are higher in PV than in CMS. c) CMS subjects have normal serum EPO levels. d) The role of SENP1, and hypoxia-regulated RUNX1 and NF-E2 (4) that promote erythropoiesis, is being interrogated in native erythroid cells. e) It remains to be determined if the autonomous BFU-E growth is specific for Aymara's CMS or present in CMS individuals of other ethnicities. Disclosures No relevant conflicts of interest to declare.

“What We Know and What We Do Not Know about Evolutionary Genetic Adaptation to High Altitude Hypoxia in Andean Aymaras”

“…Evolutionary adaptations to high altitude in these geographically separated populations differ in Hb concentrations [ 3 , 4 , 5 ]. Tibetans living at 4000 m have similar hemoglobin (Hb) levels to individuals living at sea level, whereas Hb levels of Bolivian Andean Aymaras living at 4000 m are increased [ 6 , 7 , 8 ] and this difference is the subject of our report.…”

“…In contrast, the Andean Aymaras did not appear to have evolved mechanisms to modify erythropoiesis but have adapted to exist with higher hemoglobin concentrations than individuals dwelling at sea level. This different phenotype is likely due to the positive selection of different genes, but it also may reflect the influence of a smaller number of generations and a shorter period of exposure to high altitudes by Aymaras [ 6 , 7 ].…”

“…The prevalence of high altitude erythrocytosis differs according to the region, the duration of residence and the altitude of residence, and specific evolutionary adaptations unique to a particular ethnic group. High-altitude erythrocytosis prevalence differs greatly among high mountain dwellers; while it is found in only 1.2% of Native Tibetans, it is reported to be present in 5.6% of Han Chinese and 15.6% of Aymara highlanders [ 6 , 7 ]. Hemoglobin levels in Aymaras vary and generally increase with increasing altitudes.…”

“…In Santa Cruz (400 m) Hb levels range from 12 to 15 g/dL in women and 13 to 16 g/dL in men. In La Paz (4000 m), Hb levels range from 14 to 17 g/dL in women and 15 to 18 g/dL in men; and in Chorolque (5000 m), Hb levels range from 15 to 18 g/dL in women and 16 to 19 g/dL in men [ 6 , 7 ].…”