Effects of Microgravity on the Haemopoietic System: A Study on Neocytolysis (Neocytolysis)
Research Area: Cellular Biology
Expedition(s): 14- 16
Principal Investigator(s): ● Angela Rizzo, PhD, University of Udine, Udine, Italy
RESEARCH OBJECTIVES
The objective of the Effects of Microgravity on the Haemopoietic System: A Study on
Neocytolysis (Neocytolysis) experiment is to better characterize the neocytolytic process in
space and investigate some variations of young red cells mediated by exposure to microgravity,
which could explain their apparently selective lysis. This study could strengthen the hypothesis
that neocytolysis is involved in a number of hematologic disorders.
RESULTS
After spaceflight, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular
hemoglobin concentration, red blood cell counts, and hematocrit values were not significantly
different from those measured before flight. In 3 astronauts the reticulocyte counts were lower
than before the flight. The hematochemical analysis disclosed a mean increase of 1,54+1,1 times in
ferritin plasma level in 3 subjects. As expected, the percentage of recently generated red blood
cells (young and a fraction of middle aged red blood cells) was decreased after the flight.
Moreover, the percentage of middle aged, old and, to a greater extent, young red blood cells,
exposing phosphatydilserine on the outer membrane leaflet was increased. Finally, the young cells
had lost viability, as measured by calcein fluorescence, and the expression of CD55 and CD47
proteins by neocytes was decreased both in term of the number of positive cells (from 91.25+7
and 96+2.7 to 86.35+4.4 and 87 +8.58, respectively), and in term of level of expression
(fluorescence intensity). No significant changes were observed in control subject’s red blood cell
population.
The consistency in the
differences observed for
some of the
hematological
parameters and red blood
cell features, prompt
some conclusions,
although the number of
subjects analyzed in this study was small. Erythrocyte destruction likely occurred during the
spaceflight, as indicated by the increase in plasma ferritin. Hemolysis occurred most likely due
to destruction of neocytes, because young erythrocyte counts in blood samples drawn after the
flight were lower than before the flight. The exposure of phosphatydilserine, the loss of viability
and the decreased expression of CD47 in some of the still surviving young red blood cells
support this view, indicating that an “apoptotic-like” phenotype could trigger ingestion by
Healthy red blood cells (upper left) are smooth and round. Hemolytic red blood
cells (lower right). The Cleveland Clinic, Cleveland, Ohio image.