Coordination of intra- and extracellular signaling during
salinity stress
Von Willebrand factor A domain-containing (VFA) proteins are
extracellular proteins involved in cell-cell adhesion and signaling as
well as blood clot formation after injury. VFA domain-containing protein
8 (VFA8) was the third most highly regulated protein (FC=6.41, p=.0001)
while VFA/sushi/EGF and pentraxin domain-containing protein 1 was the
second most significantly regulated mRNA (FC=-17.4, p=1.02E-6). This
opposite regulation pattern suggests that different VFA proteins are
associated with renal function in FW versus BW acclimated tilapia. In
one study, red blood cell count was significantly reduced in O.
niloticus exposed to 12ppt saline water for 14 days (Elarabany,
Bahnasawy, Edrees, & Alkazagli, 2017). Osmotic stress is known to
induce erythrocyte cell death by opening
Ca2+-permeable cation channels, increasing cytosolic
Ca2+ activity and triggering erythrocyte apoptosis
(Lang et al., 2003). Therefore, BW acclimation may increase erythrocyte
cell death in the kidney. This conclusion is supported by the
significant reduction in hemoglobin subunit beta-1 (FC=-7.27, p=.0051)
and increase in haptoglobin (FC=2.56, p=.03), which neutralizes the
oxidative effects of free heme groups. Furthermore, VFA8 has been
reported to translocate to the inner membrane of mitochondria in
response to calcium-induced signaling and to influence mitochondrial
energy metabolism (Luo et al., 2020). These data suggest that VFA
proteins are involved in linking extracellular osmotic stress sensing
with intracellular responses such as increased mitochondrial energy
production.