Endogenous brain erythropoietin is a potent sex-specific respiratory stimulant in adult and newborn mice

Abstract

We tested the hypothesis that endogenous brain Epo is a respiratory stimulant. Adult (3 mo) and newborn (10 days) male and female mice received an intracisternal (cisterna magna) injection of soluble Epo receptor (sEpoR; competes with EpoR to bind Epo; 50 μg/ml) or vehicle (0.1% BSA in PBS). Twenty-four hours after injection, we used whole body plethysmography to record minute ventilation (V̇e) tidal volume (VT), respiratory frequency (fR), O2 consumption (V̇o2), and CO2 production (V̇co2) under normoxia and progressive exposure to hypoxia (12-10-6% O2; 10 min each). In adult male and female mice sEpoR decreased normoxic V̇e (-25%), due to a decrease of VT in males and fR in females. Moreover, sEpoR injection decreased the ventilatory response to 12% O2, assessed as V̇e/V̇o2 or V̇e/V̇co2, in male but not in female mice. In newborn male and female mice sEpoR decreased V̇e (-37% in males, -59% in females) and VT (-38% in males, -47% in females) in normoxia and fR in females. During hypoxia, sEpoR decreased V̇e/V̇o2 and V̇e/V̇co2 in mice of both sexes. Upon extreme hypoxia (6% O2), the newborn mice treated with sEpoR showed respiratory depression, signs of asphyxia (gasping) and a high mortality rate in males and females. We concluded that endogenous brain Epo is a potent respiratory stimulant under normoxia and hypoxia in adult and newborn mice. Because sex-specific effects are different in newborn male and female, sex steroids secreted at different ages mice appear to modulate the effects of Epo on respiratory regulation in normoxia and in response to hypoxia.

Chronic overexpression of cerebral Epo improves the ventilatory response to acute hypoxia during the postnatal development

“…One important difference observed between the work in which the sEpoR was administrated (Ballot et al, 2015) and the present study is that sEpoR was able to significantly decrease the basal ventilation (normalized by the oxygen consumption) while the Epo overexpression did not. Comparable outcomes were obtained in Tg21 adult mice that showed similar basal ventilation and hypoxic ventilatory response to 10% O 2 , but increased HVR at 6%O 2 (Soliz et al, 2005).…”

“…In our last study we showed that the intracisternal administration of soluble Epo receptor (sEpoR, a competitive antagonist of Epo) in the brainstem of newborn and adult C57/Bl6 mice significantly decreases the minute ventilation and the hypoxic ventilatory response. Accordingly, we concluded that endogenous cerebral Epo is a potent respiratory stimulant (Ballot et al, 2015). Furthermore, recent data obtained on the in vitro preparation of the isolated brainstem spinal cord of newborn mice showed that Epo reduces the classical hypoxic depression of the fictive breathing frequency (Khemiri et al, 2011).…”

“…This equation allows the correction for the changes of gas composition in the inflowing and outflowing gas lines due to the activity of the animal, and the day‐to‐day variability of CO 2 and H 2 O in the air (Lighton and Halsey, 2011). Since in our previous study the most important effect of Epo on hypoxic ventilatory response in newborn mice was assessed by the ratio of minute ventilation () to O 2 consumption () (Ballot et al, 2015), this value was reported in this work.…”

Sex difference in mouse metabolic response to erythropoietin

“…Gender-specific EPO response was previously observed in the ventilatory response in rodents. EPO enhanced the ventilatory response to hypoxia in a sexdependent manner, with female mice coping better with reduced oxygenation while male mice exhibited a larger ventilatory response to intracisternal injections of soluble EpoR (29,(32)(33)(34). The protective effect of EPO against cisplatin-induced nephrotoxicity was stronger in male rats than female rats (35), and the neuroprotective effect of EPO provided after neonatal stroke seemed to be more effective in female rats than male rats (36).…”

Respiratory regulation by steroids in newborn rats: a sex‐specific balance between allopregnanolone and progesterone receptors

“…Oxygen, CO 2 and water pressure levels in the inflow and outflow gas lines were measured with dedicated gas analysers (S3-A/II, CD3A, AEI Technologies; and RH-300, Sable Systems International), allowing the measurement of O 2 consumption (V O 2 ), CO 2 production (V CO 2 ), the O 2 convection ratio (V E /V O 2 ) and the CO 2 convection ratio (V E /V CO 2 ). Details on the formula used for all these calculations are as previously described (Bairam et al 2013;Ballot et al 2015;Uppari et al 2016). All signals were recorded using Spike2 software (Cambridge Electronic Design, Cambridge, UK) and stored on a computer for further analyses.…”