Alexander Pendleton's Abstracts

Alexander Pendleton

Ph.D. Candidate

Physiological Sciences

 

 

Perinatal Exposures: Intersecting Mechanisms leading to Developmental Outcomes

Aspen Snowmass, CO 

August 24-27, 2019

 

Placental insufficiency-induced intrauterine growth restriction (IUGR) fetuses have reduced muscle mass and lower hind-limb protein accretion rates. Weight-specific oxygen uptake was lower in IUGR fetal hind-limb, indicating that muscle growth and metabolism are conserved due decreased mitochondrial function. Our objective was to evaluate mitochondrial oxygen consumption rate (OCR), and Complex 1 activity and expression to determine whether skeletal muscle mitochondrial function is lower in IUGR fetuses.


Ewes were randomly assigned to either a control (CON; n=5) or IUGR (n=4) groups. IUGR fetuses were created by exposing pregnant ewes to elevated ambient temperatures (40º C for 12 h; 35º C for 12 h) in mid-gestation. At gestation day133±1, fetuses were necropsied and biceps femoris muscle was collected for mitochondrial isolation. State 2 (+ 150mM ADP/no substrates) and State 3 (+150mM ADP/+5mM substrates) OCRs were determined using respiratory substrates (glutamate/malate, +/- ADP) or inhibitors in a NeoFox system. Complex 1 activity was measured with a colorimetric assay, and NDUFB8 (Complex 1) expression was determined via immunoblot. Measurements were analyzed by ANOVA and LSD test.


There were no significant differences in State 2 respiration rates between IUGR or CON mitochondria (0.67±0.07 vs 0.99±0.23 nmol O2/min/mg); however, IUGR mitochondria had lower (P<0.05) State 3 respiration rates relative to CON (5.4±1.2 vs 12.0±1.5 nmol O2/min/mg). There were no differences in mitochondrial OCRs between groups upon the addition of Oligomycin A, Rotenone, or cytochrome C. Complex 1 activity was lower (P<0.01) in PI-IUGR muscle relative to CON (26±1.8 vs 31±3.6 mOD/min/mg). NDUFB8 expression was lower in PI-IUGR (P<0.05) compared to CON.


State 3 mitochondrial OCRs were depressed in IUGR fetal skeletal muscle due to decreased Complex 1 activity. Lower Complex 1 activity may decrease oxidative phosphorylation in IUGR skeletal muscle, thus stifling hind-limb growth. This adaptation may be advantageous to IUGR fetuses as it may lower metabolic homeostasis conserving energy for vital tissues.
Supported by NIH RO1 DK084842 and T32 HL007249

 

Abstract for Lay Audience

Placental insufficiency-induced intrauterine growth restriction (IUGR) fetuses have reduced muscle mass as well as a reduced ability to produce muscle. Furthermore, these fetuses have reduced blood oxygen content and reduced blood glucose concentrations. Within all tissues of the body, small organelles called mitochondria use oxygen and glucose to produce energy via a mechanism called the “electron transport chain”. Since IUGR fetuses are impacted by both low oxygen and low glucose, this leads us to believe that IUGR muscle growth and metabolism may be a byproduct of reduced mitochondrial function. Our objective was to evaluate mitochondrial oxygen consumption rate (OCR), and electron transport chain activity (measured by a set of proteins called Complex 1) and expression (measured by a protein called NDUFB8) to determine whether skeletal muscle mitochondrial function is lower in IUGR fetuses.


Ewes were randomly assigned to either a control (CON; n=5) or IUGR (n=4) groups. IUGR fetuses were created by exposing pregnant ewes to elevated ambient temperatures (40º C for 12 h; 35º C for 12 h) in mid-gestation. Our sheep model of IUGR successfully recapitulates the negative outcomes and conditions associated with the human condition of IUGR. Several weeks before term, fetuses were necropsied, and skeletal muscle was collected to isolate mitochondria from the tissue. OCRs were determined using respiratory substrates and electron transport chain activity and expression was determined.


IUGR mitochondria had lower (P<0.05) OCR relative to CON (5.4±1.2 vs 12.0±1.5 nmol O2/min/mg). Furthermore, electron transport chain activity (Complex 1) was lower (P<0.01) in IUGR muscle relative to CON (26±1.8 vs 31±3.6 mOD/min/mg). Also, the expression of the electron transport chain (NDUFB8) was lower in PI-IUGR (P<0.05) compared to CON.


OCRs were depressed in IUGR fetal skeletal muscle due to decreased electron transport chain activity measured by Complex 1. Lower Complex 1 activity may decrease energy production in IUGR skeletal muscle, thus stifling hind-limb growth. This adaptation may be advantageous to IUGR fetuses as it may lower metabolic rates thereby conserving energy for vital tissues.

Last updated 14 Jan 2020