In 2020, UNICEF and WHO approximated 15% of babies born annually are considered small for gestational age and roughly 23% of children up to the age of 5 suffer from early life growth restriction worldwide. Alarmingly, early life growth restriction is linked with chronic disease development in adulthood. The NNERL has established PNGR causes smaller and less binucleated cardiomyocytes, disrupted collagen proteins, impaired Ca2+ signaling, widened QRS complexes and elongated isovolumic relaxation time, all suggestive of cardiac dysfunction that disproportionately affects females. The increased severity in females suggests a possible sex steroid phenomenon, as sex steroids present one of the largest biological differences between males and females. Therefore, the purpose of this dissertation was to determine the influence of postnatal growth restriction on cardiovascular development with a focus on sex steroids, in a mouse model. Study one hypothesized PNGR would increase testosterone but decrease estradiol in adulthood; study two hypothesized PNGR would reduce Ca2+ regulating protein abundance disrupting Ca2+ kinetics and reducing cardiac function; and finally study three hypothesized that PNGR female mice have increased collagen deposition leading to cardiac fibrosis and stiffness of the heart.All three studies were conducted with a validated nutritive cross-fostering model to isolate growth restriction to the postnatal period. In brief, mouse dams were placed on either a normal protein diet (20%) or a low protein diet (8%) two weeks prior to mating. The dams on the low protein diet produce ~20% less milk which reduces overall nutrient intake and stunts organ growth in the offspring. On postnatal day (PN) 1 cross-fostering was accomplished by placing normal protein born pups with a low protein fed dam or a different normal protein fed dam (CON). On PN 21, all mice were weaned and placed on the same 20% normal protein diet into adulthood. In study one blood samples were collected from female mice at two time points PN 70 and 130. Serum was then separated from plasma and steroid levels were assessed with mass spectrometry. Testosterone levels were not different between PNGR and CON mice at either timepoint, while estradiol was only detected in 25% of PNGR and 66% of CON. However, a precursor steroid, 18-hydroxycortisol, was elevated in PNGR female mice and suggests the PNGR mice suffer from hypertension. For study two, cardiac samples were collected at PN 21, 70, and 130 to assess Ca2+ handling protein abundance. Serca2 was reduced in PNGR female mice indicating a disruption in Ca2+ reuptake. However, there were no differences between CON and PNGR for the regulators of Serca2 [phospholamban (PLN), phosphorylated PLN (P-PLN), protein kinase A (PKA) and phosphorylated PKA (P-PKA)]. Finally, in study three the female mice were euthanized at PN 21, 70, and 130 and hearts were excised for protein quantification of endothelin-1 (ET-1) and a second heart was collected at PN 130 for histology staining of collagen. ET-1 is a potent stimulator protein of cardiac remodeling and fibrosis while Masson’s Trichrome stain detects collagen fibers. At PN 21, 70, and 130, ET-1 protein in the heart was not different between CON and PNGR female mice and at PN 130 the PNGR mice did not have more collagen in the myocardium than CON mice. Together, the three studies of this dissertation filled a gap in the literature and confirm impaired relaxation in the PNGR female hearts is linked to changes in Ca2+ modulation via a reduction in Serca2 but without cardiac fibrosis. Despite not being able to determine estradiol levels in 75% of PNGR samples from study one, the elevated 18-hydroxycortisol in PNGR females suggest hypertension may be increasing their risk of CVD. Future research is recommended to focus on increasing Serca2 regulated Ca2+ reuptake and reducing hypertension to mitigate impaired relaxation in the PNGR females.
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