Angiotensin II stimulates hyperplasia but not hypertrophy in immature ovine cardiomyocytes

Abstract

Rat and sheep cardiac myocytes become binucleate as they complete the 'terminal differentiation' process soon after birth and are not able to divide thereafter. Angiotensin II (Ang II) is known to stimulate hypertrophic changes in rodent cardiomyocytes under both in vivo and in vitro conditions via the AT1 receptor and intracellular extracellular regulated kinase (ERK) signalling cascade. We sought to develop culture methods for immature sheep cardiomyocytes in order to test the hypothesis that Ang II is a hypertrophic agent in the immature myocardium of the sheep. We isolated fetal sheep cardiomyocytes and cultured them for 96 h, added Ang II and phenylephrine (PE) for 48 h, and measured footprint area and proliferation (5-bromo-2'-deoxyuridine (BrdU) uptake) separately in mono- vs. binucleate myocytes. We found that neither Ang II nor PE changed the footprint area of mononucleated cells. PE stimulated an increase in footprint area of binucleate cells but Ang II did not. Ang II increased myocyte BrdU uptake compared to serum free conditions, but PE did not affect BrdU uptake. The MAP kinase kinase (MEK) inhibitor UO126 prevented BrdU uptake in Ang II-stimulated cells and prevented cell hypertrophy in PE-stimulated cells. This paper establishes culture methods for immature sheep cardiomyocytes and reports that: (1) Ang II is not a hypertrophic agent; (2) Ang II stimulates hyperplastic growth among mononucleate myocytes; (3) PE is a hypertrophic agent in binucleate myocytes; and (4) the ERK cascade is required for the proliferation effect of Ang II and the hypertrophic effect of PE.

Prenatal Exposure to Dexamethasone in the Mouse Alters Cardiac Growth Patterns and Increases Pulse Pressure in Aged Male Offspring

“…The AT 1a R receptor is the predominant angiotensin II receptor subtype in the heart [46] and it plays a key role in mediating the myocardial trophic effects of angiotensin II [47], [48] stimulating both hypertrophy and/or hyperplasia. IGF-1 plays a major role in cardiac growth, stimulating cardiomyocyte hypertrophy and hyperplasia.…”

“…IGF-1 plays a major role in cardiac growth, stimulating cardiomyocyte hypertrophy and hyperplasia. The immature mouse cardiomyocytes are capable of both proliferation and hypertrophy at E17.5 [48], [49]. Hence, it is likely that the increase in AT 1a R and IGF-1 mRNA levels in DEX exposed fetuses at E17.5 may be driving the increase in heart weight from its relatively small size at E14.5 back to normal by E17.5.…”

The effect of adrenalectomy on the cardiac response to subacute fetal anemia

“…Sundgren and colleagues found that activation of ERK and PI3K by IGF-1, and ERK alone by angiotensin II, stimulates fetal sheep cardiomyocyte proliferation in vitro (Sundgren 2003a; Sundgren 2003b). The ERK cascade was also required for the in vitro hypertrophic effects of phenylephrine.…”

Endocrine and other physiologic modulators of perinatal cardiomyocyte endowment

“…AII causes near-term fetal sheep cardiomyocytes to proliferate in culture, contrary to its hypertrophic effect in cultured neonatal rat cardiomyocytes (O’Tierney et al 2010; Sundgren et al 2003). In contrast, AII infusion in utero increases ovine heart growth via myocyte hypertrophy and maturation (Norris et al 2014; Sandgren et al 2015; Segar et al 2001).…”

“…For instance, AII-induced fetal cardiac growth is dependent on its hypertensive effect (Sandgren et al 2015), despite causing fetal sheep cardiomyocyte proliferation in culture (Sundgren et al 2003). Similarly, the effects of cortisol depend on site of administration and fetal hemodynamic effects (Giraud et al 2006; Lumbers et al 2005; Reini et al 2008).…”