GDF11 does not rescue aging-related pathological hypertrophy

Abstract

Rationale: Growth differentiation factor 11 (GDF11) is a member of the transforming growth factor-β super family of secreted factors. A recent study showed that reduced GDF11 blood levels with aging was associated with pathological cardiac hypertrophy (PCH) and restoring GDF11 to normal levels in old mice rescued PCH.

Objective: To determine whether and by what mechanism GDF11 rescues aging dependent PCH.

Methods and results: Twenty-four-month-old C57BL/6 mice were given a daily injection of either recombinant (r) GDF11 at 0.1 mg/kg or vehicle for 28 days. rGDF11 bioactivity was confirmed in vitro. After treatment, rGDF11 levels were significantly increased, but there was no significant effect on either heart weight or body weight. Heart weight/body weight ratios of old mice were not different from 8- or 12-week-old animals, and the PCH marker atrial natriuretic peptide was not different in young versus old mice. Ejection fraction, internal ventricular dimension, and septal wall thickness were not significantly different between rGDF11 and vehicle-treated animals at baseline and remained unchanged at 1, 2, and 4 weeks of treatment. There was no difference in myocyte cross-sectional area rGDF11 versus vehicle-treated old animals. In vitro studies using phenylephrine-treated neonatal rat ventricular myocytes, to explore the putative antihypertrophic effects of GDF11, showed that GDF11 did not reduce neonatal rat ventricular myocytes hypertrophy, but instead induced hypertrophy.

Conclusions: Our studies show that there is no age-related PCH in disease-free 24-month-old C57BL/6 mice and that restoring GDF11 in old mice has no effect on cardiac structure or function.

Keywords: aging; body weight; cardiac function tests; growth differentiation factors; transforming growth factor beta.

Figure 1. Assessment of hypertrophy in vivo

A: Heart weight, body weight, and tibia length was measured at time of sacrifice 28 days post initial injection of GDF11. No significant differences were found between GDF11 and vehicle treated animals. *=p≤0.05 compared to 8 week old mice. B: There was no difference in myocyte cross sectional area between rGDF11 and vehicle treated animals. 100–175 myocytes with nuclei from 6 animals were analyzed per group Scale bar= 50 microns. C: There was no difference in ANP levels between young and aged mice. There was no significant difference between GDF11 and vehicle treated animals. *p<0.05 vs 8 week old mice. #p<0.05 vs 12 week old mice.

Figure 2. Cardiac structure and function measured by echocardiography

Mice received echocardiography at baseline, 1, 2, and 4 weeks after the start of injections. rGDF11 did not affect any A: structural or B: functional parameters measured. rGDF11 (n=21) or vehicle (n=22)

Figure 3. Intra-left ventricular pressures

In vivo intra-LV pressures were measured at time of sacrifice. There was no difference in max pressure, max dP/dT, min dP/dt, EDP, or Tau between rGDF11 (n=21) and vehicle (n=22) treated animals.

Figure 4. GDF11 induces hypertrophy in NRVMs

A: 150–300 myocytes were analyzed from at least 20 fields of view per condition B–C: GDF11 treatment increased expression of ANP and BNP mRNA expression (n=3) *p<0.05 vs control. #p<0.05 vs PE 50μM.