Conditional knockout of activin like kinase-1 (ALK-1) leads to heart failure without maladaptive remodeling

Abstract

Activin like kinase-1 (ALK-1) mediates signaling via the transforming growth factor beta (TGFβ) family of ligands. ALK-1 activity promotes endothelial proliferation and migration. Reduced ALK-1 activity is associated with arteriovenous malformations. No studies have examined the effect of global ALK-1 deletion on indices of cardiac remodeling. We hypothesized that reduced levels of ALK-1 promote maladaptive cardiac remodeling. Methods We studied ALK-1 conditional knockout mice (cKO) harboring the ROSA26-CreER knock-in allele whereby a single dose of intraperitoneal tamoxifen triggered ubiquitous Cre-recombinase mediated excision of floxed ALK-1 alleles. Tamoxifen treated wild-type (WT-TAM; n=5) and vehicle treated ALK-1-cKO mice (cKO-CON; n=5) served as controls for tamoxifen treated ALK-1-cKO mice (cKO-TAM; n=15). Results ALK-1 cKO-TAM mice demonstrated reduced 14-day survival compared to cKO-CON controls (13% vs 100%, respectively, p<0.01). Seven days after treatment, cKO-TAM mice began to exhibit reduced left ventricular (LV) fractional shortening, progressive LV dilation, and gastrointestinal bleeding. After 14 days total body mass was reduced, but LV and lung mass increased in cKO-TAM not cKO-CON mice. Peak LV systolic pressure, contractility, and arterial elastance were reduced, but LV end-diastolic pressure and stroke volume were increased in cKO-TAM, not cKO-CON mice. LV ALK-1 mRNA levels were reduced in cKO-TAM, not cKO-CON mice. LV levels of other TGFβ-family ligands and receptors (ALK5, TBRII, BMPRII, Endoglin, BMP7, BMP9, and TGFβ1) were unchanged between groups. Cardiomyocyte area and LV levels of BNP were increased in cKO-TAM mice, but LV levels of β-MHC and SERCA were unchanged. No increase in markers of cardiac fibrosis, Type I collagen, CTGF, or PAI-1, were observed between groups. No differences were observed for any variable studied between cKO-CON and WT-TAM mice. Conclusion Global deletion of ALK-1 is associated with the development of high output heart failure without maladaptive remodeling. Future studies exploring the functional role of ALK-1 in cardiac remodeling independent of systemic AVMs are required.

Reduced activin receptor-like kinase 1 activity promotes cardiac fibrosis in heart failure

“…No phenotypic affect was observed with cardiomyocyte specific deletion of Alk1 . Recently we demonstrated that global inducible knockout of Alk1 expression in adult mice led to the development of gastrointestinal arteriovenous malformations and high output HF without structural or signaling changes consistent with pathological cardiac remodeling [8, 9]. We have now studied Alk1 haploinsufficient mice and observed no change in cardiac structure or function at baseline compared to WT mice; however cardiac function worsened and cardiac fibrosis increased in Alk1 +/− mice after TAC.…”

“…Recently, several reports have implicated a role for ALK1 as a negative regulator of fibrosis in vascular tissue, cartilage, the liver and the kidney [9, 16–19]. From these observations, we hypothesized that reduced ALK1 activity promotes cardiac fibrosis in HF by limiting SMAD1 activation.…”

“…In mice, homozygous deletion of Alk1 results in embryonic lethality due to severe defects in cardiovascular development [6, 8]. Global inducible knockout of Alk1 in adult mice results in lethality associated with the formation of arteriovenous malformations in the gastrointestinal tract and subsequent development of high output HF[8, 9]. For this reason, several studies have employed the Alk1 heterozygous mouse model to study the post-natal effects of ALK1 deficiency [6, 10, 11].…”

ALK1 signaling in development and disease: new paradigms

“…Tissue-specific deletion demonstrates a requirement for acvrl1 in ECs [56, 57]. Conditional global or endothelial-specific Acvrl1 deletion is also lethal in neonates and adults, with animals exhibiting AVMs and hemorrhage in uterus, lung, gastrointestinal tract, and retina, but not in brain or skin [57–62]. Interestingly, brain and skin AVMs develop in Acvrl1 -deleted mice in response to VEGF stimulation or wounding, suggesting that a “second hit” that triggers angiogenesis is required for AVM development in these tissues [56–59, 63–66].…”

“…Interestingly, brain and skin AVMs develop in Acvrl1 -deleted mice in response to VEGF stimulation or wounding, suggesting that a “second hit” that triggers angiogenesis is required for AVM development in these tissues [56–59, 63–66]. Global deletion in adulthood is also associated with cardiomegaly and high-output heart failure [57, 62] that may be caused, as in HHT patients, by low peripheral vascular resistance. Together, these studies point to a critical requirement for Acvrl1 in vascular development and maintenance throughout life.…”