Adenosine regulation of microtubule dynamics in cardiac hypertrophy

Abstract

There is evidence that endogenous extracellular adenosine reduces cardiac hypertrophy and heart failure in mice subjected to chronic pressure overload, but the mechanism by which adenosine exerts these protective effects is unknown. Here, we identified a novel role for adenosine in regulation of the cardiac microtubule cytoskeleton that may contribute to its beneficial effects in the overloaded heart. In neonatal cardiomyocytes, phenylephrine promoted hypertrophy and reorganization of the cytoskeleton, which included accumulation of sarcomeric proteins, microtubules, and desmin. Treatment with adenosine or the stable adenosine analog 2-chloroadenosine, which decreased hypertrophy, specifically reduced accumulation of microtubules. In hypertrophied cardiomyocytes, 2-chloroadenosine or adenosine treatment preferentially targeted stabilized microtubules (containing detyrosinated α-tubulin). Consistent with a role for endogenous adenosine in reducing microtubule stability, levels of detyrosinated microtubules were elevated in hearts of CD73 knockout mice (deficient in extracellular adenosine production) compared with wild-type mice (195%, P < 0.05). In response to aortic banding, microtubules increased in hearts of wild-type mice; this increase was exaggerated in CD73 knockout mice, with significantly greater amounts of tubulin partitioning into the cold-stable Triton-insoluble fractions. The levels of this stable cytoskeletal fraction of tubulin correlated strongly with the degree of heart failure. In agreement with a role for microtubule stabilization in promoting cardiac dysfunction, colchicine treatment of aortic-banded mice reduced hypertrophy and improved cardiac function compared with saline-treated controls. These results indicate that microtubules contribute to cardiac dysfunction and identify, for the first time, a role for adenosine in regulating cardiomyocyte microtubule dynamics.

AMPK attenuates microtubule proliferation in cardiac hypertrophy

“…In support of a role for MT accumulation in contractile dysfunction in AMPK KO mice, we observed that polymerized microtubule levels correlated strikingly with reduced left ventricular ejection fraction and pulmonary congestion in mice exposed to TAC. Furthermore, our previous study demonstrated that periodic colchicine treatment attenuated chamber dilation and improved contractile function in Balb-c mice exposed to pressure overload (7). The present data suggest that agents that activate AMPK may similarly preserve contractile function by preventing MT densification.…”

“…Neonatal rat ventricular cardiomyocytes (NRVMs) were isolated from 2-day-old Sprague-Dawley rats by enzymatic digestion and separated from nonmuscle cells on a discontinuous Percoll gradient. NRVMs were isolated from 2-day-old Sprague-Dawley rats by enzymatic digestion and separated from nonmuscle cells on a discontinuous Percoll gradient, as previously described (7). A total of 2-4 million viable myocytes were isolated per ventricle with very little fibroblast contamination (Ͻ2%) and plated on gelatin-coated plates in serum-containing DMEM (0.5-1 ϫ 10 5 cells/cm 2 ) and incubated for 48 h to allow attachment and spreading, after which, the medium was replaced with serum-free media for 24 h prior to treatment.…”

“…Microtubules also play an important role in ion channel trafficking (29), mRNA transport (22,27), and intracellular organization (38,40,43), and disruption of these microtubule functions by aberrant stabilization in pressure overload may also contribute to adverse remodeling and heart failure. In support of a role for MT stabilization in contractile dysfunction, we found that chronic (every other day) treatment with colchicine to reduce MT densification attenuated hypertrophy and improved contractile function in Balb-c mice exposed to pressure overload produced by transverse aortic constriction (TAC) (7). Identification of endogenous pathways that regulate cardiac microtubule dynamics may thus provide pharmacological targets for attenuating microtubule-related ventricular dysfunction in the hypertrophied heart.…”

Cytoskeletal role in protection of the failing heart by β-adrenergic blockade

“…The fact that increased ␤-adrenergic activity is regularly seen in pathological cardiac hypertrophy, including this model of severe RV pressure overloading (14), together with the recent observation that ␤-adrenergic agonists cause Pak1 activation (33), and that adenosine inhibits the cardiac hypertrophy-dependent microtubule changes (19), likely through its antiadrenergic effects (12), led to the present study; that is, in the setting of this knowledge, we hypothesized and then showed here that chronic ␤-adrenergic blockade would prevent the abnormal microtubule network from forming during pathological cardiac hypertrophy.…”

Opposing Actions of Extracellular Signal-regulated Kinase (ERK) and Signal Transducer and Activator of Transcription 3 (STAT3) in Regulating Microtubule Stabilization during Cardiac Hypertrophy

“…As MT reorganization is specifically linked to cardiac hypertrophy associated with contractile dysfunction (13, 37), our findings suggest that stable MTs could be promoted in the absence or down-regulation of ERK activity and is consistent with ERK function in promoting cardiac hypertrophy without contractile deficits. One complication arises with the recent study reporting modest elevation of glu-tubulin levels in PEtreated neonatal cardiac myocytes, although this study did not investigate effects of other hypertrophic stimuli such as the IL6 family of cytokines or the specific role for the ERK MAPKs (35).…”