Temporal changes in integrin-mediated cardiomyocyte adhesion secondary to chronic cardiac volume overload in rats

Epigenetic modulation of tenascin C in the heart: implications on myocardial ischemia, hypertrophy and metabolism

BACKGROUND

Tenascin C (TN-C) is considered to play a pathophysiological role in maladaptive left ventricular remodeling. Yet, the mechanism underlying TN-C-dependent cardiac dysfunction remains elusive.

METHOD

The present study was designed to investigate the effect of hypoxia and hypertrophic stimuli on TN-C expression in H9c2 cells and its putative regulation by epigenetic mechanisms, namely DNA promoter methylation and microRNAs. In addition, rats subjected to myocardial infarction (MI) were investigated. H9c2 cells were subjected to oxygen and glucose deprivation; incubated with angiotensin II (Ang II); or human TN-C (hTN-C) purified protein. Hypertrophic and fibrotic markers, TN-C promoter methylation as well as mir-335 expression were assessed by reverse transcription and quantitative polymerase chain reaction while TN-C protein levels were assessed by ELISA.

RESULTS

Tn-C mRNA expression was markedly increased by both oxygen and glucose deprivation and Ang II (P < 0.01, respectively). In addition, Ang-II-dependent TN-C upregulation was explained by reduced promoter methylation (P < 0.05). Cells treated with hTN-C displayed upregulation of Bnp, Mmp2, β-Mhc, integrin α6 and integrin β1. Furthermore, hTN-C treated cells showed a significant reduction in adenosine monophosphate and adenosine triphosphate levels. In vivo, plasma and myocardial TN-C levels were increased 7 days post MI (P < 0.05, respectively). This increment in TN-C was accompanied by upregulation of mir-335 (P < 0.01). In conclusion, both hypoxic and hypertrophic stimuli lead to epigenetically driven TN-C upregulation and subsequent impairment of cellular energy metabolism in cardiomyoblasts.

CONCLUSION

These findings might enlighten our understanding on maladaptive left ventricular remodeling and direct towards a strong involvement of TN-C.

Characterization of adhesion properties of the cardiomyocyte integrins and extracellular matrix proteins using atomic force microscopy

Integrins are transmembrane adhesion receptors that play important roles in the cardiovascular system by interacting with the extracellular matrix (ECM). However, direct quantitative measurements of the adhesion properties of the integrins on cardiomyocyte (CM) and their ECM ligands are lacking. In this study, we used atomic force microscopy (AFM) to quantify the adhesion force (peak force and mean force) and binding probability between CM integrins and three main heart tissue ECM proteins, ie, collagen (CN), fibronectin (FN), and laminin (LN). Functionalizing the AFM probes with ECM proteins, we found that the peak force (mean force) was 61.69 ± 5.5 pN (76.54 ± 4.0 pN), 39.26 ± 4.4 pN (59.84 ± 3.6 pN), and 108.31 ± 4.2 pN (129.63 ± 6.0 pN), respectively, for the bond of CN-integrin, FN-integrin, and LN-integrin. The binding specificity between CM integrins and ECM proteins was verified by using monoclonal antibodies, where α₁₀ - and α₁₁ -integrin bind to CN, α₃ - and α₅ -integrin bind to FN, and α₃ - and α₇ -integrin bind to LN. Furthermore, adhesion properties of CM integrins under physiologically high concentrations of extracellular Ca²⁺ and Mg²⁺ were tested. Additional Ca²⁺ reduced the adhesion mean force to 68.81 ± 4.0 pN, 49.84 ± 3.3 pN, and 119.21 ± 5.8 pN and binding probability to 0.31, 0.34, 0.40 for CN, FN, and LN, respectively, whereas Mg²⁺ caused very minor changes to adhesion properties of CM integrins. Thus, adhesion properties between adult murine CM integrins and its main ECM proteins were characterized, paving the way for an improved understanding of CM mechanobiology.

Cellular Mechanotransduction: From Tension to Function

Living cells are constantly exposed to mechanical stimuli arising from the surrounding extracellular matrix (ECM) or from neighboring cells. The intracellular molecular processes through which such physical cues are transformed into a biological response are collectively dubbed as mechanotransduction and are of fundamental importance to help the cell timely adapt to the continuous dynamic modifications of the microenvironment. Local changes in ECM composition and mechanics are driven by a feed forward interplay between the cell and the matrix itself, with the first depositing ECM proteins that in turn will impact on the surrounding cells. As such, these changes occur regularly during tissue development and are a hallmark of the pathologies of aging. Only lately, though, the importance of mechanical cues in controlling cell function (e.g., proliferation, differentiation, migration) has been acknowledged. Here we provide a critical review of the recent insights into the molecular basis of cellular mechanotransduction, by analyzing how mechanical stimuli get transformed into a given biological response through the activation of a peculiar genetic program. Specifically, by recapitulating the processes involved in the interpretation of ECM remodeling by Focal Adhesions at cell-matrix interphase, we revise the role of cytoskeleton tension as the second messenger of the mechanotransduction process and the action of mechano-responsive shuttling proteins converging on stage and cell-specific transcription factors. Finally, we give few paradigmatic examples highlighting the emerging role of malfunctions in cell mechanosensing apparatus in the onset and progression of pathologies.

Differential Effects of Prevention and Reversal Treatment with Lisinopril on Left Ventricular Remodelling in a Rat Model of Heart Failure

BACKGROUND

Angiotensin converting enzyme (ACE) inhibitors such as lisinopril, represent the front line pharmacological treatment for heart failure, which is characterised by marked left ventricular (LV) dilatation and hypertrophy. This study sought to determine whether initiating treatment with ACE inhibitors at different stages in the remodelling process would alter the efficacy of treatment.

METHODS

To this end, LV size and function were determined in the aortocaval (AV) fistula model of volume overload-induced heart failure. Sprague-Dawley rats were assigned to sham, untreated AV fistula (21 weeks), AV fistula treated with lisinopril (21 weeks), or AV fistula treated with lisinopril from six to 21 weeks post-fistula groups.

RESULTS

Administration of lisinopril for the entire 21-week period prevented LV dilatation, attenuated myocardial hypertrophy and prevented changes in myocardial compliance and contractility, whereas delaying initiation of treatment until six weeks post-fistula attenuated LV dilatation and hypertrophy, however, the delayed onset of treatment had no beneficial effect on ventricular compliance or systolic function.

CONCLUSIONS

The results demonstrate differential effects that can occur with ACE inhibitors depending on the stage during the remodelling process at which treatment is administered.

Non-human primate and rat cardiac fibroblasts show similar extracellular matrix-related and cellular adhesion gene responses to substance P

BACKGROUND

The sensory nerve neuropeptide substance P (SP) regulates cardiac fibrosis in rodents under pressure overload conditions. Interestingly, SP induces transient increased expression of specific genes in isolated rat cardiac fibroblasts, without resultant changes in cell function. This suggests that SP 'primes' fibroblasts, but does not directly activate them. We investigated whether these unusual findings are specific to rodent fibroblasts or are translatable to a larger animal model more closely related to humans.

METHODS

We compared the effects of SP on genes associated with extracellular matrix (ECM) regulation, cell-cell adhesion, cell-matrix adhesion and ECM in cardiac fibroblasts isolated from a non-human primate and Sprague-Dawley rats.

RESULTS

We found that rodent and non-human primate cardiac fibroblasts showed similar responses in genes that relate to ECM regulation and cell adhesion in response to SP. There were large discrepancies in ECM component genes, however, this did not result in collagen or laminin synthesis in rat or non-human primate fibroblasts in response to SP.

CONCLUSIONS

This study further supports the notion that SP serves as a 'primer' for fibroblasts rather than initiating direct effects and suggests that rodent fibroblasts are a suitable model for studying gene and functional responses to SP in the absence of human or non-human primate fibroblasts.