Activation of Toll-like receptor 7 provides cardioprotection in septic cardiomyopathy-induced systolic dysfunction

BACKGROUND

As a pattern recognition receptor, Toll-like receptor 7 (TLR7) widely presented in the endosomal membrane of various cells. However, the precise role and mechanism of TLR7 in septic cardiomyopathy remain unknown. This study aims to determine the role of TLR7 in cardiac dysfunction during sepsis and explore the mechanism of TLR7 in septic cardiomyopathy.

METHODS

We generated a mouse model of septic cardiomyopathy by challenging with lipopolysaccharide (LPS). TLR7-knockout (TLR7-/- ), wild-type (WT) mice, cardiac-specific TLR7-transgenic (cTG-TLR7) overexpression, and littermates WT (LWT) mice were subjected to septic model. Additionally, to verify the role and mechanism of TLR7 in vitro, we transfected neonatal rat ventricular myocytes (NRVMs) with Ad-TLR7 and TLR7 siRNA before LPS administration. The effects of TLR7 were assessed by Ca2+ imaging, western blotting, immunostaining, and quantitative real-time polymerase chain reaction (qPCR).

RESULTS

We found that TLR7 knockout markedly exacerbated sepsis-induced systolic dysfunction. Moreover, cardiomyocytes isolated from TLR7-/- mice displayed weaker Ca2+ handling than that in WT mice in response to LPS. Conversely, TLR7 overexpression alleviated LPS-induced systolic dysfunction, and loxoribine (TLR7-specific agonist) improved LPS-induced cardiac dysfunction. Mechanistically, these optimized effects were associated with enhanced the adenosine (cAMP)-protein kinase A (PKA) pathway, which upregulated phosphorylate-phospholamban (p-PLN) (Ser16) and promoted sarco/endoplasmic reticulum Ca2+ ATPase (Serca) and Ryanodine Receptor 2 (RyR2) expression in the sarcoplasmic reticulum (SR), and ultimately restored Ca2+ handling in response to sepsis. While improved Ca2+ handling was abrogated after H89 (a specific PKA inhibitor) pretreatment in cardiomyocytes isolated from cTG-TLR7 mice. Consistently, TLR7 overexpression improved LPS-induced Ca2+ -handling decrement in NRVMs. Nevertheless, TLR7 knockdown showed a deteriorative phenotype.

CONCLUSIONS

Our data demonstrated that activation of TLR7 protected against sepsis-induced cardiac dysfunction through promoting cAMP-PKA-PLN pathway, and we revealed that TLR7 might be a novel therapeutic target to block the septic cardiomyopathy and support systolic function during sepsis.

Studies on nerve cell affinity of chitosan-derived materials

Reparation of the central nervous system (CNS) is important because when it is impaired its recovery is difficult and concomitant malfunction of other parts of body occurs. In our previous studies, chitosan was found to be a good material supporting nerve repair. The purpose of this article was to study the ability of chitosan and some chitosan-derived materials to facilitate the growth of nerve cells. Those materials were chitosan, glutaraldehyde-crosslinked chitosan, glutaraldehyde-crosslinked chitosan-gelatin conjugate, a chitosan-gelatin mixture, chitosan coated with polylysine (CAP), and a chitosan-polylysine mixture (CPL). Gelatin and polylysine were used as controls. After nerve cells (gliosarcoma cells and normal cerebral cells) were grown on those materials, their attachment, spread, and growth were observed. The adsorption of some extracellular matrix molecules such as laminin and fibronectin on the materials and the role the molecules play in nerve cell attachment and spreading were also studied by enzyme-linked immunosorbent assay and MTT method. We found that both CAP and CPL have excellent nerve cell affinity, defined as the ability to promote nerve cell to grow and function normally. Those two materials may be promising for the repair of the nervous system. Materials precoated with laminin, fibronectin, and serum were analyzed for their nerve cell affinity. Results suggest that after being precoated with laminin and fibronectin solution or serum, all material have better nerve cell affinity.