Gold nanorods modified by endogenous protein with light-irradiation enhance bone repair via multiple osteogenic signal pathways

Abstract

Fracture is one of the most common clinical diseases that reduce the quality of patients’ lives significantly. In this study, we prepared gold nanorods modified by endogenous proteins which collected from the autologous blood of individual mice for enhanced photothermal therapy (PTT) to treat fracture. Due to the outermost layer being endogenous proteins, we find that GNRs neither activate the immune cells in vitro nor cause any rejection immune responses after entering the body as compared with PEG modification. In addition, the internal bleeding and edema of the fracture site result in a rapid enrichment of GNRs after intravenous injection. Under near infrared (NIR) light irradiation, the mild photothermal effect of the accumulated GNRs can effectively promote healing of fracture in mice. The molecular mechanism of osteogenic capability is revealed by transcriptome sequencing and subsequent confirmatory experiments, indicating enhanced two key osteogenic signal transduction (MAPK, PI3K-Akt) and multiple key osteogenesis related factors expression following the treatment. Our strategy offers an alternative way to promote bone regeneration following a fracture.

Introduction

Fracture is a common sequelae of injuries and a major cause of morbidity and mortality, especially if left untreated [[1], [2], [3]]. The traditional treatment is to fix the fracture site of the fractures [4]. However, the fracture healing effect varies from person to person, leading to considerable uncertainty [5,6]. In addition, the management of fractures is complex, with the high risk of mal-union, delayed union and non-union, reducing the quality of patients’ lives [7,8]. Hence, it is crucial to develop innovative therapies for enhanced bone regeneration to overcome these restrictions [9].

Previous bone regeneration studies have indicated that photothermal stress could stimulate bone tissue growth [[10], [11], [12], [13]]. Photothermal therapy (PTT) is emerging as a potential approach for promoting bone formation due to its high selectivity and minimal invasiveness [14,15]. Studies have found that PTT can improve the adhesion, proliferation, differentiation and osteogenic gene expressions of bone mesenchymal stem cells [14,16]. Near infrared (NIR) light (700–1300 nm) has received much attention in the field of PTT, due to its better tissue penetration [17].However, how to improve the PTT efficacy of NIR and promote the regeneration of damaged tissue still needs further exploration.

Photothermal materials can efficiently convert light energy into heat. Among several photothermal materials, gold nanomaterials stand out due to their ease of synthesis, stability, better biocompatibility, and outstanding photothermal effect [18]. Polyethylene glycol (PEG) modification is a general way to improve biocompatibility [19]. However, recent studies have demonstrated the occurrence of anti-PEG antibodies in animal models immunized with PEGylated proteins or PEGylated biopharmaceuticals, which result in somewhat rejection of the body and immune responses [20,21].

In order to overcome the difficulties mentioned above, we modified gold nanorods (GNRs) with endogenous proteins collected from the autologous blood for PTT of fracture. The type and bioactivity of endogenous proteins are individual specific. Therefore, endogenous proteins have extremely low immunogenicity for individuals and can be used as personalized modification strategy. We found that unlike PEG-modified GNRs, endogenous protein-modified GNRs (eP@GNRs) did not elicit immune inflammation and immune rejection neither in vitro nor in vivo. The eP@GNRs that reach the fracture site produce mild photothermal effect under NIR irradiation, thereby promoting bone tissue regeneration. Furthermore, transcriptome sequencing and subsequent confirmatory experiments further reveal the mechanisms of osteogenic capability. Our strategy provides an alternative approach to promote bone regeneration with promising clinical translation prospects.