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  • To promote biomimetic growth of HAp Li et

    2022-06-23

    To promote biomimetic growth of HAp, Li et al. [20] developed a technique to modify cellulose nanofibers using P2O5. It was ascertained that the negative phosphate groups bonded with Ca2+ through coordination bonds and subsequently guided the growth of the Ca–P crystals throughout the scaffolds. Similarly, phosphorylation of chitosan with P2O5 was also utilized to synthesize a complex composite of HAp and phosphorylated chitosan for bone regeneration [21]. As a type of transferase, kinases exhibit the capability to catalyze the phosphorylation of specific substrates in the presence of phosphate-donating molecules such as ATP [22]. As an energy supplier, ATP consists of the high-energy phosphate groups and is involved the metabolic process in vivo of sugar, fat, nucleic Cholera Toxin mg and protein. Therefore, the enzymatic phosphorylation of SF can be considered an eco-friendly alternative for the synthesis of biocomposites for bone tissue engineering. To develop this novel method, we attempted to prepare a phosphorylated fibroin using a two-step process with laccase (EC 1.10.3.2) and hexokinase (EC 2.7.1.1) so as to bring about more efficient HAp crystal growth onto the SF matrices during mineralization. Firstly, as depicted in Fig. 1(a), laccase-catalyzed grafting of chitooligosaccharide (COS) onto SF was achieved via a Schiff base reaction between the tyrosine residues and the amino groups in COS, in an attempt to improve the formability and antibacterial properties of SF [23]. Subsequently, enzymatic phosphorylation of COS-grafted SF was initiated using a combination of hexokinase and Mg-chelated ATP. Hexokinase is an enzyme that phosphorylates the six-carbon rings in carbohydrates such as glucose on their phosphates [24,25] and has the potential to convert COS to aminoglucose-6-phosphate (Fig. 1(b)). It was hypothesized that this combined method might promote the adsorption of calcium ions onto the fibroin chains, which would encourage deposition of calcium phosphate during biomimetic mineralization.
    Experimental
    Results and discussion
    Conclusions The following are the supplementary data related to this article.
    Acknowledgments This work was financially supported by the National Natural Science Foundation of China (31771039, 51373071), the Fundamental Research Funds for the Central Universities (JUSRP51717A), the 111 Project (B17021) and Qing Lan Project of Jiangsu Province (SJ2016-15).
    Introduction The brain has high energy requirements due to excitatory neurotransmission and the high ATP turnover sets the brain at a stage susceptible to ischemic injury. In response to nutrient depletion, glutamate release-mediated excitotoxicity is the main cause of cerebral ischemic damage [1]. Glutamate is the main excitatory neurotransmitter in central nervous system and required for neuronal growth, maturation and synaptic plasticity [2]. However, an excessive release of glutamate can trigger neuronal death during brain ischemia. Glutamate-induced neuronal death is usually through the activation of N-methyl-D-aspartate (NMDA) Cholera Toxin mg receptor, especially extrasynaptic NMDA receptors. Although different signaling cascades and multiple ways of cell death are involved in glutamate-induced neuronal damage, mitochondrial dysfunction emerges as a key event linking altered metabolism with subsequent neuronal death [3]. In line with this, impaired ion homeostasis, oxidative stress, inflammation and endoplasmic reticulum stress are tightly associated with mitochondrial malfunction, contributing to neuronal death in mitochondrial way [4], [5]. Therefore, the stability of mitochondrial structure and function is essential for neuronal survival during ischemic injury. Mitochondrial homeostasis is maintained by the permeability barrier of the inner mitochondrial membrane (IMM), and the binding of hexokinase-II (HK-II) to mitochondria is demonstrated to protect mitochondrial function from ischemic injury by preventing the opening of the mitochondrial permeability transition pore (mPTP) [6]. Hexokinase (HK) is the key enzyme catalyzing the first step of glycolysis. In mammals, there are four known distinct isoforms of hexokinases, nevertheless only the isoforms of HK-I and HK-II possess the N-terminal hydrophobic segment which binds to mitochondria [7], [8]. HK-I is the predominant isoform in brain, but only HK-II owns the capacity of regulating mitochondrial homeostasis [8]. The combination of HK-II with mitochondria is not static and HK-II translocates between mitochondria and cytoplasm in response to cellular stresses. Under physiological conditions, the association of HK-II with mitochondrial voltage-dependent anion channel (VDAC) in mitochondrial outer membrane enhances the efficiency of glycolysis and oxidative metabolism [9]. Moreover, VDAC-bound HK-II prevents the opening of mPTP by means of competitive inhibition of bax/bak binding to VDAC [9], [10], [11]. Upon ischemic insult, altered redox state, oxidative stress and intracellular acidification impair mitochondrial HK-II and the detachment of HK-II from VDAC results in the opening of mPTP [12], [13]. The subsequent mitochondrial depolarization and the release of pro-apoptotic proteins are the main causes for apoptosis during ischemic injury. In contrast, pharmacological intervention to preserve mitochondrial HK-II is shown to protect mitochondrial function and reduce apoptosis in ischemic heart and brain [14], [15].