Autophagy and Hsp70 activation alleviate oral epithelial cell death induced by food-derived hypertonicity

Autophagy, a double-edged sword for oral tissue regeneration

BACKGROUND

Oral health is of fundamental importance to maintain systemic health in humans. Stem cell-based oral tissue regeneration is a promising strategy to achieve the recovery of impaired oral tissue. As a highly conserved process of lysosomal degradation, autophagy induction regulates stem cell function physiologically and pathologically. Autophagy activation can serve as a cytoprotective mechanism in stressful environments, while insufficient or over-activation may also lead to cell function dysregulation and cell death.

AIM OF REVIEW

This review focuses on the effects of autophagy on stem cell function and oral tissue regeneration, with particular emphasis on diverse roles of autophagy in different oral tissues, including periodontal tissue, bone tissue, dentin pulp tissue, oral mucosa, salivary gland, maxillofacial muscle, temporomandibular joint, etc. Additionally, this review introduces the molecular mechanisms involved in autophagy during the regeneration of different parts of oral tissue, and how autophagy can be regulated by small molecule drugs, biomaterials, exosomes/RNAs or other specific treatments. Finally, this review discusses new perspectives for autophagy manipulation and oral tissue regeneration.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Overall, this review emphasizes the contribution of autophagy to oral tissue regeneration and highlights the possible approaches for regulating autophagy to promote the regeneration of human oral tissue.

Handelin alleviates cachexia- and aging-induced skeletal muscle atrophy by improving protein homeostasis and inhibiting inflammation

BACKGROUND

Handelin is a bioactive compound from Chrysanthemum indicum L. that improves motor function and muscle integrity during aging in Caenorhabditis elegans. This study aimed to further evaluate the protective effects and molecular mechanisms of handelin in a mouse muscle atrophy model induced by cachexia and aging.

METHODS

A tumour necrosis factor (TNF)-α-induced atrophy model was used to examine handelin activity in cultured C2C12 myotubes in vitro. Lipopolysaccharide (LPS)-treated 8-week-old model mice and 23-month-old (aged) mice were used to examine the therapeutic effects of handelin on cachexia- and aging-induced muscle atrophy, respectively, in vivo. Protein and mRNA expressions were analysed by Western blotting, ELISA and quantitative PCR, respectively. Skeletal muscle mass was measured by histological analysis.

RESULTS

Handelin treatment resulted in an upregulation of protein levels of early (MyoD and myogenin) and late (myosin heavy chain, MyHC) differentiation markers in C2C12 myotubes (P < 0.05), and enhanced mitochondrial respiratory (P < 0.05). In TNF-α-induced myotube atrophy model, handelin maintained MyHC protein levels, increased insulin-like growth factor (Igf1) mRNA expression and phosphorylated protein kinase B protein levels (P < 0.05). Handelin also reduced atrogin-1 expression, inhibited nuclear factor-κB activation and reduced mRNA levels of interleukin (Il)6, Il1b and chemokine ligand 1 (Cxcl1) (P < 0.05). In LPS-treated mice, handelin increased body weight (P < 0.05), the weight (P < 0.01) and cross-sectional area (CSA) of the soleus muscle (P < 0.0001) and improved motor function (P < 0.05). In aged mice, handelin slightly increased the weight of the tibialis anterior muscle (P = 0.06) and CSA of the tibialis anterior and gastrocnemius muscles (P < 0.0001). In the tibialis anterior muscle of aged mice, handelin upregulated mRNA levels of Igf1 (P < 0.01), anti-inflammatory cytokine Il10 (P < 0.01), mitochondrial biogenesis genes (P < 0.05) and antioxidant-related enzymes (P < 0.05) and strengthened Sod and Cat enzyme activity (P < 0.05). Handelin also reduced lipid peroxidation and protein carbonylation, downregulated mRNA levels of Fbxo32, Mstn, Cxcl1, Il1b and Tnf (P < 0.05), and decreased IL-1β levels in serum (P < 0.05). Knockdown of Hsp70 or using an Hsp70 inhibitor abolished the ameliorating effects of handelin on myotube atrophy.

CONCLUSIONS

Handelin ameliorated cachexia- and aging-induced skeletal muscle atrophy in vitro and in vivo, by maintaining homeostasis of protein synthesis and degradation, possibly by inhibiting inflammation. Handelin is a potentially promising drug candidate for the treatment of muscle wasting.

Caenorhabditis elegans LIN-24, a homolog of bacterial pore-forming toxin, protects the host from microbial infection

Aerolysin-like pore-forming protein (af-PFP) superfamily members are double-edge swords that assist the bacterial infection but shied bacteria from the host by various mechanisms in some species including the toad Bombina maxima and zebrafish. While members of this family are widely expressed in all kingdoms, especially non-bacteria species, it remains unclear whether their anti-bacterial function is conserved. LIN-24 is an af-PFP that is constitutively expressed throughout the Caenorhabditis elegans lifespan. Here, we observed that LIN-24 knockdown reduced the maximum lifespan of worms. RNA-seq analysis identified 323 differentially expressed genes (DEGs) post-LIN-24 knockdown that were enriched in "immune response" and "lysosome pathway," suggesting a possible role for LIN-24 in resisting microbial infection. In line with this, we found that Pseudomonas aeruginosa 14 (PA14) infection induced LIN-24 expression, and that survival after PA14 infection was significantly reduced by LIN-24 knockdown. In contrast, LIN-24 overexpression (LIN-24-OE) conferred protection against PA14 infection, with worms showing longer survival time and reduced bacterial load. Weighted gene co-expression network analysis of LIN-24-OE worms showed that the highest correlation module was enriched in factors related to immunity and the defense response. Finally, by predicting transcription factors from RNA-seq data and knocking down candidate transcription factors in LIN-24-OE worms, we revealed that LIN-24 may protect worms against bacterial infection by stimulating DAF-16-mediated immune responses. These findings agree with our previous studies showing an anti-microbial role for the amphibian-derived af-PFP complex βγ-CAT, suggesting that af-PFPs may play a conserved role in combatting microbial infections. Further research is needed to determine the roles this protein family plays in other physio-pathological processes, such as metabolism, longevity, and aging.

Handelin protects human skin keratinocytes against ultraviolet B-induced photodamage via autophagy activation by regulating the AMPK-mTOR signaling pathway

Handelin is a natural ingredient extracted from Chrysanthemum boreale flowers that has been shown to decrease stress-related cell death, prolong lifespan, and promote anti-photoaging. However, whether handelin inhibits ultraviolet (UV) B stress-induced photodamage remains unclear. In the present study, we investigate whether handelin has protective properties on skin keratinocytes under UVB irradiation. Human immortalized keratinocytes (HaCaT keratinocytes) were pretreated with handelin for 12 h before UVB irradiation. The results indicated that handelin protects keratinocytes against UVB-induced photodamage by activating autophagy. However, the photoprotective effect of handelin was suppressed by an autophagic inhibitor (wortmannin) or the transfection of keratinocytes with a small interfering RNA targeting ATG5. Notably, handelin reduced mammalian target of rapamycin (mTOR) activity in UVB-irradiated cells in a manner similar to that shown by the mTOR inhibitor rapamycin. Adenosine monophosphate-activated protein kinase (AMPK) activity was also induced by handelin in UVB-damaged keratinocytes. Finally, certain effects of handelin, including autophagy induction, mTOR activity inhibition, AMPK activation, and reduction of cytotoxicity, were suppressed by an AMPK inhibitor (compound C). Our data suggest that handelin effectively prevents photodamage by protecting skin keratinocytes against UVB-induced cytotoxicity via the regulation of AMPK/mTOR-mediated autophagy. These findings provide novel insights that can aid the development of therapeutic agents against UVB-induced keratinocyte photodamage.

Platycodin D Alleviates High-Glucose-Aggravated Inflammatory Responses in Oral Mucosal Cells by PI3K/mTOR Pathway

Oral mucosal diseases account for an increasing proportion of hμMan diseases. Among the many common risk factors that cause oral diseases and systemic diseases, dietary factors, especially high sugar, are particularly prominent. Exhibiting therapeutic potential in treating certain inflammation-related diseases, platycodin D (PD) has been known to possess anti-inflammatory benefits in cases of cytokine-induced inflammation, a fact that has been widely docμMented. However, there are few studies about PD in the oral mucosal disease. Investigating the effect of PD on high-glucose (HG)-induced inflammatory responses in oral mucosal cells was the endeavor of this study. The results revealed that HG induced cell mortality, promoted activity of inflammatory factor (TNF-α, IL-1β, IL-6, and IL-8), and increased ROS production in oral mucosal cells. Interestingly, PD obviously alleviated HG-induced oral mucosal cells inflammatory response. Simultaneously, the expressions of PI3K and mTOR were inhibited by PD. In addition, the activation of PI3K and mTOR decreased the protective effect of PD on oral mucosal cells. To conclude, the PI3K/mTOR signaling pathway was found to be inactivated, thereby restraining the activation of the full immune cell by inhibition of the pro-inflammatory cytokines, as revealed by the results indicating the prevention of the HG-induced inflammation response by PD.

Effect of extracellular hyperosmolality during normothermia and hyperthermia on the autophagic response in peripheral blood mononuclear cells from young men

Heat-stress induced dehydration is associated with extracellular hyperosmolality. To counteract the associated stress, cells employ cytoprotective mechanisms, including autophagy, however, the autophagic response to hyperosmotic stress has yet to be evaluated in humans. Thus, we investigated autophagy and associated cellular stress pathways (the heat shock response [HSR], apoptosis, and the acute inflammatory response) to isosmotic and hyperosmotic conditions with and without hyperthermia in twelve young men (mean [SD]; 25 [5] years). Participants received a 90-min intravenous infusion of either isosmotic (ISO; 0.9% NaCl; serum osmolality of 293 [4] mOsm/kg) or hyperosmotic (HYP; 3.0% NaCl; 300 [6] mOsm/kg) saline, followed by passive whole-body heating using a water perfused suit to increase esophageal temperature by ~0.8⁰C. Peripheral blood mononuclear cells were harvested at baseline (pre-infusion), post-infusion, and after heating, and changes in protein content were analyzed via Western blotting. Post-infusion, the LC3-II/I ratio was higher in HYP compared to ISO infusion (p<0.001), although no other protein changes were observed (all p>0.050). Following passive heating, autophagy increased in HYP, as demonstrated by an increase in LC3-II from baseline (p=0.004) and an elevated LC3-II/I ratio compared to ISO (p=0.035), and a decrease in p62 when compared to the ISO condition (p=0.019). This was accompanied by an elevation in cleaved caspase-3 following heating in the HYP condition (p<0.010), however, the HSR and acute inflammatory response did not change under any condition (all p>0.050). Taken together, our findings indicate that serum hyperosmolality induces autophagy and apoptotic signaling during mild hyperthermia with minimal autophagic activation during normothermia.

Handelin extends lifespan and healthspan of Caenorhabditis elegans by reducing ROS generation and improving motor function

Aging and aging-related disorders contribute to formidable socioeconomic and healthcare challenges. Several promising small molecules have been identified to target conserved genetic pathways delaying aging to extend lifespan and healthspan in many organisms. We previously found that extract from an edible and medicinal plant Chrysanthemum indicum L. (C. indicum L.) protect skin from UVB-induced photoaging, partially by reducing reactive oxygen species (ROS) generation. Thus, we hypothesized that C. indicum L. and its biological active compound may extend lifespan and health span in vivo. We find that both water and ethanol extracts from C. indicum L. extended lifespan of Caenorhabditis elegans, with better biological effect on life extending for ethanol extracts. As one of the major biological active compounds, handelin extended lifespan of C. elegans too. RNA-seq analysis revealed overall gene expression change of C. elegans post stimulation of handelin focus on several antioxidative proteins. Handelin significantly reduced ROS level and maintained the number and morphology of mitochondria. Moreover, handelin improveed many C. elegans behaviors related to healthspan, including increased pharyngeal pumping and body movement. Muscle fiber imaging analyses revealed that handelin maintains muscle architecture by stabilizing myofilaments. In conclusion, our present study finds a novel compound handelin, from C. indicum L., which bring about biologically beneficial effects by mild stress response, termed as hormetin, that can extend both lifespan and healthspan in vivo on C. elegans. Further study on mammal animal model of natural aging or sarcopenia will verify the potential clinical value of handelin.