Lin28a maintains a subset of adult muscle stem cells in an embryonic-like state.

During homeostasis and after injury, adult muscle stem cells (MuSCs) activate to mediate muscle regeneration. However, much remains unclear regarding the heterogeneous capacity of MuSCs for self-renewal and regeneration. Here, we show that Lin28a is expressed in embryonic limb bud muscle progenitors, and that a rare reserve subset of Lin28a+Pax7- skeletal MuSCs can respond to injury at adult stage by replenishing the Pax7+ MuSC pool to drive muscle regeneration. Compared with adult Pax7+ MuSCs, Lin28a+ MuSCs displayed enhanced myogenic potency in vitro and in vivo upon transplantation. The epigenome of adult Lin28a+ MuSCs showed resemblance to embryonic muscle progenitors. In addition, RNA-sequencing revealed that Lin28a+ MuSCs co-expressed higher levels of certain embryonic limb bud transcription factors, telomerase components and the p53 inhibitor Mdm4, and lower levels of myogenic differentiation markers compared to adult Pax7+ MuSCs, resulting in enhanced self-renewal and stress-response signatures. Functionally, conditional ablation and induction of Lin28a+ MuSCs in adult mice revealed that these cells are necessary and sufficient for efficient muscle regeneration. Together, our findings connect the embryonic factor Lin28a to adult stem cell self-renewal and juvenile regeneration.

Adult progenitor rejuvenation with embryonic factors.

During ageing, adult stem cells' regenerative properties decline, as they undergo replicative senescence and lose both their proliferative and differentiation capacities. In contrast, embryonic and foetal progenitors typically possess heightened proliferative capacities and manifest a more robust regenerative response upon injury and transplantation, despite undergoing many rounds of mitosis. How embryonic and foetal progenitors delay senescence and maintain their proliferative and differentiation capacities after numerous rounds of mitosis, remains unknown. It is also unclear if defined embryonic factors can rejuvenate adult progenitors to confer extended proliferative and differentiation capacities, without reprogramming their lineage-specific fates or inducing oncogenic transformation. Here, we report that a minimal combination of LIN28A, TERT, and sh-p53 (LTS), all of which are tightly regulated and play important roles during embryonic development, can delay senescence in adult muscle progenitors. LTS muscle progenitors showed an extended proliferative capacity, maintained a normal karyotype, underwent myogenesis normally, and did not manifest tumorigenesis nor aberrations in lineage differentiation, even in late passages. LTS treatment promoted self-renewal and rescued the pro-senescence phenotype of aged cachexia patients' muscle progenitors, and promoted their engraftment for skeletal muscle regeneration in vivo. When we examined the mechanistic basis for LIN28A's role in the LTS minimum combo, let-7 microRNA suppression could not fully explain how LIN28A promoted muscle progenitor self-renewal. Instead, LIN28A was promoting the translation of oxidative phosphorylation mRNAs in adult muscle progenitors to optimize mitochondrial reactive oxygen species (mtROS) and mitohormetic signalling. Optimized mtROS induced a variety of mitohormetic stress responses, including the hypoxic response for metabolic damage, the unfolded protein response for protein damage, and the p53 response for DNA damage. Perturbation of mtROS levels specifically abrogated the LIN28A-driven hypoxic response in Hypoxia Inducible Factor-1α (HIF1α) and glycolysis, and thus LTS progenitor self-renewal, without affecting normal or TS progenitors. Our findings connect embryonically regulated factors to mitohormesis and progenitor rejuvenation, with implications for ageing-related muscle degeneration.

Endocytosis-mediated triple-activable prodrug nanotherapeutics potentiating therapeutic efficacy and security towards solid tumors.

Self-assembling prodrug nanotherapeutics have emerged as a promising nanoplatform for anticancer drug delivery. The specific and efficient activation of prodrug nanotherapeutics inside tumor cells is vital for the antitumor efficacy and security. Herein, a triple-activable prodrug polymer (TAP) is synthesized by conjugating polyethylene glycol-poly-(caprolactone)-paclitaxel (PTX) polymer with two tumor-responsive bonds, disulfide and acetal. TAP could self-assemble into nanotherapeutics (TAP NTs) free of surfactant with a high drug loading (32.6%). In blood circulation, TAP NTs could remain intact to efficiently accumulate in tumor sites. Thereafter, tumor cells would internalize TAP NTs through multiple endocytosis pathways. Inside tumor cells, TAP NTs could be activated to release PTX and induce tumor cell apoptosis in triple pathways: (i) lysosomal acidity rapid activation; (ii) ROS-acidity tandem activation and (iii) GSH-acidity tandem activation. Compared with Taxol and non-activable control, TAP NTs significantly potentiate the antitumor efficacy and security of PTX against solid tumors including breast cancer and colon cancer.

Machine learning-based phenotypic screening for postmitotic growth inducers uncover vitamin D3 metabolites as small molecule ribosome agonists.

OBJECTIVES: To restore tissue growth without increasing the risk for cancer during aging, there is a need to identify small molecule drugs that can increase cell growth without increasing cell proliferation. While there have been numerous high-throughput drug screens for cell proliferation, there have been few screens for post-mitotic anabolic growth. MATERIALS AND METHODS: A machine learning (ML)-based phenotypic screening strategy was used to discover metabolites that boost muscle growth. Western blot, qRT-PCR and immunofluorescence staining were used to evaluate myotube hypertrophy/maturation or protein synthesis. Mass spectrometry (MS)-based thermal proteome profiling-temperature range (TPP-TR) technology was used to identify the protein targets that bind the metabolites. Ribo-MEGA size exclusion chromatography (SEC) analysis was used to verify whether the ribosome proteins bound to calcitriol. RESULTS: We discovered both the inactive cholecalciferol and the bioactive calcitriol are amongst the top hits that boost post-mitotic growth. A large number of ribosomal proteins' melting curves were affected by calcitriol treatment, suggesting that calcitriol binds to the ribosome complex directly. Purified ribosomes directly bound to pure calcitriol. Moreover, we found that calcitriol could increase myosin heavy chain (MHC) protein translation and overall nascent protein synthesis in a cycloheximide-sensitive manner, indicating that calcitriol can directly bind and enhance ribosomal activity to boost muscle growth. CONCLUSION: Through the combined strategy of ML-based phenotypic screening and MS-based omics, we have fortuitously discovered a new class of metabolite small molecules that can directly activate ribosomes to promote post-mitotic growth.

Pathogenesis of sarcopenia and the relationship with fat mass: descriptive review.

Age-associated obesity and muscle atrophy (sarcopenia) are intimately connected and are reciprocally regulated by adipose tissue and skeletal muscle dysfunction. During ageing, adipose inflammation leads to the redistribution of fat to the intra-abdominal area (visceral fat) and fatty infiltrations in skeletal muscles, resulting in decreased overall strength and functionality. Lipids and their derivatives accumulate both within and between muscle cells, inducing mitochondrial dysfunction, disturbing ß-oxidation of fatty acids, and enhancing reactive oxygen species (ROS) production, leading to lipotoxicity and insulin resistance, as well as enhanced secretion of some pro-inflammatory cytokines. In turn, these muscle-secreted cytokines may exacerbate adipose tissue atrophy, support chronic low-grade inflammation, and establish a vicious cycle of local hyperlipidaemia, insulin resistance, and inflammation that spreads systemically, thus promoting the development of sarcopenic obesity (SO). We call this the metabaging cycle. Patients with SO show an increased risk of systemic insulin resistance, systemic inflammation, associated chronic diseases, and the subsequent progression to full-blown sarcopenia and even cachexia. Meanwhile in many cardiometabolic diseases, the ostensibly protective effect of obesity in extremely elderly subjects, also known as the 'obesity paradox', could possibly be explained by our theory that many elderly subjects with normal body mass index might actually harbour SO to various degrees, before it progresses to full-blown severe sarcopenia. Our review outlines current knowledge concerning the possible chain of causation between sarcopenia and obesity, proposes a solution to the obesity paradox, and the role of fat mass in ageing.

Injectable chitosan thermogels for sustained and localized delivery of pingyangmycin in vascular malformations.

Pingyangmycin (PYM) is an effective drug to treat vascular malformations (VM), but can easily diffuse from the injection site, which will reduce its therapeutic effect and increase side effect. Our study was to evaluate PYM-loaded chitosan thermogels for sustained and localized embolization therapy. It was shown that in vitro release of PYM thermogels could be delayed up to 12 days. The results measured by MTT assay showed that PYM thermogels could inhibit proliferation and induce apoptosis of EA.hy926 cells in a concentration and time dependent manner. In vivo pharmacokinetics study demonstrated that compared with PYM injections, PYM thermogels had a better sustained delivery of PYM. Macroscopic observation and histological examination of rabbit ear veins displayed that after administration with PYM thermogels for 18 days, obvious venous embolization and inflammatory response could be found. These results indicate that PYM thermogels is likely to achieve excellent prospects for VM treatment.

Intravenous microemulsion of docetaxel containing an anti-tumor synergistic ingredient (Brucea javanica oil): formulation and pharmacokinetics.

The purpose of this study was to develop a docetaxel microemulsion containing an anti-tumor synergistic ingredient (Brucea javanica oil) and to investigate the characteristics of the microemulsion. Brucea javanica oil contains oleic acid and linoleic acids that have been shown by animal and human studies to inhibit tumor formation. The microemulsion containing Brucea javanica oil, medium-chain triglyceride, soybean lecithin, Solutol®HS 15, PEG 400, and water was developed for docetaxel intravenous administration. A formulation with higher drug content, lower viscosity, and smaller particle size was developed. The droplet size distribution of the dispersed phase of the optimized microemulsion was 13.5 nm, determined using a dynamic light scattering technique. The small droplet size enabled the microemulsion droplets to escape from uptake and phagocytosis by the reticuloendothelial system and increased the circulation time of the drug. The zeta potential was -41.3 mV. The optimized microemulsion was pale yellow, transparent, and non-opalescent in appearance. The value of the combination index was 0.58, showing that there was a synergistic effect when docetaxel was combined with Brucea javanica oil. After a single intravenous infusion dose (10 mg/kg) in male Sprague Dawley rats, the area under the curve of the microemulsion was higher and the half-time was longer compared with that of docetaxel solution alone, and showed superior pharmacokinetic characteristics. These results indicate that this preparation of docetaxel in emulsion is likely to provide an excellent prospect for clinical tumor treatment.

In vitro and in vivo evaluation of targeting efficiency of Adriamycin hydrochloride magnetic microspheres.

The objective of this study was to prepare magnetic microspheres as a targeting drug delivery system and to specifically evaluate its targeting efficiency. The magnetic microspheres were prepared by emulsion cross-linking techniques. Targeting efficiency was specifically investigated by experiments of biodistribution on rats and histological study. Adriamycin hydrochloride (ADR)-loaded magnetic microspheres were successfully prepared with the mean diameter of 3.853 µm (± 1.484 µm), and had its speciality of superparamagnetism. The results of the targeting efficiency study showed that application of the external magnetic field significantly increased the ADR concentration from 40.28 µg/ml to 100.70 µg/ml at 10 min, 36.99 µg/ml to 91.16 µg/ml at 60 min, and 13.71 µg/ml to 28.30 µg/ml at 180 min in liver as the targeting tissue. The relative uptake efficiencies in liver by injection treatment of ADR magnetic microspheres with external magnetic field were 3.87, 5.59, and 3.34 at 10 min, 60 min, and 180 min after administration, respectively. In conclusion, distinguished targeting efficiency was displayed, which indicated that the magnetic microspheres could be applied as a novel targeting drug delivery system.