Suppressing Hippo signaling in the stem cell niche promotes skeletal muscle regeneration

Angiotensin II type-2 receptor signaling facilitates liver injury repair and regeneration via inactivation of Hippo pathway

The angiotensin II type 2 receptor (AT2R) is a well-established component of the renin-angiotensin system and is known to counteract classical activation of this system and protect against organ damage. Pharmacological activation of the AT2R has significant therapeutic benefits, including vasodilation, natriuresis, anti-inflammatory activity, and improved insulin sensitivity. However, the precise biological functions of the AT2R in maintaining homeostasis in liver tissue remain largely unexplored. In this study, we found that the AT2R facilitates liver repair and regeneration following acute injury by deactivating Hippo signaling and that interleukin-6 transcriptionally upregulates expression of the AT2R in hepatocytes through STAT3 acting as a transcription activator binding to promoter regions of the AT2R. Subsequently, elevated AT2R levels activate downstream signaling via heterotrimeric G protein Gα12/13-coupled signals to induce Yap activity, thereby contributing to repair and regeneration processes in the liver. Conversely, a deficiency in the AT2R attenuates regeneration of the liver while increasing susceptibility to acetaminophen-induced liver injury. Administration of an AT2R agonist significantly enhances the repair and regeneration capacity of injured liver tissue. Our findings suggest that the AT2R acts as an upstream regulator in the Hippo pathway and is a potential target in the treatment of liver damage.

Therapeutic angiogenesis and tissue revascularization in ischemic vascular disease

Ischemic vascular disease is a major healthcare problem. The keys to treatment lie in vascular regeneration and restoration of perfusion. However, current treatments cannot satisfy the need for vascular regeneration to restore blood circulation. As biomedical research has evolved rapidly, a variety of potential alternative therapeutics has been explored widely, such as growth factor-based therapy, cell-based therapy, and material-based therapy including nanomedicine and biomaterials. This review will comprehensively describe the main pathogenesis of vascular injury in ischemic vascular disease, the therapeutic function of the above three treatment strategies, the corresponding potential challenges, and future research directions.

PER1 promotes functional recovery of mice with hindlimb ischemia by inducing anti-inflammatory macrophage polarization

Hindlimb ischemia (HLI) is an arterial occlusive disease that exposes the patients to the risk of limb gangrene and loss. Polarization of macrophages is related to HLI-induced inflammation. Period circadian regulator 1 (PER1) is a core component of the circadian clock. We first showed, based upon bioinformatics analysis of microarray data, that PER1 expression was reduced in monocytes from patients with critical limb ischemia. The proximal femoral artery in the left hindlimb of male mice was ligated and then the femoral artery and its collateral branches were removed to establish the HLI mouse model. After modeling, a single intramuscular injection of 1 × 10⁹ pfu Ad-PER1 was performed at the adductor and gastrocnemius muscles. The gastrocnemius muscle tissues were collected at day 0, 3, 7, 14, 21 post-HLI. There was obvious pathological necrosis, accompanied with reduced expression of PER1 in the muscle tissues of HLI mice. Expression of CD68 and CD31 seemed to be corresponded to PER1 in gastrocnemius muscle, implying the potential of PER1 in regulating macrophage-related inflammation and angiogenesis. PER1 overexpression diminished myocyte damage, promoted blood flow restoration and improved behavioral scores of HLI mice. Immunostaining of CD31 and α-SMA revealed that PER1 upregulation reversed HLI-induced decreases in capillary and arteriole density. In vitro, RAW264.7 cells were cultured in hypoxia (1% O₂) for 24 h. The percentage of pro-inflammatory CD86⁺ macrophages (M1 type) was decreased and that of anti-inflammatory CD206+ macrophages (M2 type) was increased when PER1 was overexpressed. Moreover, the expression levels of TNF-α, IL-6 and M1-type marker iNOS were decreased, and levels of IL-10 and M2-type marker Arg-1 were increased by PER1 in gastrocnemius muscle of HLI mice and hypoxia-treated RAW264.7 cells. PER1 might reduce M1 macrophage polarization and promote M2 macrophage polarization, and thus exert anti-inflammatory and pro-angiogenic actions. Our findings suggest that PER1 overexpression promotes functional recovery of mice with HLI through regulating macrophage polarization.

Hippo pathway inhibition promotes metabolic adaptability and antioxidant response in myoblasts

Metabolic plasticity in a hostile environment ensures cell survival. We investigated whether Hippo pathway inhibition contributed to cell adaptations under challenging conditions. We examined metabolic profiles and fuel substrate choices and preferences in C2C12 myoblasts after Hippo pathway inhibition via Salvador knockdown (SAV1 KD). SAV1 KD induced higher ATP production and a more energetic phenotype. Bioenergetic profiling showed enhanced key mitochondrial parameters including spare respiratory capacity. SAV1 KD cells showed markedly elevated glycolysis and glycolytic reserves; blocking other fuel-oxidation pathways enhanced mitochondrial flexibility of glucose oxidation. Under limited glucose, endogenous fatty acid oxidation increased to cope with bioenergetic stress. Gene expression patterns after SAV1 KD suggested transcriptional upregulation of key metabolic network regulators to promote energy production and free radical scavenging that may prevent impaired lipid and glucose metabolism. In SAV1 KD cells, sirtuin signaling was the top enriched canonical pathway linked with enhanced mitochondrial ATP production. Collectively, we demonstrated that Hippo pathway inhibition in SAV1 KD cells induces multiple metabolic properties, including enhancing mitochondrial spare respiratory capacity or glycolytic reserve to cope with stress and upregulating metabolic pathways supporting elevated ATP demand, bioenergetics, and glycolysis and counteracting oxidative stress. In response to metabolic challenges, SAV1 KD cells can increase fatty acid oxidation or glucose-coupled oxidative phosphorylation capacity to compensate for substrate limitations or alternative fuel oxidation pathway inhibition.

Molecular mechanisms of exercise contributing to tissue regeneration

Physical activity has been known as an essential element to promote human health for centuries. Thus, exercise intervention is encouraged to battle against sedentary lifestyle. Recent rapid advances in molecular biotechnology have demonstrated that both endurance and resistance exercise training, two traditional types of exercise, trigger a series of physiological responses, unraveling the mechanisms of exercise regulating on the human body. Therefore, exercise has been expected as a candidate approach of alleviating a wide range of diseases, such as metabolic diseases, neurodegenerative disorders, tumors, and cardiovascular diseases. In particular, the capacity of exercise to promote tissue regeneration has attracted the attention of many researchers in recent decades. Since most adult human organs have a weak regenerative capacity, it is currently a key challenge in regenerative medicine to improve the efficiency of tissue regeneration. As research progresses, exercise-induced tissue regeneration seems to provide a novel approach for fighting against injury or senescence, establishing strong theoretical basis for more and more "exercise mimetics." These drugs are acting as the pharmaceutical alternatives of those individuals who cannot experience the benefits of exercise. Here, we comprehensively provide a description of the benefits of exercise on tissue regeneration in diverse organs, mainly focusing on musculoskeletal system, cardiovascular system, and nervous system. We also discuss the underlying molecular mechanisms associated with the regenerative effects of exercise and emerging therapeutic exercise mimetics for regeneration, as well as the associated opportunities and challenges. We aim to describe an integrated perspective on the current advances of distinct physiological mechanisms associated with exercise-induced tissue regeneration on various organs and facilitate the development of drugs that mimics the benefits of exercise.

Skeletal Muscle Regeneration in Cardiotoxin-Induced Muscle Injury Models

Skeletal muscle injuries occur frequently in daily life and exercise. Understanding the mechanisms of regeneration is critical for accelerating the repair and regeneration of muscle. Therefore, this article reviews knowledge on the mechanisms of skeletal muscle regeneration after cardiotoxin-induced injury. The process of regeneration is similar in different mouse strains and is inhibited by aging, obesity, and diabetes. Exercise, microcurrent electrical neuromuscular stimulation, and mechanical loading improve regeneration. The mechanisms of regeneration are complex and strain-dependent, and changes in functional proteins involved in the processes of necrotic fiber debris clearance, M1 to M2 macrophage conversion, SC activation, myoblast proliferation, differentiation and fusion, and fibrosis and calcification influence the final outcome of the regenerative activity.

Mst1/2 is necessary for satellite cell differentiation to promote muscle regeneration

The diminished ability for muscle to regenerate is associated with aging, diabetes and cancers. Muscle regeneration depends on the activation and differentiation of satellite cells (SCs). Inactivation of Mst1/2 promotes cell proliferation by activating Yap, and that has been reported as a potential therapeutic target for improving many organ regeneration. However, the function of Mst1/2 in SCs fate decision and that effect on muscle regeneration remain unknown. By using inducible conditional knockout Mst1/2 in the SCs of mice and an inhibitor of Mst1/2, we found that inhibition of Mst1/2 in SCs significantly decrease Yap phosphorylation, thus causing Yap to accumulate in the nucleus and impairing SC differentiation; Mst1/2 were slightly elevated by irisin stimulation during SC differentiation; but inhibiting Mst1/2 in SCs significantly impaired irisin-induced muscle regeneration. These results indicate that Mst1/2 is necessary for SC differentiation and inhibiting Mst1/2 as a therapeutic target has potential risks for muscle regeneration.