MiR-29ab1 Cluster Resists Muscle Atrophy Through Inhibiting MuRF1.

Skeletal muscle has great plasticity. An increase in protein degradation can cause muscle atrophy. Atrogin-1 and muscle ring finger-1 (MuRF1) are dramatically upregulated in various muscle atrophy. Inhibition of Atrogin-1 and MuRF1 protects against muscle atrophy. MiR-29 plays an important regulatory role in skeletal muscle development. However, the function of miR-29 in skeletal muscle protein metabolism is not clear. To investigate the function of miR-29, we generated miR-29 knockout mice and the miR-29ab1 cluster overexpression mice. The disruption of miR-29 led to severe atrophy of skeletal muscle during puberty, and the muscle-specific overexpression of the miR-29ab1 cluster protected against denervation-induced and fasting-induced muscle atrophy. Furthermore, the overexpression of miR-29a, b mimics in myotubes resisted the muscle atrophy. MuRF1 was the direct target gene of miR-29a, b. These results demonstrate that miR-29ab1 cluster plays a critical role in the maintenance of skeletal muscle. MiR-29ab1 cluster is the excellent inhibitor of MuRF1, ultimately indicating that miR-29ab1 cluster is good therapeutic molecule candidate for adulthood.

TMEM79/MATTRIN defines a pathway for Frizzled regulation and is required for Xenopus embryogenesis.

Wnt signaling through the Frizzled (FZD) family of serpentine receptors is essential for embryogenesis and homeostasis, and stringent control of the FZD protein level is critical for stem cell regulation. Through CRISPR/Cas9 genome-wide screening in human cells, we identified TMEM79/MATTRIN, an orphan multi-span transmembrane protein, as a specific inhibitor of Wnt/FZD signaling. TMEM79 interacts with FZD during biogenesis and promotes FZD degradation independent of ZNRF3/RNF43 ubiquitin ligases (R-spondin receptors). TMEM79 interacts with ubiquitin-specific protease 8 (USP8), whose activating mutations underlie human tumorigenesis. TMEM79 specifically inhibits USP8 deubiquitination of FZD, thereby governing USP8 substrate specificity and promoting FZD degradation. Tmem79 and Usp8 genes have a pre-bilaterian origin, and Tmem79 inhibition of Usp8 and Wnt signaling is required for anterior neural development and gastrulation in Xenopus embryos. TMEM79 is a predisposition gene for Atopic dermatitis, suggesting deregulation of Wnt/FZD signaling a possible cause for this most common yet enigmatic inflammatory skin disease.

Fate decision of satellite cell differentiation and self-renewal by miR-31-IL34 axis.

Quiescent satellite cells (SCs) that are activated to produce numerous myoblasts underpin the complete healing of damaged skeletal muscle. How cell-autonomous regulatory mechanisms modulate the balance among cells committed to differentiation and those committed to self-renewal to maintain the stem cell pool remains poorly explored. Here, we show that miR-31 inactivation compromises muscle regeneration in adult mice by impairing the expansion of myoblasts. miR-31 is pivotal for SC proliferation, and its deletion promotes asymmetric cell fate segregation of proliferating cells, resulting in enhanced myogenic commitment and re-entry into quiescence. Further analysis revealed that miR-31 posttranscriptionally suppresses interleukin 34 (IL34) mRNA, the protein product of which activates JAK-STAT3 signaling required for myogenic progression. IL34 inhibition rescues the regenerative deficiency of miR-31 knockout mice. Our results provide evidence that targeting miR-31 or IL34 activities in SCs could be used to counteract the functional exhaustion of SCs in pathological conditions.

miR-29a/b1 Inhibits Hair Follicle Stem Cell Lineage Progression by Spatiotemporally Suppressing WNT and BMP Signaling.

Hair follicle stem cells (HFSCs) and subsequent generations of matrix progeny make lineage choices by responding to spatiotemporal signals; however, the cues driving that specification are not well understood. Here, we demonstrate that the dynamics of microRNA (miR)-29 expression are inversely proportional to HFSC lineage progression. Furthermore, we show that sustained miR-29a/b1 overexpression in anagen or telogen in mice causes a short-hair phenotype and eventual hair loss by inhibiting the proliferation of HFSCs and matrix cells and likely preventing their differentiation. Conversely, in a loss-of-function in vivo model, miR-29a/b1 deficiency accelerates HFSC lineage progression in telogen. Mechanistically, miR-29a/b1 blocks HFSC lineage specification by spatiotemporally targeting Ctnnb1, Lrp6, Bmpr1a, and Ccna2. We further show that skin-specific Lrp6 or Bmpr1a ablation partially accounts for the short-hair phenotype. Overall, these synergistic targets reveal miR-29a/b1 as a high-fidelity antagonist of HFSC lineage progression and a potential therapeutic target for hair loss.

Overexpression of miR-29 Leads to Myopathy that Resemble Pathology of Ullrich Congenital Muscular Dystrophy.

Ullrich congenital muscular dystrophy (UCMD) bring heavy burden to patients' families and society. Because the incidence of this disease is very low, studies in patients are extremely limited. Animal models of this disease are indispensable. UCMD belongs to extracellular matrix-related diseases. However, the disease models constructed by knocking out some pathogenic genes of human, such as the Col6a1, Col6a2, or Col6a3 gene, of mice could not mimic UCMD. The purpose of this study is to construct a mouse model which can resemble the pathology of UCMD. miR-29 is closely related to extracellular matrix deposition of tissues and organs. To address this issue, we developed a mouse model for overexpression miR-29 using Tet-on system. In the muscle-specific miR-29ab1 cluster transgenic mice model, we found that mice exhibited dyskinesia, dyspnea, and spinal anomaly. The skeletal muscle was damaged and regenerated. At the same time, we clarify the molecular mechanism of the role of miR-29 in this process. Different from human, Col4a1 and Col4a2, target genes of miR-29, are the key pathogenic genes associating with these phenotypes. This mouse model simulates the human clinical and pathological characteristics of UCMD patients and is helpful for the subsequent research and treatment of UCMD.

Islr regulates canonical Wnt signaling-mediated skeletal muscle regeneration by stabilizing Dishevelled-2 and preventing autophagy.

Satellite cells are crucial for skeletal muscle regeneration, but the molecular mechanisms regulating satellite cells are not entirely understood. Here, we show that the immunoglobulin superfamily containing leucine-rich repeat (Islr), a newly identified marker for mesenchymal stem cells, stabilizes canonical Wnt signaling and promote skeletal muscle regeneration. Loss of Islr delays skeletal muscle regeneration in adult mice. In the absence of Islr, myoblasts fail to develop into mature myotubes due to defective differentiation. Islr interacts with Dishevelled-2 (Dvl2) to activate canonical Wnt signaling, consequently regulating the myogenic factor myogenin (MyoG). Furthermore, Islr stabilizes Dvl2 by reducing the level of LC3-labeled Dvl2 and preventing cells from undergoing autophagy. Together, our findings identify Islr as an important regulator for skeletal muscle regeneration.

miRNA-34c inhibits myoblasts proliferation by targeting YY1.

miRNAs are increasingly being implicated as key regulators of cell proliferation, apoptosis, and differentiation. miRNA-34c appears to play a crucial role in cancer pathogenesis wherein it exerts its effect as a tumor suppressor. However, the role of miR-34c in myoblast proliferation remains poorly understood. Here, we found that overexpression miR-34c inhibited myoblasts proliferation by reducing the protein and mRNA expression of cell cycle genes. In contrast, blocking the function of miR-34c promoted myoblasts proliferation and increased the protein and mRNA expression of cell cycle genes. Moreover, miR-34c directly targeted YY1 and inhibited its expression. Similar to overexpression miR-34c, knockdown of YY1 by siRNA suppressed myoblasts proliferation. Our study provides novel evidence for a role of miR-34c in inhibiting myoblasts proliferation by repressing YY1. Thus, miR-34c has the potential to be used to enhance skeletal muscle development and regeneration.