Murine myoblast migration: influence of replicative ageing and nutrition

Augmented mitochondrial apoptotic signaling impairs C2C12 myoblast differentiation following cellular aging through sequential passaging

Aging is associated with the steady decline of several cellular processes. The loss of skeletal muscle mass, termed sarcopenia, is one of the major hallmarks of aging. Aged skeletal muscle exhibits a robust reduction in its regenerative capacity due to dysfunction (i.e., senescence, lack of self-renewal, and impaired differentiation) of resident muscle stem cells, called satellite cells. To replicate aging in vitro, immortalized skeletal muscle cells (myoblasts) can be treated with various agents to mimic age-related dysfunction; however, these come with their own set of limitations. In the present study, we used sequential passaging of mouse myoblasts to mimic impaired differentiation that is observed in aged skeletal muscle. Further, we investigated mitochondrial apoptotic mechanisms to better understand the impaired differentiation in these "aged" cells. Our data shows that sequential passaging (>20 passages) of myoblasts is accompanied with significant reductions in differentiation and elevated cell death. Furthermore, high-passage (HP) myoblasts exhibit greater mitochondrial-mediated apoptotic signaling through mitochondrial BAX translocation, CYCS and AIFM1 release, and caspase-9 activation. Finally, we show that inhibition of mitochondrial outer membrane permeability partly recovered differentiation in HP myoblasts. Together, our findings suggests that mitochondrial apoptotic signaling is a contributing factor to the diminished differentiation that is observed in aged myoblasts.

Degradation of ribosomal and chaperone proteins is attenuated during the differentiation of replicatively aged C2C12 myoblasts

BACKGROUND

Cell assays are important for investigating the mechanisms of ageing, including losses in protein homeostasis and 'proteostasis collapse'. We used novel isotopic labelling and proteomic methods to investigate protein turnover in replicatively aged (>140 population doublings) murine C2C12 myoblasts that exhibit impaired differentiation and serve as a model for age-related declines in muscle homeostasis.

METHODS

The Absolute Dynamic Profiling Technique for Proteomics (Proteo-ADPT) was used to investigate proteostasis in young (passage 6-10) and replicatively aged (passage 48-50) C2C12 myoblast cultures supplemented with deuterium oxide (D₂ O) during early (0-24 h) or late (72-96 h) periods of differentiation. Peptide mass spectrometry was used to quantify the absolute rates of abundance change, synthesis and degradation of individual proteins.

RESULTS

Young cells exhibited a consistent ~25% rise in protein accretion over the 96-h experimental period. In aged cells, protein accretion increased by 32% (P < 0.05) during early differentiation, but then fell back to baseline levels by 96-h. Proteo-ADPT encompassed 116 proteins and 74 proteins exhibited significantly (P < 0.05, FDR < 5% interaction between age × differentiation stage) different changes in abundance between young and aged cells at early and later periods of differentiation, including proteins associated with translation, glycolysis, cell-cell adhesion, ribosomal biogenesis, and the regulation of cell shape. During early differentiation, heat shock and ribosomal protein abundances increased in aged cells due to suppressed degradation rather than heightened synthesis. For instance, HS90A increased at a rate of 10.62 ± 1.60 ng/well/h in aged which was significantly greater than the rate of accretion (1.86 ± 0.49 ng/well/h) in young cells. HS90A synthesis was similar in young (21.23 ± 3.40 ng/well/h) and aged (23.69 ± 1.13 ng/well/h), but HS90A degradation was significantly (P = 0.05) greater in young (19.37 ± 2.93 ng/well/h) versus aged (13.06 ± 0.76 ng/well/h) cells. During later differentiation the HS90A degradation (8.94 ± 0.38 ng/well/h) and synthesis (7.89 ± 1.28 ng/well/h) declined and were significantly less than the positive net balance between synthesis and degradation (synthesis = 28.14 ± 3.70 ng/well/h vs. degradation = 21.49 ± 3.13 ng/well/h) in young cells.

CONCLUSIONS

Our results suggest a loss of proteome quality as a precursor to the lack of fusion of aged myoblasts. The quality of key chaperone proteins, including HS90A, HS90B and HSP7C was reduced in aged cells and may account for the disruption to cell signalling required for the later stages of differentiation and fusion.

Cinnamaldehyde attenuates kidney senescence and injury through PI3K/Akt pathway-mediated autophagy via downregulating miR-155

Background

To prove the internal connection, we deciphered the effect of cinnamaldehyde on kidney senescence through establishing animal and cell models.

Methods

In vivo, a rat senescence model was constructed using D-galactose (D-gal), and the modeled rats were further treated with cinnamaldehyde. In vitro, rat renal tubular epithelial cells (NRK-52E) were transfected with miR-155 mimic or inhibitor and then treated with cinnamaldehyde, D-gal or PI3K inhibitor (LY294002). The serum levels of blood urea nitrogen (BUN) and serum creatinine (Scr) of the rats were measured by an automatic biochemical analyzer. Pathological changes of kidney were determined by hematoxylin-eosin staining. The senescence and viability of NRK-52E cells were assessed by SA-β-gal staining and CCK-8 assay, respectively. The levels of miR-155, p-PI3K/PI3K, p-Akt/Akt, LC3B (LC3-II and LC3-I) and Beclin1 were detected by qRT-PCR, immunohistochemistry, or western blot.

Results

D-gal elevated the levels of BUN, Scr and miR-155 in the kidney, induced the renal pathological damage, inhibited the cell viability, increased the numbers of SA-β-gal-, LC3B- and Beclin1-positive cells and upregulated the levels of LC3-II/LC3-I and Beclin1 both in the kidney and cells. Cinnamaldehyde reversed D-gal-induced effects on the kidney and cells, and moreover, the cinnamaldehyde-induced anti-D-gal effects on cells could be suppressed by miR-155 mimic but promoted by miR-155 inhibitor. LY294002 potentiated D-gal-induced effects, and reversed cinnamaldehyde- and miR-155 inhibitor-caused impacts on the PI3K/Akt pathway and LC3-II/LC3-I level in D-gal-induced cells.

Conclusion

Cinnamaldehyde attenuates kidney senescence and injury through PI3K/Akt pathway-mediated autophagy via downregulating miR-155.

Pannexin Channel Regulation of Cell Migration: Focus on Immune Cells

The role of Pannexin (PANX) channels during collective and single cell migration is increasingly recognized. Amongst many functions that are relevant to cell migration, here we focus on the role of PANX-mediated adenine nucleotide release and associated autocrine and paracrine signaling. We also summarize the contribution of PANXs with the cytoskeleton, which is also key regulator of cell migration. PANXs, as mechanosensitive ATP releasing channels, provide a unique link between cell migration and purinergic communication. The functional association with several purinergic receptors, together with a plethora of signals that modulate their opening, allows PANX channels to integrate physical and chemical cues during inflammation. Ubiquitously expressed in almost all immune cells, PANX1 opening has been reported in different immunological contexts. Immune activation is the epitome coordination between cell communication and migration, as leukocytes (i.e., T cells, dendritic cells) exchange information while migrating towards the injury site. In the current review, we summarized the contribution of PANX channels during immune cell migration and recruitment; although we also compile the available evidence for non-immune cells (including fibroblasts, keratinocytes, astrocytes, and cancer cells). Finally, we discuss the current evidence of PANX1 and PANX3 channels as a both positive and/or negative regulator in different inflammatory conditions, proposing a general mechanism of these channels contribution during cell migration.

Cellular dynamics of myogenic cell migration: molecular mechanisms and implications for skeletal muscle cell therapies

Directional cell migration is a critical process underlying morphogenesis and post-natal tissue regeneration. During embryonic myogenesis, migration of skeletal myogenic progenitors is essential to generate the anlagen of limbs, diaphragm and tongue, whereas in post-natal skeletal muscles, migration of muscle satellite (stem) cells towards regions of injury is necessary for repair and regeneration of muscle fibres. Additionally, safe and efficient migration of transplanted cells is critical in cell therapies, both allogeneic and autologous. Although various myogenic cell types have been administered intramuscularly or intravascularly, functional restoration has not been achieved yet in patients with degenerative diseases affecting multiple large muscles. One of the key reasons for this negative outcome is the limited migration of donor cells, which hinders the overall cell engraftment potential. Here, we review mechanisms of myogenic stem/progenitor cell migration during skeletal muscle development and post-natal regeneration. Furthermore, strategies utilised to improve migratory capacity of myogenic cells are examined in order to identify potential treatments that may be applied to future transplantation protocols.

CCR3 antagonist protects against induced cellular senescence and promotes rejuvenation in periodontal ligament cells for stimulating pulp regeneration in the aged dog

Pulp regeneration after transplantation of mobilized dental pulp stem cells (MDPSCs) declines in the aged dogs due in part to the chronic inflammation and/or cellular senescence. Eotaxin-1/C-C motif chemokine 11 (CCL11) is an inflammation marker via chemokine receptor 3 (CCR3). Moreover, CCR3 antagonist (CCR3A) can inhibit CCL11 binding to CCR3 and prevent CCL11/CCR3 signaling. The study aimed to examine the effect of CCR3A on cellular senescence and anti-inflammation/immunomodulation in human periodontal ligament cells (HPDLCs). The rejuvenating effects of CCR3A on neurite extension and migratory activity to promote pulp regeneration in aged dog teeth were also evaluated. In vivo, the amount of regenerated pulp tissues was significantly increased by transplantation of MDPSCs with CCR3A compared to control without CCR3A. In vitro, senescence of HPDLCs was induced after p-Cresol exposure, as indicated by increased cell size, decreased proliferation and increased senescence markers, p21 and IL-1β. Treatment of HPDLCs with CCR3A prevented the senescence effect of p-Cresol. Furthermore, CCR3A significantly decreased expression of CCL11, increased expression of immunomodulatory factor, IDO, and enhanced neurite extension and migratory activity. In conclusion, CCR3A protects against p-Cresol-induced cellular senescence and enhances rejuvenating effects, suggesting its potential utility to stimulate pulp regeneration in the aged teeth.