Muscling in on stem cells

Myosteatosis for Early Detection of Muscle Disorder in Patients With Liver Cirrhosis

Background and aims

Muscle disorders in cirrhosis are associated with poor outcome and need early identification. Anthropometric measures lack sensitivity, and CT-based L3-skeletal muscle Index (L3-SMI) may miss early sarcopenia. The study aimed to find if SM-RA can identify more patients with muscle disorder than L3-SMI and anthropometry.

Methods

388 patients with cirrhosis underwent nutritional assessment by anthropometry, short-physical-performance-battery (SPPB) < 9, L3-SMI (<36.5 cm2/m2 (males); <30.2 cm2/m2 (females), and myosteatosis assessment by skeletal muscle radiation attenuation (SM-RA) (<41 HU for body mass index [BMI] <24.9 kg/m2 and <33 HU for ≥25 kg/m2) and results were compared.

Results

Sarcopenia based on SPPB was 38.9 % with scores (9 ± 1.48 vs. 10.74 ± 1.25, P = 0.001 in males; and 8.43 ± 1.59 vs. 9.89 ± 1.57, P = 0.001 in females). Mid-arm muscle circumference was lower in sarcopenic males [20.5 ± 2.42 vs. 22.9 ± 2.19 cm, P = 0.001] but not in females [19.4 ± 2.73 vs. 21.1 ± 2.51, P = 0.18]. L3-SMI-based sarcopenia was found in 44.8 % (additional 5.92 %) compared to SPPB, mostly in cryptogenic cirrhosis (19.2 % vs. 35.08 %, δ change +15.9 %). Myosteatosis (71.64 %) identified an additional 26.85 % and 32.74 % of patients with muscle disorder compared to L3SMI and SPPB, respectively, with the majority of new detection in non-alcoholic fatty liver disease (NAFLD) 39.4 % vs. 77.06 %, δ change +37.66 %) CTP-A patients (16.6 % vs. 36.8 %, δ change +20.2 %). Myosteatosis was found in 48.3 % of patients with normal L3-SMI.

Conclusion

SM-RA can identify more patients with muscle disorder than L3-SMI and SPPB.

Muscle quality, physical performance, and comorbidity are predicted by circulating procollagen type III N-terminal peptide (P3NP): the InCHIANTI follow-up study

Sarcopenia is characterized by skeletal muscle quantitative and qualitative alterations. A marker of collagen turnover, procollagen type III N-terminal peptide (P3NP), seems to be related to those conditions. This study aims to assess the predictive role of P3NP in muscle density and physical performance changes. In the InCHIANTI study, a representative sample from the registry lists of two towns in Tuscany, Italy, was recruited. Baseline data was collected in 1998, and follow-up visits were conducted every 3 years. Out of the 1453 participants enrolled at baseline, this study includes 1052 participants. According to P3NP median levels, population was clustered in two groups; 544 (51.7%) of the 1052 subjects included were classified in the low median levels (LM-P3NP); at the baseline, they were younger, had higher muscle density, and performed better at the Short Physical Performance Battery (SPPB), compared to the high-median group (HM-P3NP).LM-P3NP cases showed a lower risk to develop liver chronic diseases, CHF, myocardial infarction, and osteoarthritis. HM-P3NP levels were associated with a longitudinal reduction of muscle density, and this effect was potentiated by the interaction between P3NP and leptin. Moreover, variation in physical performance was inversely associated with high level of P3NP, and directly associated with high fat mass, and with the interaction between P3NP and muscle density. Our data indicate that P3NP is associated with the aging process, affecting body composition, physical performance, and clinical manifestations of chronic degenerative age-related diseases.

Human levator veli palatini muscle: a novel source of mesenchymal stromal cells for use in the rehabilitation of patients with congenital craniofacial malformations

Background

Bone reconstruction in congenital craniofacial differences, which affect about 2–3% of newborns, has long been the focus of intensive research in the field of bone tissue engineering. The possibility of using mesenchymal stromal cells in regenerative medicine protocols has opened a new field of investigation aimed at finding optimal sources of multipotent cells that can be isolated via non-invasive procedures. In this study, we analyzed whether levator veli palatini muscle fragments, which can be readily obtained in non-invasive manner during palatoplasty in cleft palate patients, represent a novel source of MSCs with osteogenic potential.

Methods

We obtained levator veli palatini muscle fragments (3–5 mm³), during surgical repair of cleft palate in 5 unrelated patients. Mesenchymal stromal cells were isolated from the muscle using a pre-plating technique and other standard practices. The multipotent nature of the isolated stromal cells was demonstrated via flow cytometry analysis and by induction along osteogenic, adipogenic, and chondrogenic differentiation pathways. To demonstrate the osteogenic potential of these cells in vivo, they were used to reconstruct a critical-sized full-thickness calvarial defect model in immunocompetent rats.

Results

Flow cytometry analysis showed that the isolated stromal cells were positive for mesenchymal stem cell antigens (CD29, CD44, CD73, CD90, and CD105) and negative for hematopoietic (CD34 and CD45) or endothelial cell markers (CD31). The cells successfully underwent osteogenic, chondrogenic, and adipogenic cell differentiation under appropriate cell culture conditions. Calvarial defects treated with CellCeram™ scaffolds seeded with the isolated levator veli palatini muscle cells showed greater bone healing compared to defects treated with acellular scaffolds.

Conclusion

Cells derived from levator veli palatini muscle have phenotypic characteristics similar to other mesenchymal stromal cells, both in vitro and in vivo. Our findings suggest that these cells may have clinical relevance in the surgical rehabilitation of patients with cleft palate and other craniofacial anomalies characterized by significant bone deficit.

Supplementary information

The online version contains supplementary material available at 10.1186/s13287-020-02017-7.

Plasma free amino acids are associated with sarcopenia in the course of hepatocellular carcinoma recurrence

OBJECTIVE

Sarcopenia worsens the prognosis of patients with hepatocellular carcinoma (HCC). The aim of this study was to elucidate the plasma free amino acids (PFAAs) associated with sarcopenia or myosteatosis in the course of HCC recurrence.

METHODS

In this cross-sectional study, 187 patients were enrolled retrospectively. All patients experienced more than one hospitalization (mean times, 2.65) owing to HCC recurrence. The skeletal muscle index (SMI) and muscle attenuation (MA) were measured by a transverse computed tomography (CT) scan image at the third lumbar vertebra (L3). The changes in the concentration of 24 PFAAs, SMI, and MA in the same patient between recurrences were defined as Δ. The associations between sarcopenia, myosteatosis, and PFAAs were evaluated by a logistic regression model. The ΔSMI and ΔMA were compared between the patients who received branched-chain amino acids (BCAAs) formulation and those who did not.

RESULTS

Patients with sarcopenia showed lower survival rate; the 1-, 3-, and 5-y survival rates were 85%, 42%, and 9%, respectively. Multivariate analysis revealed that the level of total BCAAs was significantly associated with sarcopenia. The correlation coefficient value between the change of leucine (ΔLeu) and ΔSMI was highest (R = 0.256; P < 0.001) among the PFAAs. In the Child-Pugh grade B or C, the decrease of SMI was significantly more suppressed in the patients with the BCAAs formulation than in those without BCAAs formulation (ΔSMI: mean change -0.98 versus -3.45 cm²/m²; P = 0.038).

CONCLUSION

Among the PFAAs, the level of BCAAs was associated with sarcopenia in the course of HCC recurrence.

Development of a 3D Tissue-Engineered Skeletal Muscle and Bone Co-culture System

In vitro 3D tissue-engineered (TE) structures have been shown to better represent in vivo tissue morphology and biochemical pathways than monolayer culture, and are less ethically questionable than animal models. However, to create systems with even greater relevance, multiple integrated tissue systems should be recreated in vitro. In the present study, the effects and conditions most suitable for the co-culture of TE skeletal muscle and bone are investigated. High-glucose Dulbecco's modified Eagle medium (HG-DMEM) supplemented with 20% fetal bovine serum followed by HG-DMEM with 2% horse serum is found to enable proliferation of both C2C12 muscle precursor cells and TE85 human osteosarcoma cells, fusion of C2C12s into myotubes, as well as an upregulation of RUNX2/CBFa1 in TE85s. Myotube formation is also evident within indirect contact monolayer cultures. Finally, in 3D co-cultures, TE85 collagen/hydroxyapatite constructs have significantly greater expression of RUNX2/CBFa1 and osteocalcin/BGLAP in the presence of collagen-based C2C12 skeletal muscle constructs; however, fusion within these constructs appears reduced. This work demonstrates the first report of the simultaneous co-culture and differentiation of 3D TE skeletal muscle and bone, and represents a significant step toward a full in vitro 3D musculoskeletal junction model.

Evidence for cervical muscle morphometric changes on magnetic resonance images after whiplash: A systematic review and meta-analysis

INTRODUCTION

Morphometric changes to cervical musculature in whiplash associated disorder have been reported in several studies with varying results. However, the evidence is not clear because only a limited number of cohorts have been studied and one cohort has been reported in multiple publications. The aim of this study was to assess the evidence for cervical muscle morphometric changes on magnetic resonance (MR) images after whiplash using a systematic review with meta-analysis.

MATERIALS AND METHODS

PubMed, MEDLINE and Cochrane Library were searched without language restriction using combinations of the MeSH terms "muscles", "whiplash injuries", and "magnetic resonance imaging". Studies of acute and chronic whiplash were included if they compared whiplash and control cervical spine muscle morphometry measurements from MR images. The search identified 380 studies. After screening, eight studies describing five cohorts (one acute, three chronic, one both acute and chronic) met the inclusion criteria. Participant characteristics and outcome measures were extracted using a standard extraction format. Quality of eligible studies was assessed using the Newcastle-Ottawa Scale. Muscle cross-sectional area (CSA) and fat infiltrate (MFI) for acute and chronic whiplash cohorts were compared using mean difference and 95% confidence intervals. Meta-analysis models were created when data from more than two eligible cohorts was available, using inverse-variance random-effects models (RevMan5 version 5.3.5).

RESULTS

Quality assessment was uniformly good but only two studies blinded the assessor. Analysis of the acute cohorts revealed no consensus with respect to CSA. MFI was not measured in the acute cohorts. Analysis of the chronic cohorts revealed CSA is probably increased in some muscles after whiplash but there is insufficient evidence to confirm whether MFI is also increased. Because the available data were limited, meta-analyses of only multifidus were performed. In chronic whiplash multifidus CSA was significantly increased at C5 (Z = 3.51, p < 0.01) and C6 (Z = 2.66, p < 0.01); and MFI was significantly increased at C7 only (Z = 2.52, p < 0.01) but the heterogeneity was unacceptably high (I² = 83%).

CONCLUSIONS

The strength of the evidence for cervical muscle morphometric changes on MR images after whiplash is inconsistent for CSA and MFI. Future study designs should be standardised with quantification of three-dimensional muscle morphometry.

Intramuscular Adipose Tissue and the Functional Components of Sarcopenia in Hospitalized Geriatric Patients

Intramuscular adipose tissue (IMAT) could be an important missing value in the assessment of sarcopenia. This study tries to determine the relation between IMAT, muscle strength, functionality and mortality. In addition, the relation with nutritional status is screened. For six months, all patients admitted to the University Geriatric Center of Antwerp were evaluated for strength (hand grip), functionality (short physical performance battery—SPPB) and nutritional status. After one year, patients/relatives were contacted to obtain a current health status (mortality). A total of 303 patients were included at a mean age of 83.0 ± 6.4 years. The mean percentage of IMAT was 29.2% ± 13.0% (range 3.2%–86.2%). There was a negative correlation between IMAT and both grip strength and SPPB. SPPB was positively correlated with both grip strength and muscle mass. There was a positive correlation between IMAT and mortality. There was a negative correlation between grip strength, SPPB and mortality. IMAT did not have a clear relation with nutritional status. IMAT should be addressed in the work-up of sarcopenia, as it is correlated with muscle strength, functionality and mortality. In this cohort of hospitalized geriatric patients, there is a mean of about one-third of measured muscle volume that appears to be adipose tissue.

Myosteatosis increases with aging and is associated with incident diabetes in African ancestry men

OBJECTIVE

Skeletal muscle fat infiltration (known as myosteatosis) is greater in African compared with European ancestry men and may play an important role in the development of type 2 diabetes (T2D). However, prospective studies examining the magnitude of changes in myosteatosis with aging and their metabolic consequences are sparse.

METHODS

Longitudinal changes in peripheral quantitative computed tomography measured calf myosteatosis [intermuscular fat (mm(2) ) and skeletal muscle density as a measure of intramuscular fat (mg/cm(3) )] were examined in 1515 Afro-Caribbean men aged 40+ years recruited without regard to their health status.

RESULTS

During an average of 6.2 years of follow-up, an age-related increase in intermuscular fat and a decrease in skeletal muscle density were observed (all P < 0.0001), which remained significant in those who lost weight, gained weight, or remained weight stable (all P < 0.0001). In addition, muscle density loss accelerated with increasing age (P < 0.0001). Increased intermuscular fat during follow-up was associated with an increased incident risk of T2D independent of factors known to be associated with T2D (odds ratios per 1-SD increase in intermuscular fat = 1.29; 95% CI = 1.08-1.53).

CONCLUSIONS

Our findings suggest that both inter- and intramuscular fat increase with advancing age and that intermuscular fat contributes to development of T2D among African ancestry men.

Emerging nanostructured materials for musculoskeletal tissue engineering

This review summarizes the recent developments in the preparation and applications of nanostructured materials for musculoskeletal tissue engineering.

The activation of satellite cells by nanofibrous poly ε-caprolacton constructs

Nanoscale patterning of scaffolds provides broad surface for adhesion and differentiation of stem cells. As we know, the combination of tissue engineering with stem cells technology hold the key for regeneration of damaged tissues for example skeletal muscle tissues. On the other hand, the mechanical assessments of poly ε-caprolacton nanofibers determined the required features of biomedical scaffold for skeletal muscle tissue. In this study, skeletal muscle satellite cells as the main group of stem cells were cultivated on the electrospun poly ε-caprolacton nanofibers. Our results indicated that in comparison with tissue culture polystyrene, the nanoscale of scaffolds provided more induction to matured cells of skeletal muscle. Moreover, the immobilization of cells by collagen on poly ε-caprolacton nanofibers significantly improved the differential potency of satellite cells.

Hierarchization of myogenic and adipogenic progenitors within human skeletal muscle

Skeletal muscle cells constitute a heterogeneous population that maintains muscle integrity through a high myogenic regenerative capacity. More unexpectedly, this population is also endowed with an adipogenic potential, even in humans, and intramuscular adipocytes have been found to be present in several disorders. We tested the distribution of myogenic and adipogenic commitments in human muscle-derived cells to decipher the cellular basis of the myoadipogenic balance. Clonal analysis showed that adipogenic progenitors can be separated from myogenic progenitors and, interestingly, from myoadipogenic bipotent progenitors. These progenitors were isolated in the CD34(+) population on the basis of the expression of CD56 and CD15 cell surface markers. In vivo, these different cell types have been found in the interstitial compartment of human muscle. In vitro, we show that the proliferation of bipotent myoadipogenic CD56(+)CD15(+) progenitors gives rise to myogenic CD56(+)CD15(-) progenitors and adipogenic CD56(-)CD15(+) progenitors. A cellular hierarchy of muscle and fat progenitors thus occurs within human muscle. These results provide cellular bases for adipogenic differentiation in human skeletal muscle, which may explain the fat development encountered in different muscle pathological situations.

Muscle-derived precursor cells isolated on the basis of differential adhesion properties respond differently to capillary flow

Capillary shear stress can improve osteogenic differentiation in muscle-derived precursor cells (MDPCs). This has implications for large-scale bioprocessing of cell therapies where capillary transfer is needed. The recovery, viability, and osteogenic differentiation potential of two subsets of MDPCs, early-adherent pre-plate 1 (PP1) and late-adherent PP3 populations, have been examined: PP1 MDPCs produced a greater degree of osteogenic differentiation than PP3 MDPCs, quantified by Alizarin Red S staining intensity (P < 0.05). For both cell populations, capillary flow-induced significant increases in Alizarin Red S staining (P < 0.05). However, PP1 cells were more susceptible to capillary flow-induced damage than PP3 cells and this was dependent on duration of exposure. Overall, results indicate that different cell subsets, even from within a single tissue, can respond variably to capillary shear stress, necessitating its precise monitoring and control.

Characterization of smooth muscle differentiation of purified human skeletal muscle-derived cells

The purpose of this study is to characterize the smooth muscle differentiation of purified human muscle-derived cells (hMDCs). The isolation and purification of hMDCs were conducted by modified preplate technique and Dynal CD34 cell selection. Smooth muscle cell differentiation was induced by the use of smooth muscle induction medium (SMIM) and low-serum medium. The gene expressions at the mRNA and protein levels of undifferentiated and differentiated hMDCs were tested by RT-PCR, Western blot and immunofluorescence studies. Western blot and immunofluorescence studies demonstrated the purified hMDCs cultured in SMIM for 4 weeks and expressed significant amount of smooth muscle myosin heavy chain (MHC) and α-smooth muscle actin (ASMA). The cells cultured in low-serum medium for 4 weeks also expressed ASMA, while the control group did not. RT-PCR analysis showed increased gene expression of smooth muscle markers, such as ASMA, Calponin, SM22, Caldesmon, Smoothelin and MHC when purified hMDCs were exposed to SMIM for 2 and 4 weeks when compared to the controls. In conclusion, we confirmed the smooth muscle differentiation capability of purified hMDCs. The gene expression of smooth muscle differentiation of purified hMDCs was characterized. These cells may be potential biomaterials for human tissue regeneration.

Effect of capillary shear stress on recovery and osteogenic differentiation of muscle-derived precursor cell populations

Both chemical and physical stimuli can influence the fate of precursor cell populations. Therefore, the impact they have on promoting unwanted differentiation events must be understood to improve the yield and purity of therapeutic cells for regenerative medicine approaches. Capillary shear forces, similar to those encountered during cell processing, can impact upon production of regenerative cell populations. As shear stress can promote osteogenic differentiation in adhered bone marrow-derived stromal cells, we sought to determine whether the same is true for populations of muscle-derived precursor cells (MDPCs) that were isolated from a muscle niche environment. We isolated MDPCs from craniofacial muscle of 5 day-old Royal College of Surgeons rats and subjected them to capillary shear events similar to those encountered during manual bioprocessing of cells. We then assessed whether viability and ectopic osteogenic differentiation of MDPCs was affected. We found that whilst immediate recovery of MDPCs was not significantly affected by shear, viability after 24 h was reduced in comparison to non-sheared MDPCs. By 48 h, sheared MDPCs had all recovered and had similar viability to non-sheared MDPCs. Ostegenic differentiation was enhanced following exposure to capillary shear in both osteogenic and myogenic medium. This indicates that shear forces similar to those encountered during the bioprocessing of cell populations for therapy can have a significant influence on the fate of MDPCs.

Epidemiology of myosteatosis

PURPOSE OF REVIEW

To summarize the epidemiology of myosteatosis and its association with diabetes.

RECENT FINDINGS

The role of myosteatosis (fat infiltration in skeletal muscle) in diabetes has received considerable attention. There is reasonably consistent evidence that myosteatosis contributes to glucose and insulin abnormalities and diabetes, possibly even independent of overall obesity. Novel hypotheses that link myosteatosis with insulin resistance and type 2 diabetes have also recently been proposed. These hypotheses suggest that impaired secretion of adipokines, modulation of nutritive blood flow to skeletal muscle, or both may be of importance for the development of myosteatosis. Recent longitudinal data also suggest that myosteatosis increases with aging, regardless of changes in body weight.

SUMMARY

Further studies are needed to identify the specific physiological mechanisms that influence myosteatosis, and the mechanisms that link this fat depot with insulin resistance. Longitudinal studies are also needed to evaluate the remodeling of skeletal muscle fat with aging, across a wider age spectrum, and across different populations, especially those at high risk of developing diabetes. There is also a need to evaluate whether myosteatosis influences the incidence of type 2 diabetes independent of overall adiposity. A better understanding of the factors that regulate myosteatosis may lead to the development of novel therapies that influence a more metabolically 'healthy' skeletal muscle.

Characterization of distinct mesenchymal-like cell populations from human skeletal muscle in situ and in vitro

Human skeletal muscle is an essential source of various cellular progenitors with potential therapeutic perspectives. We first used extracellular markers to identify in situ the main cell types located in a satellite position or in the endomysium of the skeletal muscle. Immunohistology revealed labeling of cells by markers of mesenchymal (CD13, CD29, CD44, CD47, CD49, CD62, CD73, CD90, CD105, CD146, and CD15 in this study), myogenic (CD56), angiogenic (CD31, CD34, CD106, CD146), hematopoietic (CD10, CD15, CD34) lineages. We then analysed cell phenotypes and fates in short- and long-term cultures of dissociated muscle biopsies in a proliferation medium favouring the expansion of myogenic cells. While CD56(+) cells grew rapidly, a population of CD15(+) cells emerged, partly from CD56(+) cells, and became individualized. Both populations expressed mesenchymal markers similar to that harboured by human bone marrow-derived mesenchymal stem cells. In differentiation media, both CD56(+) and CD15(+) cells shared osteogenic and chondrogenic abilities, while CD56(+) cells presented a myogenic capacity and CD15(+) cells presented an adipogenic capacity. An important proportion of cells expressed the CD34 antigen in situ and immediately after muscle dissociation. However, CD34 antigen did not persist in culture and this initial population gave rise to adipogenic cells. These results underline the diversity of human muscle cells, and the shared or restricted commitment abilities of the main lineages under defined conditions.

New source of muscle-derived stem cells with potential for alveolar bone reconstruction in cleft lip and/or palate patients

Cleft lip and palate (CLP), one of the most frequent congenital malformations, affects the alveolar bone in the great majority of the cases, and the reconstruction of this defect still represents a challenge in the rehabilitation of these patients. One of the current most promising strategy to achieve this goal is the use of bone marrow stem cells (BMSC); however, isolation of BMSC or iliac bone, which is still the mostly used graft in the surgical repair of these patients, confers site morbidity to the donor. Therefore, in order to identify a new alternative source of stem cells with osteogenic potential without conferring morbidity to the donor, we have used orbicular oris muscle (OOM) fragments, which are regularly discarded during surgery repair (cheiloplasty) of CLP patients. We obtained cells from OOM fragments of four unrelated CLP patients (CLPMDSC) using previously described preplating technique. These cells, through flow cytometry analysis, were mainly positively marked for five mesenchymal stem cell antigens (CD29, CD90, CD105, SH3, and SH4), while negative for hematopoietic cell markers, CD14, CD34, CD45, and CD117, and for endothelial cell marker, CD31. After induction under appropriate cell culture conditions, these cells were capable to undergo chondrogenic, adipogenic, osteogenic, and skeletal muscle cell differentiation, as evidenced by immunohistochemistry. We also demonstrated that these cells together with a collagen membrane lead to bone tissue reconstruction in a critical-size cranial defects previously induced in nonimmunocompromised rats. The presence of human DNA in the new bone was confirmed by PCR with human-specific primers and immunohistochemistry with human nuclei antibodies. In conclusion, we showed that cells from OOM have phenotypic and behavior characteristics similar to other adult stem cells, both in vitro and in vivo. Our findings suggest that these cells represent a promising source of stem cells for alveolar bone grafting treatment, particularly in young CLP patients.

Longitudinal study of muscle strength, quality, and adipose tissue infiltration

BACKGROUND

Sarcopenia is thought to be accompanied by increased muscle fat infiltration. However, no longitudinal studies have examined concomitant changes in muscle mass, strength, or fat infiltration in older adults.

OBJECTIVE

We present longitudinal data on age-related changes in leg composition, strength, and muscle quality (MQ) in ambulatory, well-functioning men and women. We hypothesized that muscle cross-sectional area (CSA) and strength would decrease and muscular fat infiltration would increase over 5 y.

DESIGN

Midthigh muscle, subcutaneous fat (SF), and intermuscular fat (IMF) CSAs and isokinetic leg muscle torque (MT) and MQ (MT/quadriceps CSA) were examined over 5 y in the Health, Aging, and Body Composition study cohort (n = 1678).

RESULTS

Men experienced a 16.1% loss of MT, whereas women experienced a 13.4% loss. Adjusted annualized decreases in MT were 2-5 times greater than the loss of muscle CSA in those who lost weight and in those who remained weight-stable. Weight gain did not prevent the loss of MT, despite a small increase in muscle CSA. Only those who gained weight had an increase in SF (P < 0.001), whereas those who lost weight also lost SF (P < 0.001). There was an age-related increase in IMF in men and women (P < 0.001), and IMF increased in those who lost weight, gained weight, or remained weight-stable (all P < 0.001).

CONCLUSIONS

Loss of leg MT in older adults is greater than muscle CSA loss, which suggests a decrease in MQ. Additionally, aging is associated with an increase in IMF regardless of changes in weight or SF.

Multi-potent differentiation of human purified muscle-derived cells: potential for tissue regeneration

OBJECTIVE

To investigate whether CD34+ purified human muscle-derived cells (hMDCs) are capable of multiple lineage differentiation.

MATERIALS AND METHODS

The hMDCs were isolated from human skeletal muscle and purified using a CD34+ cell selection system (Dynal Biotech, Oslo, Norway). Adherent populations of cells were expanded in culture and cell differentiation was induced using different kinds of growth factors and different differentiation-conditional media. The immunohistochemical properties of CD34+ hMDCs were examined after varying periods in culture. Reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting were used to investigate the gene expression of the undifferentiated and differentiated hMDCs.

RESULTS

Using special differentiation conditions the CD34+ hMDCs could be differentiated into myogenic cells, adipocytes, osteocytes and chondrocytes. The differentiation was confirmed by immunohistochemistry. RT-PCR and Western blotting showed multiple-lineage gene-level expression in the different cultivation periods of the differentiated cells.

CONCLUSIONS

We confirmed the multi-lineage capacity of a population of stem cells, termed CD34+ hMDCs. Our findings showed that CD34+ hMDCs are capable of multiple mesodermal-lineage differentiation, as shown by the expression of several lineage-specific genes. They can be differentiated toward the myogenic, osteogenic, adipogenic and chondrogenic lineages. These cells might have potential for use in tissue regeneration.

Muscle precursor cells isolated from aged rats exhibit an increased tumor necrosis factor- alpha response

Improving muscle precursor cell (MPC, muscle-specific stem cells) function during aging has been implicated as a key therapeutic target for improving age-related skeletal muscle loss. MPC dysfunction during aging can be attributed to both the aging MPC population and the changing environment in skeletal muscle. Previous reports have identified elevated levels of tumor necrosis factor- alpha (TNF- alpha ) in aging, both circulating and locally in skeletal muscle. The purpose of the present study was to determine if age-related differences exist between TNF- alpha -induced nuclear factor-kappa B (NF- kappaB) activation and expression of apoptotic gene targets. MPCs isolated from 32-month-old animals exhibited an increased NF- kappaB activation in response to 1, 5, and 20 ng mL(-1) TNF- alpha, compared to MPCs isolated from 3-month-old animals. No age differences were observed in the rapid canonical signaling events leading to NF- kappaB activation or in the increase in mRNA levels for TNF receptor 1, TNF receptor 2, TNF receptorassociated factor 2 (TRAF2), or Fas (CD95) observed after 2 h of TNF- alpha stimulation. Interestingly, mRNA levels for TRAF2 and the cell death-inducing receptor, Fas (CD95), were persistently upregulated in response to 24 h TNF- alpha treatment in MPCs isolated from 32-month-old animals, compared to 3-month-old animals. Our data indicate that age-related differences may exist in the regulatory mechanisms responsible for NF- kappaB inactivation, which may have an effect on TNF- alpha-induced apoptotic signaling. These findings improve our understanding of the interaction between aged MPCs and the changing environment associated with age, which is critical for the development of potential clinical interventions aimed at improving MPC function with age.

Alpha v beta 3 and alpha v beta 5 integrins and their role in muscle precursor cell adhesion

BACKGROUND INFORMATION

Functional adaptation of skeletal muscle is a requirement for different muscle groups (e.g. craniofacial, ocular and limb) to undergo site-specific changes. Such tissue remodelling depends on dynamic interactions between muscle cells and their extracellular matrix, via participation of multifunctional molecules such as integrins. In view of data suggesting a role in fundamental muscle biology and muscle development in other systems, the present study has focused on expression and function of alpha v integrins, in cultured adult human craniofacial muscle (masseter) precursor cells and myotubes, and the predominantly fibroblastic IC (interstitial cells) population.

RESULTS AND CONCLUSIONS

Flow-cytometric phenotyping and immunofluorescence phenotyping show that alpha v, alpha v beta 3 and alpha v beta 5 are expressed in all mononuclear cells (muscle precursors and IC) seeded on muscle extracellular molecules such as gelatin, VN (vitronectin) and FN (fibronectin). In this system, blockade of alpha v activity using a function-perturbing antibody abrogates cell migration on VN and FN. alpha v integrins act predominantly as VN receptors as cell-substrate attachment is diminished when alpha v neutralizing agents are introduced into cultures seeded on VN, and this inhibition is reversible; these integrins also appear to be minor FN receptors. These results demonstrate that the alpha v subset of integrins present on both myogenic precursors and IC is an essential cohort of VN and, to a lesser extent, FN receptors mediating cell adhesion and, either directly or indirectly, arbiters of cell motility.

Activating muscle stem cells: therapeutic potential in muscle diseases

PURPOSE OF REVIEW

The satellite cell is the principal muscle stem cell. Recent research, however, has highlighted new stem cell sources that, once activated in the muscle tissue, can participate in muscle regeneration. This article reviews the state of research on stem cell populations that have potential for treatment of muscular dystrophies.

RECENT FINDINGS

Despite recent findings about the stem cell character of satellite cells and their in-vivo myogenic potential, limitations related to muscle precursor cell transfer therapy have encouraged the investigation of stem cell sources other than satellite cells. Current research is focused on identifying the best stem cell in the endothelial compartment, which is able to be systemically delivered to reach all the muscles and to contribute to widespread muscle regeneration within these muscles.

SUMMARY

Current results highlight many possible stem cell sources for stem cell therapy of muscle diseases, and work is ongoing to identify the most effective candidate that is able to robustly regenerate muscle tissue and to functionally repopulate the muscle stem cell compartment.