In-Vitro Studies of Aging

Cell therapy in tendon disorders: what is the current evidence?

BACKGROUND

Various types of tissue-derived cells are being experimented with for the treatment of tendinopathy, tendon repair, and use in tissue engineering.

PURPOSE

The aim of this systematic review is to explore the current evidence with a view to evaluate the potential of this therapeutic intervention.

STUDY DESIGN

Systematic review.

METHODS

A review of the literature was conducted using PubMed. Search criteria included keywords "tendinopathy," "tendinitis," "tendinosis," "epicondylitis," "stem cell," and "cell therapy." Articles not written in English language were excluded.

RESULTS

A total number of 379 articles were identified and a critical appraisal of the relevant articles was undertaken, which encompassed human and animal research. The review included articles related to various tissue-derived cells such as tendon progenitors, adipose tissue, synovium, muscle, bone marrow, and skin. The utility of cell therapy in tissue engineering and rotator cuff repair was also assessed.

CONCLUSION

With the limitation of the available evidence, the literature suggests that cell therapy is applicable and may be effective for the treatment of tendinopathy. However, further research into the precise biological mechanisms, long-term implications, and cost-effectiveness is needed.

Effects of age on the repair ability of mesenchymal stem cells in rabbit tendon

Successful tissue engineered repair in the aging adult requires an abundant source of autologous, multipotent mesenchymal stem cells (MSCs). Although the number of bone marrow-derived MSCs declines dramatically with aging, their effectiveness in repair with increasing age has not been studied. We tested the hypothesis that MSCs harvested from geriatric rabbits would not repair patellar tendon defects as well as MSCs harvested from younger adult rabbits. In a novel within-subjects experiment, autologous MSCs were isolated from 1-year old rabbits, culture expanded, and cryogenically preserved. After housing the rabbits for 3 years, MSCs were re-harvested from the 4-year old rabbits and expanded. Five hundred thousand thawed and fresh MSCs were each separately mixed with type I collagen gel (333.3 x 10(3) cells/mg collagen) 24 h before surgery, and the resulting constructs implanted in bilateral full-length central third tendon defects. Twelve weeks post-surgery, the bone-tendon repair-bone units were failed in tension. Intra-animal (paired) comparisons between repair tissue treated with 1-year old MSCs and repair tissue treated with 4-year old MSCs resulted in no significant differences (alpha=0.05) in material properties including maximum stress (10.8 MPa vs. 9.9 MPa; p=0.762), modulus (139.8 MPa vs. 146.2 MPa; p=0.914), and strain energy density (0.52 N mm/mm(3) vs. 0.53 N mm/mm(3); p=0.966). Despite an age-related trend, there were also no significant differences in structural properties including maximum force (62.9 N vs. 27.0 N; p=0.070), stiffness (24.9 N/mm vs. 12.0 N/mm; p=0.111), and strain energy (87.2 N mm vs. 31.4 N mm; p=0.061). A subset of the rabbits (n=4 1 yrMSC, n=2 4 yrMSC) showed the presence of ectopic bone in the repair region and were not included in the mechanical analyses. We conclude that in the rabbit model MSCs do not lose their benefit as a tendon repair therapy with aging and that MSCs can be cryogenically stored for 3 years and still effectively repair soft tissue injuries.

TGF-beta 1 gene expression in cultured human keratinocytes does not decrease with biologic age

The biologic activity of cultured epithelial grafts is believed to diminish with increasing cellular age. Therefore, keratinocytes from young donors are used preferentially in the production of cultured allografts for wound treatment. However, the impact of biologic age on cytokine gene expression by human keratinocytes has not been previously investigated. In this study, transforming growth factor-beta 1 (TGF-beta 1) gene expression in human keratinocytes derived from normal foreskins of males ranging in age from 7 months to 82 years was analyzed. Keratinocytes were harvested from fresh specimens and cultivated in vitro on 3T3 fibroblast feeder layers through second passage. The cells were analyzed both qualitatively and semiquantitatively for TGF-beta 1 gene expression using three separate techniques: in situ hybridization, Northern hybridization, and competitive polymerase chain reaction. By in situ hybridization, the signal representing TGF-beta 1 transcript was detected in cells in all layers of the stratified cultures, and immunohistochemical staining for TGF-beta 1 protein was equally intense in all layers. Northern blots of total RNA extracted from the cultivated cells showed no decrease in band density with increasing biologic age. Likewise, no decrease in TGF-beta 1 mRNA levels with biologic age was observed using a semiquantitative polymerase chain reaction assay. These results indicate that the potential for TGF-beta 1 gene expression in cultured foreskin keratinocytes does not decline with increasing cellular age. The findings imply that the clinical performance of cultured grafts, at least as it relates to the elaboration of this growth factor, may not be significantly altered by the biologic age of the keratinocyte donor.

Evidence for accelerated skin wrinkling among developmentally delayed individuals with Down's syndrome

Down's Syndrome (DS) is a genetic disorder involving mental retardation which is reported to be a condition of accelerated aging. However, few studies exist which examine age-dependent changes in DS and these studies fail to include a control group. In the present study a non-invasive, painless, and easily obtainable measure reflecting age-dependent topographical changes of the skin (skin wrinkling) was obtained in 15 DS subjects, 14 developmentally disabled (DD) (mentally retarded) controls (DD controls) and 16 healthy controls of similar ages ranging from 22 to 51 years. The healthy control group failed to show correlations of skin measures with age, as predicted for the age-range of these subjects, based on results of previous studies. However, the DS group showed significant correlations of all skin measures from relatively non-sun-exposed and sun-exposed skin sites, with age. The DD control also showed significant correlations with age of several but not all skin sites and the correlation coefficients tended to be less than that of the DS; at least, when contrasted with the healthy controls the DS showed greater values of several skin measures suggestive of accelerated skin wrinkling. These results provide evidence for accelerated aging of the skin, and possibly greater effects of sun-exposure on skin wrinkling, in DS and possibly (DD) individuals in contrast to healthy individuals without a genetic disorder and without mental retardation.

Low-molecular-weight peptides in bone extracts that stimulate osteoblast mitogenesis

Although a majority of regulatory peptides elaborated by neuroendocrine cells are small, i.e., less than 50-60 residues, no low-molecular-weight, bone-derived mitogenic peptides have been described. We have size-fractionated extracts of neonatal mouse calvaria, a rapidly forming bone, and assayed for osteoblast proliferation. Mitogenic peptides with estimated sizes of 1,600, 1,050, and 770 daltons were detected. Their protein nature was demonstrated by the reduction in mitogenic activity following protease treatment. Fibroblast mitogenesis was not stimulated by any of the peptides. These data indicate that there are mitogenic peptides in bone smaller than any previously described locally-derived bone cell growth factor.