Mesenchymal stem/stromal cells (MSCs) are promising cell sources for regenerative therapies due to their multipotency and ready availability, but their application can be complicated by patient-specific factors like age or illness. MSCs have been investigated for the treatment of many musculoskeletal disorders, including osteoarthritis and osteoporosis. Due to the prevalence of these diseases in older populations, researchers have studied how aging affects MSC properties and have found that proliferation and differentiation potential are impaired. However, these effects have never been compared among MSCs isolated from multiple tissue sources in the same, healthy donor. Revealing differences in how MSCs are affected by age could help identify an optimal cell source for musculoskeletal therapies targeting older patients. MSCs were isolated from young and old rabbit bone marrow, muscle, and adipose tissue. Cell yield and viability were quantified after isolation procedures, and expansion properties were assessed using assays for proliferation, senescence, and colony formation. Multipotency was also examined using lineage-specific stains and spectrophotometry of metabolites. Results were compared between age groups and among MSC sources. Results showed that MSCs are differentially influenced by aging, with bone marrow-derived stem cells having impaired proliferation, senescence, and chondrogenic response, whereas muscle-derived stem cells and adipose-derived stem cells exhibited no negative effects. While age reduced overall cell yield and adipogenic potential of all MSC populations, osteogenesis and clonogenicity remained unchanged. These findings indicate the importance of age as a factor when designing cell-based therapies for older patients.

The mechanical properties of adipose-derived stem cell (ASC) clones correlate with their ability to produce tissue-specific metabolites, a finding that has dramatic implications for cell-based regenerative therapies. Autologous ASCs are an attractive cell source due to their immunogenicity and multipotent characteristics. However, for practical applications ASCs must first be purified from other cell types, a critical step which has proven difficult using surface-marker approaches. Alternative enrichment strategies identifying broad categories of tissue-specific cells are necessary for translational applications. One possibility developed in our lab uses single-cell mechanical properties as predictive biomarkers of ASC clonal differentiation capability. Elastic and viscoelastic properties of undifferentiated ASCs were tested via atomic force microscopy and correlated with lineage-specific metabolite production. Cell sorting simulations based on these "mechanical biomarkers" indicated they were predictive of differentiation capability and could be used to enrich for tissue-specific cells, which if implemented could dramatically improve the quality of regenerated tissues.cell mechanics | mesenchymal stem cell enrichment | viscoelasticity | single-cell characterization | AFM A dipose tissue contains a heterogeneous population of mesenchymal stem cells (MSCs) known as adipose-derived stem cells (ASCs) (1). ASCs are capable of differentiating into a variety of lineage-specific cell types, including adipocytes, osteoblasts, and chondrocytes (1-3). In comparison to MSCs derived from other tissues, ASCs are simple to isolate and available in large quantities (4, 5). Because of the cells' mesodermal origin, ASCs have been used for many soft tissue and orthopaedic applications (6-10). Unfortunately, ASC isolation is confounded by the lack of distinct and universally effective MSC biomarkers. Adipose tissue contains multiple cell types, including mature adipocytes, fibroblasts, smooth muscle cells, and endothelial cells (11), which can contaminate the stromal fraction collected during ASC isolation. While conventional methods such as flow cytometry can isolate stem cells using surface antigen expression (1, 2, 12), resulting cell yields are often less than 1% (13,14). Furthermore, the surface antigens present on ASCs can also be found on other cell types in adipose tissue, complicating the isolation of pure mesenchymal stem cell populations (15-17). Collectively, these limitations suggest a need for alternative biomarkers that allow for ASC enrichment based on lineage potential.Recently, single-cell mechanical properties were found to be akin to gene and protein expressions, capable of distinguishing differences in cellular subpopulations, disease state, and tissue source (18)(19)(20)(21)(22). Cells display varying levels of resistance to deformation (elasticity) and flow (viscosity) in response to an applied force. This behavior depends on the composition and organization of subcellular structures, particularly the cytosk...

The Pax6 gene has attracted intense research interest due to its apparently important role in the development of eyes and the central nervous system (CNS) in many animal groups. Pax6 is also of interest for comparative genomics since it has not been duplicated in tetrapods, making for a direct orthology between the Ciona intestinalis gene CiPax6 and Pax6 in mammals. CiPax6 has been shown to be expressed in the anterior brain, caudal nerve cord, and in parts of the brain associated with the photoreceptive ocellus. This information was extended here using in-situ hybridization, and shows that CiPax6 transcripts mark the lateral regions of the nerve cord, remarkably similar to Pax6 expression in the mouse. As a means of dissecting the cis-regulation of CiPax6 we tested 8 kb of sequence using transient reporter transgene assays. Three separate regions were found that work together to drive the overall CiPax6 expression pattern. A 211 bp sequence 2 kb upstream of the first exon was found to be a major enhancer driving expression in the sensory vesicle (the anterior portion of the ascidian brain). Other upstream sequences were shown to work with the sensory vesicle enhancer to drive expression in the remainder of the CNS. An "eye enhancer" was localized to the first intron, which controls specific expression in the central portion of the sensory vesicle, including photoreceptor cells. The fourth intron was found to repress ectopic expression of the reporter gene in middle portions of the embryonic brain. Aspects of this overall regulatory organization are similar to the organization of the Pax6 homologs in mice and Drosophila, particularly the presence of intronic elements driving expression in the eye, brain and nerve cord.

These findings suggest that lamin C protein expression is strongly associated with whole-cell mechanical properties and could potentially serve as a biomarker for mechanophenotype.