The intersection of gene expression and mechanical phenotype
Eric M. Darling, Ph.D.1, Nicholas R. Labriola1, Rafael D. González-Cruz, M.Eng.1, Manisha
Kanthilal, Sc.M.1, Jessica S. Sadick1, Vera C. Fonseca, M.S.1
1Brown
University, Providence, RI
Gene expression is a ubiquitous means to characterize cell phenotype, and more recently,
single-cell mechanical properties have been used to describe disease, dysfunction, and
differentiation potential. The objective of this multi-part project was to investigate the intersection
of live-cell gene expression and cellular mechanical properties. In project #1, mesenchymal
stem cells were adipogenically differentiated and assessed for mechanical changes over time.
Molecular beacons targeting adipogenic mRNA (PPARG) identified differentiating and nondifferentiating cells in heterogeneous cultures. Results showed that single-cell mechanical
properties did not change temporally. However, PPARG+ cells were more compliant than
PPARG- cells, regardless of media environment. The percentage of PPARG+ cells in
adipogenic cultures increased over time, accounting for a perceived decrease in average
mechanical properties. These findings highlight a common problem with heterogeneous
populations, namely that the average response is attributed to all cells when only a subset may
be responsible. Project #2 delved further into the connection between gene expression and
cellular mechanical properties based on recent work showing that microtissue stiffness
correlates with nuclear protein content. Multiple cell types, ranging in cell stiffness from 0.3-1.3
kPa, were assessed for nuclear lamin mRNA (LMNA) by qPCR. A positive correlation existed
between cellular elastic modulus and LMNA, which suggests that LMNA expression could serve
as a potential proxy for cellular mechanical properties. In combination with fluorescence-based
molecular beacons, these approaches may provide a means to discriminate cells by mechanical
phenotype for both diagnostic and regenerative medicine applications.