Progerin phosphorylation in interphase is lower and less mechanosensitive than lamin-A，C in iPS-derived mesenchymal stem cells.

Interphase phosphorylation of lamin-A，C depends dynamically on a cell's microenvironment， including the stiffness of extracellular matrix. However， phosphorylation dynamics is poorly understood for diseased forms such as progerin， a permanently farnesylated mutant of LMNA that accelerates aging of stiff and mechanically stressed tissues. Here， fine-excision alignment mass spectrometry (FEA-MS) is developed to quantify progerin and its phosphorylation levels in patient iPS cells differentiated to mesenchymal stem cells (MSCs). The stoichiometry of total A-type lamins (including progerin) versus B-type lamins measured for Progeria iPS-MSCs prove similar to that of normal MSCs， with total A-type lamins more abundant than B-type lamins. However， progerin behaves more like farnesylated B-type lamins in mechanically-induced segregation from nuclear blebs. Phosphorylation of progerin at multiple sites in iPS-MSCs cultured on rigid plastic is also lower than that of normal lamin-A and C. Reduction of nuclear tension upon i) cell rounding/detachment from plastic， ii) culture on soft gels， and iii) inhibition of actomyosin stress increases phosphorylation and degradation of lamin-C > lamin-A > progerin. Such mechano-sensitivity diminishes， however， with passage as progerin and DNA damage accumulate. Lastly， transcription-regulating retinoids exert equal effects on both diseased and normal A-type lamins， suggesting a differential mechano-responsiveness might best explain the stiff tissue defects in Progeria.