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.

SIRPA-Inhibited, Marrow-Derived Macrophages Engorge, Accumulate, and Differentiate in Antibody-Targeted Regression of Solid Tumors.

Marrow-derived macrophages are highly phagocytic, but whether they can also traffic into solid tumors and engulf cancer cells is questionable, given the well-known limitations of tumor-associated macrophages (TAMs). Here, SIRPα on macrophages from mouse and human marrow was inhibited to block recognition of its ligand, the "marker of self" CD47 on all other cells. These macrophages were then systemically injected into mice with fluorescent human tumors that had been antibody targeted. Within days, the tumors regressed, and single-cell fluorescence analyses showed that the more the macrophages engulfed, the more they accumulated within regressing tumors. Human-marrow-derived macrophages engorged on the human tumors, while TAMs were minimally phagocytic, even toward CD47-knockdown tumors. Past studies had opsonized tumors in situ with antibody and/or relied on mouse TAMs but had not injected SIRPα-inhibited cells; also, unlike past injections of anti-CD47, blood parameters remained normal and safe. Consistent with tumor-selective engorge-and-accumulate processes in vivo, phagocytosis in vitro inhibited macrophage migration through micropores that mimic features of dense 3D tissue. Accumulation of SIRPα-inhibited macrophages in tumors favored tumor regression for 1-2 weeks, but donor macrophages quickly differentiated toward non-phagocytic, high-SIRPα TAMs. Analyses of macrophages on soft (like marrow) or stiff (like solid tumors) collagenous gels demonstrated a stiffness-driven, retinoic-acid-modulated upregulation of SIRPα and the mechanosensitive nuclear marker lamin-A. Mechanosensitive differentiation was similarly evident in vivo and likely limited the anti-tumor effects, as confirmed by re-initiation of tumor regression by fresh injections of SIRPα-inhibited macrophages. Macrophage motility, phagocytosis, and differentiation in vivo are thus coupled.

DNA Damage Follows Repair Factor Depletion and Portends Genome Variation in Cancer Cells after Pore Migration.

Migration through micron-size constrictions has been seen to rupture the nucleus, release nuclear-localized GFP, and cause localized accumulations of ectopic 53BP1-a DNA repair protein. Here, constricted migration of two human cancer cell types and primary mesenchymal stem cells (MSCs) increases DNA breaks throughout the nucleoplasm as assessed by endogenous damage markers and by electrophoretic "comet" measurements. Migration also causes multiple DNA repair proteins to segregate away from DNA, with cytoplasmic mis-localization sustained for many hours as is relevant to delayed repair. Partial knockdown of repair factors that also regulate chromosome copy numbers is seen to increase DNA breaks in U2OS osteosarcoma cells without affecting migration and with nucleoplasmic patterns of damage similar to constricted migration. Such depletion also causes aberrant levels of DNA. Migration-induced nuclear damage is nonetheless reversible for wild-type and sub-cloned U2OS cells, except for lasting genomic differences between stable clones as revealed by DNA arrays and sequencing. Gains and losses of hundreds of megabases in many chromosomes are typical of the changes and heterogeneity in bone cancer. Phenotypic differences that arise from constricted migration of U2OS clones are further illustrated by a clone with a highly elongated and stable MSC-like shape that depends on microtubule assembly downstream of the transcription factor GATA4. Such changes are consistent with reversion to a more stem-like state upstream of cancerous osteoblastic cells. Migration-induced genomic instability can thus associate with heritable changes.

Efficient nuclear delivery and nuclear body localization of antisense oligo-nucleotides using degradable polymersomes.

Delivery of antisense oligonucleotides, AON, presents many of the same challenges as delivery of any nucleic acid: charge, stability, cell uptake, endolysosomal escape, and entry into the nucleus. Here we demonstrate efficient delivery of AON after loading into biodegradable polymer vesicles or 'polymersomes'. We focus on AON delivery to muscle cells in vitro and in vivo because of the emergence of AON in therapeutic strategies directed at muscular dystrophies. To first clarify uptake kinetics without the complications of typical multi-layered myotube cultures, we use micro-patterned C2C12 cells and show efficient uptake of AON-polymersomes. The biodegradable polymersomes break down and foster AON escape with the binding of fluorescent-AON into the nuclear bodies. Intramuscular injections of the polymersome-AON into the hind limbs of mdx-dystrophic mice show more efficient nuclear uptake than AON alone and also lead to dystrophin expression in the mdx mice. In sum, these neutral, degradable carriers of AON show promise in vivo.