Survival-associated cellular response maintained in pancreatic ductal adenocarcinoma (PDAC) switched between soft and stiff 3D microgel culture

Pancreatic ductal adenocarcinoma (PDAC) accounts for about 90% of all
pancreatic cancer cases. Five-year survival rates have remained below 12%
since the 1970s, in part due to the difficulty in detection before
metastasis (migration and invasion into neighboring organs and glands).
Mechanical memory is a concept that has emerged over the past decade that
may provide a path towards understanding how invading PDAC cells
“remember” the mechanical properties of their diseased (“stiff,” elastic
modulus, E ≈ 10 kPa) microenvironment even whilst invading a healthy
(“soft,” E ≈ 1 kPa) microenvironment. Here, we investigated the role of
mechanical priming by culturing a dilute suspension of PDAC (FG) cells
within a 3D, rheologically tunable microgel platform from hydrogels with
tunable mechanical properties. We conducted a suite of acute (short-term)
priming studies where we cultured PDAC cells in either a soft (E ≈ 1 kPa)
or stiff (E ≈ 10 kPa) environment for 6 h, then removed and placed them
into a new soft or stiff 3D environment for another 18 h. Following these
steps, we conducted RNA-seq analyses to quantify gene expression. Initial
priming in 3D culture showed persistent gene expression for the duration
of the study, regardless of the subsequent environments (stiff or soft).
Stiff 3D culture was associated with the down-regulation of tumor
suppressors (LATS1, BCAR3, CDKN2C ), as well as the up-regulation of
cancer-associated genes (RAC3). Immunofluorescence staining (BCAR3, RAC3)
further supported the persistence of this cellular response, with BCAR3
upregulated in soft culture, and RAC3 upregulated in stiff-primed culture.
Stiff-primed genes were stratified against patient data found in The
Cancer Genome Atlas (TCGA). Upregulated genes in stiff-primed 3D culture
were associated with decreased survival in patient data, suggesting a link
between patient survival and mechanical priming.