Tsc2 deletion in mesenchymal cells improves distal digit regeneration

Summary: Abstract Body: Digit regeneration is limited in mammals. After distal amputation, undifferentiated blastema cells may drive complete regeneration or pro-inflammatory cells may induce a fibrotic, non-regenerative scar. We hypothesized that deletion of Tsc2 in mesenchymal cells would support nail regeneration after amputation, based on our previous work showing that loss of this gene altered skin morphogenesis and regeneration. Tsc2 conditional knockout (cKO) mice were generated from a cross between mice with a conditional Tsc2 allele and mice containing the cre recombinase transgene possessing a Prrx1 enhancer, deleting Tsc2 on both alleles in limb bud mesenchyme. The middle three hindpaw digits from 11 control and 10 Tsc2 cKO mice were amputated by cutting through the most distal phalanx (P3). Digit tip regeneration was scored visually as complete, partial, or none. At 28 days after amputation, digits were harvested and histological sections were analyzed to quantify P3 bone length and percent regeneration. From visual inspection, 54 of 60 digits in the cKO group showed complete regeneration indicating full digit elongation and nail regrowth compared to 11 out of 62 digits in the control group (p < 0.005). P3 bone length measured in amputated digits from the cKO group was 690 ± 290 µm, significantly greater than 430 ± 260 µm in the control group (p < 0.005). In summary, our data demonstrates Tsc2 deletion in mesenchymal cells within a mouse model improves bone digit regeneration and regeneration of the nail. Understanding signaling pathways relevant to Tsc2 deletion in mesenchymal cells can open new avenues to improve digit regeneration after amputation. Donald Aduba^{1, 2}, Samantha Verling³, Sandhya Xavier^{1, 2}, Ernest Phillips^{1, 2}, Peter Klover^{1, 2}, Neera Nathan^{1, 2}, Ji-an Wang^{1, 2}, Shaowei Li^{1, 2}, Rajesh Thangapazham^{1, 2}, Leonard Sperling¹, Joel Moss³, Thomas Darling¹ 1. Dermatology, Uniformed Services University of the Health Sciences, Bethesda, MD, United States. 2. Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc., Bethesda, MD, United States. 3. Critical Care Medicine and Pulmonary Branch, NHLBI, National Institutes of Health, Bethesda, MD, United States. Stem Cell Biology, Tissue Regeneration and Wound Healing