PTEN in somatostatin-positive stromal progenitors modulates fibrotic stress and is required for inhibitory gap-junction coupling within the limb blastema
June 29
Introduction: The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a negative regulator of the mTOR cascade and is strongly associated with congenital overgrowth syndromes, with up to 25 % of macrodactyly patients harboring PTEN mutations. Mice with germline PTEN haploinsufficiency display tissue hypertrophy and scarring, as do several conditional PTEN knockout models restricted to mesenchymal lineages. Analyses of human biopsy material and diverse genetic mouse models suggest that malfunction of inhibitory stromal subpopulations may contribute to maladaptive repair, yet the underlying mechanisms remain unclear. PTEN is an ideal entry point because it governs the development of mesenchymal progenitors originating from lateral plate mesoderm, favoring the survival and maturation of Runx2⁺ osteo-lineage cells at the expense of somatostatin (SST)⁺ stromal cells.
Methods: Here, we examined how PTEN regulates SST⁺ cells at both cellular and circuit levels within the inner zone of the limb blastema (IZB), a compartment that determines key regenerative outcomes such as scar burden and tissue integration. Adult mice bearing a floxed Pten allele were crossed with Sst-CreERT2 drivers, and recombination was induced post-amputation. Scar formation was quantified histologically; bioelectric properties were assessed by voltage-sensitive dye imaging; and local cell-to-cell connectivity was mapped with high-resolution photolytic uncaging of caged gap-junction tracers.
Results: Ablating PTEN in SST⁺ stromal cells heightened fibrotic stress and reduced local gap-junction coupling across the IZB. Specifically, the intervention diminished junctional conductance between individual cells and redistributed inhibitory contacts in a lineage-specific manner. In striking contrast to the deficit in intrinsic inhibitory connectivity, excitatory trophic input from the principal extrinsic driver—the regenerating peripheral nerve—was potentiated, leading to elevated calcium transients in blastemal cells. These findings position PTEN as a pivotal regulator of the balance between extrinsic pro-growth cues and intrinsic inhibitory networks during appendage regeneration.