*2.1. Cell Isolation*

Skin and muscle specimens were obtained from 3 healthy donors, aged between 20 and 40, upon informed consent in line with the Declaration of Helsinki. Tissues were digested and muscular cell suspension was cultured in alpha Minimum Essential Medium (αMEM; Thermo Fisher Scientific, Waltham, MA, USA), 20% fetal bovine serum (FBS; Thermo Fisher Scientific), and penicillin (100 U/mL; Thermo Fisher Scientific) and streptomycin (100 μg/mL; Thermo Fisher Scientific). Pericytes were then selected by their ability to grow on plastic at low confluence (0.1–1 <sup>×</sup> 104 cell/cm2). Skin cells were plated in Dulbecco's Modified Eagle Medium (DMEM; Thermo Fisher Scientific) supplemented with 10% FBS, 0.5 mM β-mercaptoethanol (Thermo Fisher Scientific), 100 U/mL penicillin, and 100 μg/mL streptomycin (Thermo Fisher Scientific) at a density of 5 <sup>×</sup> 104 cells/cm2.

#### *2.2. Tube-Formation Assay*

Pericytes and human umbilical vein endothelial cells (HUVEC; Lonza, Basel, Switzerland) were seeded in 8-well Permanox chamber slides coated with Matrigel (Becton Dickinson Franklin Lakes, NJ, USA), either separately (3.75 <sup>×</sup> <sup>10</sup><sup>4</sup> cells per well) or co-cultured together at a 1:4 ratio, in Endothelial Cell Growth Basal Medium-2 (EBM-2; Lonza). Cells were incubated for 5 h to allow tube formation. Images of newly formed networks were captured at 10X magnification.

All experiments were performed in duplicates. Analysis was achieved using the Angiogenesis Analyzer tool (ImageJ Software, https://imagej.nih.gov/ij/).
