PYY regulates human skeletal muscle progenitor cell proliferation
Authors: Gheller Brandon JF , Roman Heather A , Thalacker‐Mercer Anna E 
Published: November 2023

Adult skeletal muscle stem cells (satellite cells) are required for regeneration after injury. The regulation of regeneration has not been fully elucidated, but relies on factors both intrinsic and extrinsic to the satellite cells. Identifying and characterizing factors that influence satellite cell proliferation is necessary for the development of therapies to aid with muscle‐related disorders. We have recently shown that peptide YY (PYY) is temporally expressed and likely synthesized in differentiating muscle progenitor cells (MPCs). The function(s) of intrinsic or extrinsic PYY in MPCs is currently unknown. PYY is a ligand for the Y receptors. Activation of the Y receptors has been shown to allow stem cells to remain in a proliferative state even in the absence of fibroblast growth factor (FGF), a critical proliferative regulator.

Objective

Our objectives were 1) to determine the PYY protein levels over time in proliferating MPCs, and 2) to evaluate the effect of exogenous PYY on human MPC proliferation in the presence and absence of FGF.

Methods

Human MPCs were obtained from 4 young female donors via vastus lateralis muscle biopsies. MPCs were sorted to produce a homogenous culture. MPCs were maintained in the proliferative state in a growth media (GM) containing Ham's F12, 20% fetal bovine serum, and 5 ng/mL bFGF. Study 1: MPCs were grown in GM. PYY protein levels were measured by an In‐Cell Western™ assay on days 5, 6, and 7 of proliferation. Study 2: Three days after seeding MPCs in GM, cultures were switched to one of four media: 1) GM with 5 ng/mL bFGF (CON); 2) GM without bFGF (noFGF); 3) GM with a physiologically relevant dose of PYY (500 pM) but without bFGF (Norm‐PYY); 4) GM with a supra‐physiological dose of PYY (1 nM) but without bFGF (High‐PYY) and grown for an additional 4 days. Using the Celigo® Cell Imaging Cytometer, percent confluence was tracked daily. On days 5, 6, and 7, MPCs were stained to identify the number of nuclei and the number of dead cells.

Results

PYY protein levels were detectible in MPCs at days 5, 6, and 7 of proliferation. PYY levels were lower on day 7 compared to days 5 (p<0.001) and 6 (p<0.001). Percent confluence area under the curve (days 2–7) was greater in Norm‐PYY compared to both CON (p<0.01) and noFGF (p<0.05) but not High‐PYY. After 7 days of proliferation noFGF cells had fewer nuclei than CON (p<0.05) showing that removal of bFGF reduced proliferative ability of MPCs. In Norm‐PYY, nuclei count was greater (day 7) than noFGF (p<0.001) but not different from CON suggesting that PYY rescued the proliferative ability that was lost when FGF was removed from the media.

Conclusion

MPCs likely synthesize PYY throughout proliferation in a temporal fashion that may be related to the proliferative capacity of the cell. PYY exerts a pro‐proliferative effect on MPCs in culture, possibly, through a mechanism similar to FGF.

Support or Funding Information

Cornell University, Canadian Institute for Health Research Doctoral Foreign Study Award