Double Knockdown of the Androgen Receptor Target Genes DKK1 and SFRP1 Does Not Potentiate the Hair Growth-Promoting Effect of SFRP1 Silencing in Healthy Human Hair Follicles Ex Vivo

Androgen receptor (AR) signaling plays a key role in male pattern baldness. We investigated whether targeting <i>Dickkopf 1</i> (<i>DKK1</i>) and <i>Secreted frizzled-related protein 1</i> (<i>SFRP1</i>), two AR-regulated genes, offers a novel therapeutic strategy for hair loss. AR expression was validated in freshly frozen human scalp hair follicles (HFs). <i>AR</i> knockdown was induced in human HFs using AR spherical nucleic acid (SNA). <i>DKK1</i> and <i>SFRP1</i> siRNA treatment were performed in HEK293 cells, human dermal papilla cells (hDPC), and human HFs ex vivo. Functional effects of single and combined <i>DKK1</i> and <i>SFRP1</i> knockdown were analyzed in human HFs ex vivo by quantitative (immuno)histomorphology. <i>AR</i> knockdown decreased <i>SFRP1</i> and <i>DKK1</i> expression. We found reciprocal mRNA upregulation between <i>DKK1</i> and <i>SFRP1</i> following their siRNA knockdown in HEK293 and hDPC. We therefore applied a single and combined treatment of <i>DKK1</i> and <i>SFRP1</i> siRNA in HFs ex vivo. <i>SFRP1</i> knockdown prolonged anagen, increased hair matrix keratinocyte proliferation, reduced apoptosis, and increased DKK1 levels in HFs ex vivo, whereas <i>DKK1</i> knockdown had no effect, and combined knockdown did not enhance SFRP1's benefits. The culture-dependent compensatory regulation of <i>SFRP1</i> and <i>DKK1</i> underscores Wnt-signaling complexity in hair growth and strengthens the rationale for SFRP1 based therapies in anagen maintenance and hair loss.