OR27-01 Upregulated Prdm16 Impairs Adipogenesis And Promotes Myogenesis Via PAX7 And Osteogenesis In Testosterone-treated Hypogonadal Men

Disclosure: S. Bathina: None. M. Prado: None. L. Aguirre: None. G. Colleluori: None. E. Ballato: None. F. Deepika: None. V. Fuenmayor Lopez: None. D.T. Villareal: None. R.A. Villareal: None. Background: Testosterone (T) therapy increases lean mass; reduces total body and truncal fat mass and increases bone density in hypogonadal men. However, the underlying mechanisms for these changes remain unclear. In this study, we investigated the mechanisms involved for these effects of T on body composition and bone. Objective: Our aims are to evaluate the changes in 1) the gene and protein machinery involved the adipo-myogenic switch, and 2) the cellular osteogenic markers, in-vivo, in response to T therapy. Methods and Study design: Secondary analysis of specimens obtained from a single-arm, open-label clinical trial (NCT01378299) on pharmacogenetics of response to T therapy conducted between 2011-2016 N=105 men (40-74 years old), with average morning T <300 ng/dL who were given intramuscular T cypionate 200 mg every 2 weeks for 18 months As earlier results from our lab, effect of T therapy is maximal after 6 months, we chose to study the specimens at baseline (BL) and 6 months (6M). We measured the adipogenic transcription factors (PPARγ, CEBPa), enzymes (LPL, Adipsin) from subcutaneous fat, and myogenic lineage (Myf5, MyoD), Prdm16 and Pax7 from buffy coat by real-time quantitative PCR at BL and 6M. Serum Follistatin, PRDM16, PAX7 Myostatin, Adipsin were measured by ELISA. Changes in circulating osteogenic precursors (COP) and osteoclast precursors (OCPs) by Flow cytometry, and gene expression of osteoblastic transcription factor, Runx2, by PCR of buffy coat. OCPs in response to testosterone therapy were evaluated from samples of men participating in an ongoing clinical trial (NCT03887936). Results: T therapy decreased PPARg (BL: 2.59±2.2 vs 6M: 1.23±1.0, p=0.03); CEBPa (BL: 3.0±2.57 vs 6M: 1.7±1.2, p=0.10) LPL (BL: 2.81±2.7 vs 6M: 1.74±2.2, p=0.27) in sub-cutaneous fat tissue and increased the expression of MyoD (BL:1.34±1.6 vs 6M: 8.2±12.7, p=0.02) and Myf5 (BL: 6.1±9.7 vs 6M: 12.9±27.7, p=0.26) along with the adipo-myogenic switch, Prdm16 (BL: 1.8±1.9 vs 6M: 4.5±4.1, p< 0.01); Pax7 (BL:1.3±0.8 vs 6M: 1.9±2.0, p=0.2) in buffy coat. T therapy also increased serum Follistatin (BL:2031±1483 vs 6M: 3396 ± 1662pg/ml, p=0.009), the myogenic regulator, PAX7 (BL:21.5±1.9 vs 6M: 34±2.2ng/ml, p=0.002); and PRDM16 (BL:0.20±0.10 vs 6M: 0.49±0.26ng/ml, p=0.29) and decreased serum Myostatin (BL: 3218±738 vs 6M: 2714±62.2pg/ml, p=0.42) Adipsin (BL:15929±10209 vs 6M:12101±4865ng/ml p=0.04). COPs increased in T-treated (T) compared to Placebo (P); (P (6M): -4.3±57 vs T(6M): -20.2±44, p=0.20 & P(12M): -15.7±44.5 vs T(12M): 47.4±74.8, p=0.02)) and Runx2 expression increased (BL: 1.26±0.86 vs 6M: 2.17±1.6, p=0.03). Conclusions: Our results suggested that reciprocal effect of T-therapy on fat mass and lean mass is not only due to shift from adipogenesis to myogenesis but also due to enhanced osteogenesis. Thus, this study can provide unifying mechanism for observed effect of T in hypogonadal men. Presentation Date: Saturday, June 17, 2023