Fig. 1: Secretory leukocyte protease inhibitor (SLPI) controls the parathyroid hormone (PTH)-induced increase in bone mass.

a RNA-sequencing (RNA-Seq) scatter plot of differential expression between vehicle-treated osteoblasts and intermittent parathyroid hormone (PTH)-treated osteoblasts (log₁₀-transformed fragments per kilobase of transcript per million mapped reads [FPKM]). b mRNA levels of Slpi in 7AAD⁻ Lin⁻ CD45⁻ ECFP⁺ osteoblasts as determined by quantitative polymerase chain reaction (qPCR) analysis (n = 4 biologically independent samples per group). c mRNA levels of Slpi as determined by qPCR analysis (n = 5 mice per group for the analysis of MSC, and n = 3 mice per group for the analysis of total BM, Mono/Mφ, and granulocytes). MSC, mesenchymal stem cells (Lin⁻ CD45⁻ CD31⁻ Sca1⁺ CD51⁺ population); BM, total bone marrow cells; Mono/Mφ, monocyte/macrophage (CD45⁺ Ly6G⁺ population); granulocytes (CD45⁺ Ly6G⁻ F4/80⁺ population). d–g Representative micro-computed tomography images of the femurs. Scale bar, 1000 µm. h Ratio of bone volume to total bone volume (BV/TV), and trabecular thickness (Tb.Th) values (n = 7 mice per group). i Serum type I procollagen N-terminal propeptide (P1NP) levels, as measured by enzyme-linked immunosorbent assay (ELISA) (WT PBS: n = 4 mice, WT PTH: n = 4 mice, Slpi-KO PBS: n = 5 mice, Slpi-KO PTH: n = 4 mice). j Serum type I procollagen C-terminal telopeptide (CTX) levels, as measured by ELISA (WT PBS: n = 8 mice, WT PTH: n = 5 mice, Slpi-KO PBS: n = 7 mice, Slpi-KO PTH: n = 7 mice). k Histological analysis of the proximal tibias. Images are toluidine blue-stained sections (Representative image, n = 3 biologically independent experiments). Scale bars, 500 µm. l Merged image of the calcein band and bright field of the proximal tibias (Representative image, n = 3 biologically independent experiments). Scale bar, 50 µm. m Bone formation rate (BFR/BS) values (WT PBS: n = 6 mice, WT PTH: n = 5 mice, Slpi-KO PBS: n = 6 mice, Slpi-KO PTH: n = 5 mice). For details and statistical analysis, see Table S2. Data are means ± SEM. NS, not significant. Statistical significance was determined by ANOVA with Dunnett’s test (b), Tukey’s test (h, i, j), Šidák’s test (m), and two-tailed Student’s t-test (c). h P₁ exact value = 2.8E⁻⁷, P₂ exact value = 8.5E⁻¹², P₃ exact value = 2.8E⁻⁹, P₄ exact value = 5.1E⁻⁶, P₅ exact value = 2.0E⁻¹⁰, P₆ exact value = 9.5E⁻⁸.