Association between IGF-1 and IGFBPs in Blood and Follicular Fluid in Dairy Cows Under Field Conditions

Abstract

Insulin-like growth factor 1 (IGF-1) regulates dairy cow reproduction, while the paracrine IGF system locally influences fertility. In both systems, IGF-1 bioactivity is regulated through binding proteins (IGFBPs) inhibiting IGF-1 binding to its receptor (IGF1R). This study aimed to investigate a possible transfer between this endocrine and paracrine system. Therefore, blood and follicular fluid (FF) from postpartum dairy cows were analysed for ß-hydroxybutyrate (BHB), IGF-1, IGFBP-2, -3, -4, -5, and an IGFBP fragment in two study parts. The mRNA expression of IGFBP-2, IGFBP-4, IGF1R, and the pregnancy-associated plasma protein A (PAPP-A) in granulosa cells was measured. The results showed correlations between plasma and FF for IGF-1 (r = 0.57, p < 0.001) and IGFBP-2 (r = -0.57, p < 0.05). Blood BHB negatively correlated with IGF-1 in blood and FF and IGFBP-3, -5 and total IGFBP in blood (IGF-1 plasma: r = -0.26, p < 0.05; FF: r = -0.35, p < 0.05; IGFBP-3: r = -0.64, p = 0.006; IGFBP-5: r = -0.49, p < 0.05; total IGFBP: r = -0.52, p < 0.05). A negative correlation was found between IGFBP-2 expression and IGF-1 concentration in FF (r = -0.97, p = 0.001), while an IGFBP fragment positively correlated with IGF1R-mRNA in FF (r = 0.82, p = 0.042). These findings suggest a transfer and local regulation between the somatotropic axis and the follicular IGF system, linking the metabolic status with local effects on dairy cow fertility.

Keywords: IGF-1; IGFBP; cattle; dairy cow; fertility; metabolic status; somatotropic axis.

Figure 1

Example of a Western ligand blot with standards and samples; IGFBP = insulin-like growth factor binding protein, Gel no. 4_a: representation of IGFBP-3 in the standard and the IGFBPs in the samples separated according to their molecular size; IGFBP in plasma and follicular fluid (IGFBP-2,-3,-4, and -5 and an IGFBP fragment that has bound biotinylated IGF-2), _a: A21 results of the IGFBP analysis, Gel 141, 01.06.2022, Ligandis UG (Gülzow-Prüzen, Germany).

Figure 2

(A) IGF-1 in follicular fluid plotted against IGF-1 in plasma, IGF-1 = insulin-like growth factor 1, FF = follicular fluid, FF from study part I, ○, mean IGF-1 if more than one follicle/animal, n = 16, 109.64 ± 32.58 ng/mL, day 65 ± 16 p.p., FF from study part II, ●, n = 24, 68.79 ± 31.46 ng/mL, day 32 ± 3 p.p., Plasma from study part I, ○, n = 16, 158.90 ± 36.99 ng/mL, day 65 ± 16 p.p., plasma from study part 2 ●, n = 25, 133.27 ± 48.85 ng/mL, day 32 ± 3 p.p., with regression line; (B) IGFBP-2 in follicular fluid plotted against IGFBP-2 in plasma; IGFBP-2 = insulin-like growth factor binding protein 2; FF = follicular fluid, FF from study part I, mean IGFBP-2 if more than one follicle/animal, ○, n = 17, 578.4/1701/15.69 ng/mL, day 65 ± 16 p.p.; plasma from study part I, ○, n = 17, 1707 ± 904.7 ng/mL, day 65 ± 16 p.p.

Figure 3

(A) IGFBP-3 and BHB in blood, study part I, IGFBP = insulin-like growth factor binding protein, BHB = β-hydroxybutyric acid, FF = follicular fluid, study part I, n = 17; with regression line, day 65 ± 16 postpartum (p.p.); (B) IGFBP-5 and BHB in blood; study part I, n = 17, day 65 ± 16 p.p.; (C) IGFBP-total and BHB in blood; study part I, n = 17; with regression line; day 65 ± 16 p.p; (D) BHB and IGF-1 in blood, study part I ○, n = 72, day 30 ± 2 p.p., study part II ●, n = 22, day 32 ± 3 p.p.; with regression line, nine outliers eliminated (BHB ≥ 2.2 mmol/L); (E) IGF-1 in FF and BHB in blood, study part I: ○, in FF mean IGF-1 if more than one follicle/animal, n = 17; study part II: ●, n = 20); with regression line, four outliers eliminated (BHB ≥ 1.8 mmol/L).

Figure 4

Shares of IGFBP in plasma and follicular fluid, study part I; IGFBP = insulin-like growth factor binding protein, FF = follicular fluid, study part I, in plasma (n = 17, IGFBP-2: 30.9/53/21%; IGFBP-3: 44.7 ± 8.2%; IGFBP-4: 5.4 ± 3%; IGFBP-5: 13.8 ± 3.1%; IGFBP-F: 5.2 ± 2.4%) and FF (n = 27, IGFBP-2: 13.8/36.3/0.5%; IGFBP-3: 47.6 ± 9.4%; IGFBP-4: 6.4/25.79/0.9%; IGFBP-5: 21.8 ± 8.6%; IGFBP-F: 10.27 ± 3.2%), percentage shares without a common letter (a, b) differ significantly between plasma and FF: IGFBP-5 (p = 0.001), IGFBP-2 (p < 0.001) and IGFBP-F (p < 0.001).

Figure 5

(A) Relative IGFBP-2 gene expression in granulosa cells (GC) plotted against IGF-1 in follicular fluid, FF, and granulosa cells from study part I; n = 6; with regression line IGFBP = insulin-like growth factor binding protein; FF = follicular fluid. (B) Relative IGF-1 receptor gene expression in granulosa cells plotted against IGFBP-F in follicular fluid, FF, and granulosa cells from study part I; n = 6, with regression line; IGFBP = insulin-like growth factor binding protein; FF = follicular fluid.