The Effect of Vitamin D3 Injection Combined With High‐Intensity Interval Training on Excessive Autophagy in the Heart Tissue of Type 2 Diabetes–Induced Rats: An Analysis of the mTOR–Beclin‐1–Fyco‐1–Cathepsin D Pathway

<b>Introduction:</b> This study investigated the effect of vitamin D3 injection combined with high-intensity interval training on cell signaling pathways involved in excessive autophagy, specifically the mTOR (mechanistic target of rapamycin)-Beclin-1-Fyco-1 (FYVE and coiled-coil domain-containing protein 1)-cathepsin D pathway, in the heart tissue of Type 2 diabetes-induced rats. <b>Method:</b> In this experimental study, 32 male Wistar rats were fed a high-fat diet for 6 weeks to induce Type 2 diabetes, followed by a single subcutaneous injection of 35 mg/kg streptozotocin (STZ). The rats were then randomly assigned to one of four groups: (1) diabetes control (DC), (2) diabetes + HIIT (DT), (3) diabetes + vitamin D3 (DV), and (4) diabetes + HIIT + vitamin D3 (DTV). HIIT sessions were conducted for 8 weeks, five times per week, at an intensity of 85%-95% of maximum running speed (<i>V</i> _max), while vitamin D3 was administered weekly via subcutaneous injection at a dose of 10,000 IU/kg. Twenty-four hours after the intervention period, heart and left ventricular tissues were collected for analysis of the levels of autophagy signaling proteins mTOR, phosphorylated mechanistic target of rapamycin (pmTOR), Beclin-1, Fyco-1, and cathepsin D. <b>Results:</b> Two-way ANOVA revealed that Type 2 diabetes significantly increased the levels of Beclin-1, Fyco-1, and cathepsin D (<i>p</i> < 0.001) while significantly reducing the levels of mTOR and pmTOR (<i>p</i> < 0.001). HIIT, vitamin D3 injection, and their combined treatment significantly decreased the levels of Beclin-1, Fyco-1, and cathepsin D and increased the levels of mTOR and pmTOR compared to the diabetes control group (<i>p</i> < 0.001). <b>Conclusion:</b> Type 2 diabetes increases autophagy in the left ventricle, marked by altered levels of key autophagy proteins. HIIT and vitamin D3 injections mitigate these effects by enhancing mTOR signaling and reducing excessive autophagy. These interventions show promise as nonpharmacological strategies to improve cardiac health in Type 2 diabetes and could be incorporated into clinical and rehabilitation programs.