The Beneficial Effects of Berberine on Vascular Dysfunction in Type 2 Diabetes Are Enhanced by HSP70 Inhibition

Type 2 diabetes (T2D) is a chronic metabolic disorder leading to increased cardiovascular risk and vascular dysfunction. Hyperglycemia, a hallmark of T2D, drives hypercontractility, thereby compromising vascular function. Heat shock protein 70 (HSP70) has emerged as an important player in vascular reactivity under physiological conditions via its interaction with calcium mobilization, and in T2D, blocking this protein prevents hypercontractility. Circulating extracellular HSP70 (eHSP70) has also been proposed as a biomarker in chronic diseases, as it can function as a damage-associated molecular pattern (DAMP) to activate the innate immune system and promote low-grade inflammation. Berberine (BBR), a natural alkaloid with anti-inflammatory properties, has been shown to attenuate vascular contraction by modulating intracellular calcium handling. Yet the link between HSP70 and BBR in modulating vascular contraction in T2D remains unknown. Therefore, we investigated whether acute and/or chronic BBR treatment modulates HSP70 to prevent vascular hypercontractility in the T2D mouse model. For acute ex vivo treatment, db/+ and db/db aortic rings were incubated for 30 min with or without the HSP70 inhibitor VER155008, in the presence or absence of BBR or vehicle. For chronic in vivo treatment, db/+ and db/db mice received intraperitoneal BBR injections (10 mg/kg, 3 times per week) and BBR in their drinking water (0.5 mg/mL) for 28 days. Following chronic (4 weeks, in vivo) or acute ex vivo (30 min) BBR treatment, vascular function was assessed in aortic rings isolated from male T2D (db/db) and age-matched non-diabetic (db/+) mice using wire myography. Rings were incubated with or without the HSP70 inhibitor VER155008, in the presence or absence of BBR or vehicle. Overt hyperglycemia and hypercontractility were observed in diabetic animals compared with non-diabetic controls. While acute BBR treatment attenuated vasoconstriction in both diabetic and nondiabetic groups, the combination of BBR and VER155008 produced a stronger inhibitory effect only in the diabetic group. Chronic BBR treatment prevented aortic hypercontractility in diabetic mice; however, the synergistic effect with VER155008 was no longer observed. Additionally, BBR reduced systemic HSP70 levels. Collectively, these findings indicate that BBR improves vascular smooth muscle cells' function in T2D, at least in part, through HSP70-dependent mechanisms during chronic treatment.