Calpain inhibition restores autophagy and protects blood vessels in diabetes

New research highlights how calpains, calcium-activated enzymes, impair cellular waste disposal in blood vessel cells under diabetic conditions, offering a promising target for preventing vascular damage.

A new study in Cellular and Molecular Life Sciences suggests that calpains, a family of calcium-activated enzymes, help drive the vascular damage linked to diabetes by disrupting the cell’s waste-clearing machinery. The research, led by Yann Salemkour and Olivia Lenoir, points to a failure of autophagy, the process that disposes of damaged proteins and organelles, as a key step in the deterioration of the endothelium, the thin layer of cells that lines blood vessels and helps regulate circulation.

The findings build on earlier work showing that calpain activity rises in diabetic endothelial cells and that blocking it can limit oxidative stress and improve vessel function. In this study, the researchers examined human umbilical vein endothelial cells and primary lung endothelial cells exposed to high glucose, a laboratory model of diabetic conditions. They found that calpains became overactive and that autophagic flux stalled, meaning the cell’s recycling system could no longer clear cellular debris efficiently. As a result, the cargo receptor SQSTM1, also known as p62, accumulated, LC3B levels fell and mitochondria became fragmented rather than remaining in a healthy network.

To test whether calpains were causing the damage, the team used both drugs that inhibit the enzymes and calpastatin, the body’s own calpain blocker. Both approaches restored autophagy and preserved mitochondrial structure, making the evidence for a causal role stronger than if the researchers had relied on a single method. The study also found that calpain inhibition countered several hyperglycaemia-driven stress programmes, including oxidative phosphorylation, reactive oxygen species signalling and the unfolded protein response, which is triggered when the endoplasmic reticulum is under strain.

The work adds a new layer to a problem long associated with diabetes. Endothelial dysfunction is a central mechanism behind heart attacks, strokes, kidney disease and other complications, and previous studies have already linked calpain activation to excess reactive oxygen species, reduced nitric oxide availability and impaired endothelium-dependent relaxation. One earlier report in the journal Diabetes found that suppressing calpain through calpastatin improved vascular relaxation in diabetic mice, while another study in Cardiovascular Diabetology showed that calpain inhibition reduced mitochondrial superoxide production and apoptosis in endothelial cells exposed to high glucose.

The new paper goes further by tying calpain activity specifically to autophagy and mitophagy, the selective removal of damaged mitochondria. In animal experiments, the researchers reported that restraining calpain preserved vascular reactivity in diabetic mice, suggesting that the cellular rescue seen in the laboratory translated into measurable protection in living tissue. The study also used mitoQC reporter mice, developed in Ian Ganley’s laboratory at the University of Dundee, to visualise mitophagy directly in vivo and confirm the cellular results.

The implications are promising but still preclinical. Calpains are involved in several normal biological processes, including platelet activation, muscle remodelling and neuronal function, so any treatment aimed at blocking them would need to balance benefit against the risk of wider effects. Even so, the combination of cell-based experiments, gene-expression analysis and animal data strengthens the case that calpains sit at an important control point in diabetic vascular disease. For researchers trying to understand how high blood sugar damages blood vessels, the study offers a clear target and a plausible route towards therapies that might protect the endothelium before irreversible harm sets in.