Mesangial cells are specialized cells found within the kidney’s filtering units, known as glomeruli, specifically in the mesangium. They contribute to the kidney’s overall integrity and function by supporting the delicate filtering structures. Without properly functioning mesangial cells, the kidney’s ability to purify blood and maintain fluid balance would be compromised.
Understanding Mesangial Cell Structure
Mesangial cells have an irregular, often star-shaped appearance with processes extending from their bodies. These processes contain contractile proteins such as actin, myosin, and actinin, giving the cells smooth muscle-like properties. Located in the mesangium between the glomerular capillaries, they interact closely with the capillary loops and the glomerular basement membrane, forming a scaffolding that holds the delicate capillary network together.
The mesangium consists of mesangial cells embedded in an extracellular matrix they produce. This matrix contains various proteins, including type IV collagen, fibronectin, laminin, and proteoglycans, providing further structural support. There are two main categories of mesangial cells: intraglomerular mesangial cells (inside the glomerulus among the capillaries) and extraglomerular mesangial cells (found between the afferent and efferent arterioles at the vascular pole). These cells are in close communication with other glomerular cells, such as endothelial cells and podocytes, forming a functional unit that coordinates filtration.
How Mesangial Cells Maintain Kidney Health
Mesangial cells provide structural support to the glomerular capillaries, preventing their collapse under blood flow pressure. This ensures the stable architecture necessary for efficient filtration. This structural integrity is maintained partly by anchoring filaments that connect mesangial cells to the glomerular basement membrane.
Beyond their supportive role, mesangial cells possess contractile properties, allowing them to regulate blood flow and the filtration surface area within the glomerulus. They can contract or relax in response to various vasoactive substances, influencing the rate at which blood is filtered. This dynamic regulation of filtration surface area by mesangial cell contraction helps to modify the glomerular filtration rate (GFR).
Mesangial cells also perform a phagocytic function, engulfing and removing trapped macromolecules, immune complexes, and debris from the glomerular filtration barrier. This “cleaning” activity helps to keep the filter free of obstructions, maintaining its efficiency. They can internalize these substances through various uptake processes. This clearance mechanism is important for preventing the accumulation of waste products and immune deposits that could otherwise impair kidney function.
Mesangial Cells and Kidney Disease
When mesangial cells malfunction, it can contribute to various kidney diseases, leading to impaired kidney function. One significant condition is diabetic nephropathy, a common complication of diabetes. In this disease, mesangial cells proliferate and produce an excessive amount of extracellular matrix, leading to mesangial matrix expansion. This expansion, characterized by increased deposition of extracellular matrix proteins, can cause glomerulosclerosis, or scarring of the glomerulus. The accumulation of this matrix and the proliferation of mesangial cells can reduce the glomerular filtration rate, ultimately leading to kidney failure.
Mesangial cells are also involved in various forms of glomerulonephritis, which are inflammatory kidney diseases. In conditions like IgA nephropathy, immune complexes deposit in the mesangium, activating mesangial cells. This activation can lead to mesangial cell proliferation, further extracellular matrix expansion, and the release of inflammatory mediators. Similar processes occur in lupus nephritis, where immune complex deposition in the mesangium causes mesangial cell damage, leading to excessive proliferation and increased extracellular matrix production. The inflammation and cellular changes in glomerulonephritis can impair the kidney’s ability to filter blood effectively, often resulting in symptoms like reduced filtration and proteinuria.