Paracellular barriers: Advances in assessing their contribution to renal epithelial function

Area of Science:

• Physiology
• Molecular Biology
• Comparative Anatomy

Background:

• Salt and water balance is crucial for animal physiology, relying heavily on renal system function.
• Mammalian kidneys utilize intercellular tight junctions (TJs) to regulate epithelial ion and water transport via transcellular and paracellular pathways.
• Insect Malpighian tubules, unlike mammalian nephrons, employ smooth septate junctions (sSJs) as their primary paracellular barrier.

Purpose of the Study:

• To highlight key concepts in paracellular barrier function.
• To present recent findings on the molecular and functional dissection of renal paracellular barriers.
• To compare TJ function in mammals with sSJ function in insects.

Main Methods:

• Review of current literature on TJ and sSJ structure and function.
• Comparative analysis of paracellular transport mechanisms in mammalian and insect renal epithelia.
• Focus on claudin proteins in mammalian TJ plasticity.

Main Results:

• Tight junctions (TJs) in mammals, modulated by claudin proteins, exhibit functional plasticity in regulating solute and water passage.
• Smooth septate junctions (sSJs) in insects serve as the paracellular barrier in Malpighian tubules, with their properties still under investigation.
• Research in model species is beginning to elucidate the molecular and functional characteristics of sSJs.

Conclusions:

• Understanding paracellular barriers is essential for comprehending renal physiology across different species.
• Comparative studies of TJs and sSJs offer insights into the evolution and diversity of epithelial transport.
• Further research into sSJ molecular components is needed to fully understand insect renal function.