Regulation of intestinal permeability: The role of proteases

Table 1 Overview of proteases affecting intestinal permeability

Protease	Effect	Model	Mechanism of action	Ref.
Serine proteases
Matriptase	Protective	ST14 hypomorphic mice	Genetic depletion of matriptase induces an increase in intestinal permeability (decreased TER and increased FITC-dextran flux)	[65, 66]
		Epithelial cell monolayer	Inhibition of matriptase with silencing RNA and the synthetic inhibitor MI-432 increased the intestinal permeability (decreased TER and increased FITC-dextran flux)	[65, 68]
Granzyme M	Protective	GrzM-/- mice	GrzM-/- mice display a permeability increase (FITC-dexran method)	[73]
Zonulin, Zonula occludens toxin (Zot)	Harmful	Human epithelial cell monolayer	↑ Permeability after exposure to gliadin (triggers zonulin release; disruption of occludin and ZO-1)	[76]
		Ileal tissue of diabetes prone rats	Zonulin-dependent permeability increase in diabetic rats was abolished after oral treatment with zonulin inhibitor FZI/0 (AT1001/Larazotide)	[82]
PAR2 activation
Trypsin, tryptase, chymase, synthetic SLIGRL	Harmful	WT mice, WT rats	↑ Permeability due to PAR2 activation (confirmed by selective PAR2 agonist SLIGRL; increased 51Cr-EDTA flux)	[47, 48, 51]
PAR4 activation
Cathepsin G	Harmful	Colonic biopsies from UC and healthy patients	↑ Permeability in response to UC fecal supernatant was abolished by cathepsin G inhibition	[58]
PAR1 activation
Thrombin, synthetic TFLLR-NH2	Harmful	WT mice, epithelial cell monolayer	↑ Permeability after PAR1 activation (caspase-3 mediated; disruption of ZO-1)	[62]
Endogenous inhibitors
Elafin	Protective	Gluten sensitive mice	↓ Permeability after elafin delivery by recombinant Lactococcus lactis (51Cr-EDTA flux)	[87]
		Human epithelial cell monolayer	Treatment with elafin normalized the TNF-α-induced increase in paracellular permeability (FITC-dextran method)	[88]
Synthetic inhibitors
Camostat mesilate	Protective	Rat IBS model	Treatment with camostat mesilate normalized the elevated permeability in the rats (51Cr-EDTA flux and ZO-1 expression)	[89]
Nafamostat mesilate	Protective	Rectal biopsies from IBS and healthy patients	Nafamostat abolished the trypsin-induced hyperpermeability (macromolecular flux in Ussing chambers)	[94]
		Human epithelial cell monolayer	Treatment with nafamostat normalized the tryptase-induced permeability increase (TER and FITC-dextran method)	[95]
SPI	Protective	IBD mouse model	Treatment with SPI normalized the increased permeability in the T-cell transfer colitis model (FITC-dextran method)	[96]
Metalloproteases
Meprin β	Protective	Mep1b-/- mice	Meprin β cleaves MUC2 and alters mucus composition	[128, 129]
Matrix metalloproteinases
MMP-2	Protective	MMP-2-/- mice	↑ permeability in MMP-2-/- mice (FITC-dextran method)	[111]
MMP-9	Harmful	MMP-9-/- mice	= Permeability in MMP-9-/- mice after DSS (FITC-dextran method; no increase in MLCK expression)	[114]
		MMP-9-/- mice	↑ Goblet cells and MUC2 expression in MMP-9-/- mice	[113]
		MMP-9 transgenic mice	↑ Permeability in mice overexpressing MMP-9 (FITC-dextran method)	[112]
MMP-3, MMP-7	Harmful	Epithelial cell culture	MMP-7 cleaves E-cadherin	[121]
ADAM
TACE/ADAM17	Harmful	Human and mouse colon samples	↑ TACE activity in IBD; ↑ TNF-α release; ↑ TNF-α-induced permeability increase	[131, 134, 135]
		Caco-2	↓ Permeability after TACE inhibition (by TAPI-2 and GM6001)	[136]
Cysteine proteases
Caspase-3, caspase-8	Harmful	Human epithelial cell monolayer	↓ Cell-cell adhesion (epithelial cell apoptosis; disruption of TJ proteins occludin and claudin-4)	[144]
Endogenous inhibitor
Cystatin	No effect	WT mice	No effect on colonic paracellular permeability (51Cr-EDTA flux)	[51]
Luminal proteases
Bacteroides fragilis
Fragilysin	Harmful	Human epithelial cell monolayer	↑ Permeability (decreased TER and increase in mannitol flux)	[149, 150]
Entamoeba histolytica
Cysteine protease	Harmful	Mice transfected with E. histolytica trophozoites	↑ Permeability (FITC-dextran method)	[151]
Enterococcus faecalis
Gelatinases	Harmful	IL10-/- mice	↑ Permeability (E-cadherin splicing)	[156]
		Epithelial cell monolayers	↑ Permeability (PAR2 signaling)	[155]
Dermatophagoides pteronyssinus
Der p 1	Harmful	Human colonic biopsies	↑ Permeability (decreased TER in Ussing chambers; disruption of TJ proteins occludin and ZO-1	[158]
Kiwifruit cysteine protease
Act d1	Harmful	Epithelial cell monolayer	↑ Permeability (disruption of TJ proteins occludin and ZO-1)	[162]
		WT mice	↑ Permeability (FITC-dextran method)	[161]
Aspergillus
Amano SD	Protective	WT rat	Improved mucosal homeostasis through alteration of the microbiome composition and SCFA induction	[163]

TJ: Tight junction; PARs: Proteinase-activated receptors; MLC: Myosin light chain; MLCK: Myosin light chain kinase; PKC: Protein kinase C; ROCK: Rho-associated protein kinase; ZO-1: Zonula occludens 1.