Increased Retinoic Acid Catabolism in Olfactory Sensory Neurons Activates Dormant Tissue-Specific Stem Cells and Accelerates Age-Related Metaplasia

The cellular and molecular basis of metaplasia and declining neurogenesis in the aging olfactory epithelium (OE) remains unknown. The horizontal basal cell (HBC) is a dormant tissue-specific stem cell presumed to only be forced into self-renewal and differentiation by injury. Here we analyze male and female mice and show that HBCs also are activated with increasing age as well as non-cell-autonomously by increased expression of the retinoic acid-degrading enzyme CYP26B1. Activating stimuli induce HBCs throughout OE to acquire a rounded morphology and express IP3R3, which is an inositol-1,4,5-trisphosphate receptor constitutively expressed in stem cells of the adjacent respiratory epithelium. Odor/air stimulates CYP26B1 expression in olfactory sensory neurons mainly located in the dorsomedial OE, which is spatially inverse to ventrolateral constitutive expression of the retinoic acid-synthesizing enzyme (RALDH1) in supporting cells. In ventrolateral OE, HBCs express low p63 levels and preferentially differentiate instead of self-renewing when activated. When activated by chronic CYP26B1 expression, repeated injury, or old age, ventrolateral HBCs diminish in number and generate a novel type of metaplastic respiratory cell that is RALDH^- and secretes a mucin-like mucus barrier protein (FcγBP). Conversely, in the dorsomedial OE, CYP26B1 inhibits injury-induced and age-related replacement of RALDH^- supporting cells with RALDH1⁺ ciliated respiratory cells. Collectively, these results support the concept that inositol-1,4,5-trisphosphate type 3 receptor signaling in HBCs, together with altered retinoic acid metabolism within the niche, promote HBC lineage commitment toward two types of respiratory cells that will maintain epithelial barrier function once the capacity to regenerate OE cells ceases.SIGNIFICANCE STATEMENT Little is known about signals that activate dormant stem cells to self-renew and regenerate odor-detecting neurons and other olfactory cell types after loss due to injury, infection, or toxin exposure in the nose. It is also unknown why the stem cells do not prevent age-dependent decline of odor-detecting neurons. We show that (1) stem cells are kept inactive by the vitamin A derivative retinoic acid, which is synthesized and degraded locally by olfactory cells; (2) old age as well as repeated injuries activate the stem cells and exhaust their potential to produce olfactory cells; and (3) exhausted stem cells alter the local retinoic acid metabolism and maintain the epithelial tissue barrier by generating airway cells instead of olfactory cells.

Activation of calcium signaling in human gingival fibroblasts by recombinant Porphyromonas gingivalis RgpB protein

Arginine-specific cysteine proteinases, such as Arg-gingipain B (RgpB), mediate inflammation by activating protease-activated receptors (PARs). Arg-gingipain B is produced by Porphyromonas gingivalis, and is implicated in the causation of periodontal disease. The purpose of the present study was to observe the influence of recombinant RgpB protein (rRgpB) on PAR activation by monitoring intracellular Ca2+ ion concentration ([Ca2+]i) and inositol-1,4,5-triphosphate (IP3) levels in human gingival fibroblasts (HGFs). Our findings showed that rRgpB could cause a transient increase in [Ca2+]i. This increase in [Ca2+]i was completely suppressed by vorapaxar, a PAR-1 antagonist. Recombinant Arg-gingipain B increased the concentration of IP3, reaching a maximum at 60 s after treatment; this was completely inhibited by vorapaxar. We therefore conclude that rRgpB-induced calcium signaling in HGFs is mainly caused by PAR-1 activation. This suggests that PAR-1 activation plays a significant role in chronic inflammatory periodontal disease induced by P. gingivalis RgpB.

Carbamazepine suppresses calpain-mediated autophagy impairment after ischemia/reperfusion in mouse livers. Toxicol Appl Pharmacol. 2013;273:600-610. [PMID: 24126417 DOI: 10.1016/j.taap.2013.10.006]

Onset of the mitochondrial permeability transition (MPT) plays a causative role in ischemia/reperfusion (I/R) injury. Current therapeutic strategies for reducing reperfusion injury remain disappointing. Autophagy is a lysosome-mediated, catabolic process that timely eliminates abnormal or damaged cellular constituents and organelles such as dysfunctional mitochondria. I/R induces calcium overloading and calpain activation, leading to degradation of key autophagy-related proteins (Atg). Carbamazepine (CBZ), an FDA-approved anticonvulsant drug, has recently been reported to increase autophagy. We investigated the effects of CBZ on hepatic I/R injury. Hepatocytes and livers from male C57BL/6 mice were subjected to simulated in vitro, as well as in vivo I/R, respectively. Cell death, intracellular calcium, calpain activity, changes in autophagy-related proteins (Atg), autophagic flux, MPT and mitochondrial membrane potential after I/R were analyzed in the presence and absence of 20 μM CBZ. CBZ significantly increased hepatocyte viability after reperfusion. Confocal microscopy revealed that CBZ prevented calcium overloading, the onset of the MPT and mitochondrial depolarization. Immunoblotting and fluorometric analysis showed that CBZ blocked calpain activation, depletion of Atg7 and Beclin-1 and loss of autophagic flux after reperfusion. Intravital multiphoton imaging of anesthetized mice demonstrated that CBZ substantially reversed autophagic defects and mitochondrial dysfunction after I/R in vivo. In conclusion, CBZ prevents calcium overloading and calpain activation, which, in turn, suppresses Atg7 and Beclin-1 depletion, defective autophagy, onset of the MPT and cell death after I/R.