Transglutaminase 2 modulation of NF-κB signaling in astrocytes is independent of its ability to mediate astrocytic viability in ischemic injury

Abstract

Transglutaminase 2 (TG2) is a multifunctional protein that can contribute to cell death and cell survival processes in a variety of disease contexts. Within the brain, TG2 has been shown to promote cell death in ischemic injury when expressed in astrocytes (Colak and Johnson, 2012). However, the specific functions and characteristics of astrocytic TG2 that mediate this effect are largely unknown. Therefore, the goal of this study was to investigate the role of astrocytic TG2 in mediating cellular viability processes in the context of ischemic injury, with a specific focus on its contributions to intracellular signaling cascades. We show that, in response to oxygen/glucose deprivation (OGD), acute lentiviral-mediated knockdown of TG2, as well as inhibition with an irreversible TG2 inhibitor, enhances cell survival. We also show that TG2 depletion increases nuclear factor-κB (NF-κB) signaling, whereas inhibition reduces NF-κB activity. Despite its clear contribution to NF-κB signaling, however, TG2 modulation of NF-κB signaling is not likely to be a major contributor to its ability to mediate astrocytic viability in this context. Overall, the results of this study provide insight into the role of TG2 in astrocytes and suggest possible avenues for future study of the relationship between astrocytic TG2 and ischemic injury.

Subcellular localization patterns of transglutaminase 2 in astrocytes and neurons are differentially altered by hypoxia

“…Primary cortical astrocytes were harvested at P0 from mice as previously described [2,10]. Astrocytes were maintained in MEM media supplemented with 10% FBS, 6 g/L glucose, 1 mM sodium pyruvate, and 25 μg/mL Gentamicin (Glia MEM) prior to use in experiments.…”

“…The astrocyte cultures are maintained in serum and passaged once before being used. This results in cultures that contain >95% astrocytes [2,10]. …”

“…TG2 was first identified as a Ca 2+ -dependent transamidating enzyme, but subsequent studies have demonstrated that it also can function as a GTPase, a protein disulfide isomerase and a scaffold or linker protein [4–6]. Intriguingly the ability of TG2 to protect neurons against ischemic stress is not dependent on transamidating activity [7,8], while the ability of TG2 to facilitate astrocyte migration [9] or potentiate ischemic-induced cell death [10] requires TG2’s transamidating activity. Further, its ability to mediate cell death and survival processes has been suggested to be dependent, in part, on its subcellular localization [11–15].…”

Transglutaminase 2: Friend or foe? The discordant role in neurons and astrocytes

“…When astrocytes were cocultured with neurons it was found that TG2–/– astrocytes were able to protect wild‐type or TG2–/– neurons from OGD‐induced cell death to a significantly greater extent than wild‐type astrocytes (Colak & Johnson, ). In further studies, it was also found that knocking down TG2 in astrocytes with TG2 shRNA also significantly increased their viability following OGD (Feola et al, ) and their ability to protect neurons. While further investigation is needed, one possible explanation for this phenomenon could be that TG2 knockout in astrocytes could result in changes in the metabolic pathways that produce products that are released to protect neurons.…”

Nuclear transglutaminase 2 directly regulates expression of cathepsin S in rat cortical neurons

“…Whether TG2 is beneficial or detrimental to cell survival is dependent on the cell type and stressors. In astrocytes, TG2 facilitates ischemic cell death as TG2 deletion or knockdown supports survival in an oxygen and glucose deprivation (OGD) paradigm (Colak & Johnson, ; Feola, Barton, Akbar, Keillor, & Johnson, ). In contrast to its detrimental role in astrocytes, TG2 supports neuron survival.…”