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Article

HspB4/αA-Crystallin Modulates Neuroinflammation in the Retina via the Stress-Specific Inflammatory Pathways

1
Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA
2
Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48105, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Rafael Simó
J. Clin. Med. 2021, 10(11), 2384; https://doi.org/10.3390/jcm10112384
Received: 9 April 2021 / Revised: 14 May 2021 / Accepted: 24 May 2021 / Published: 28 May 2021
(This article belongs to the Special Issue State-of-the-Art Research on Diabetic Retinopathy)
Purpose: We have previously demonstrated that HspB4/αA-crystallin, a molecular chaperone, plays an important intrinsic neuroprotective role during diabetes, by its phosphorylation on residue 148. We also reported that HspB4/αA-crystallin is highly expressed by glial cells. There is a growing interest in the potential causative role of low-grade inflammation in diabetic retinopathy pathophysiology and retinal Müller glial cells’ (MGCs’) participation in the inflammatory response. MGCs indeed play a central role in retinal homeostasis via secreting various cytokines and other mediators. Hence, this study was carried out to delineate and understand the regulatory function of HspB4/αA-crystallin in the inflammatory response associated with metabolic stresses. Methods: Primary MGCs were isolated from knockout HspB4/αA-crystallin mice. These primary cells were then transfected with plasmids encoding either wild-type (WT), phosphomimetic (T148D), or non-phosphorylatable mutants (T148A) of HspB4/αA-crystallin. The cells were exposed to multiple metabolic stresses including serum starvation (SS) or high glucose with TNF-alpha (HG + T) before being further evaluated for the expression of inflammatory markers by qPCR. The total protein expression along with subcellular localization of NF-kB and the NLRP3 component was assessed by Western blot. Results: Elevated levels of IL-6, IL-1β, MCP-1, and IL-18 in SS were significantly diminished in MGCs overexpressing WT and further in T148D as compared to EV. The HG + T-induced increase in these inflammatory markers was also dampened by WT and even more significantly by T148D overexpression, whereas T148A was ineffective in either stress. Further analysis revealed that overexpression of WT or the T148D, also led to a significant reduction of Nlrp3, Asc, and caspase-1 transcript expression in serum-deprived MGCs and nearly abolished the NF-kB induction in HG + T diabetes-like stress. This mechanistic effect was further evaluated at the protein level and confirmed the stress-dependent regulation of NLRP3 and NF-kB by αA-crystallin. Conclusions: The data gathered in this study demonstrate the central regulatory role of HspB4/αA-crystallin and its modulation by phosphorylation on T148 in retinal MGCs. For the first time, this study demonstrates that HspB4/αA-crystallin can dampen the stress-induced expression of pro-inflammatory cytokines through the modulation of multiple key inflammatory pathways, therefore, suggesting its potential as a therapeutic target for the modulation of chronic neuroinflammation. View Full-Text
Keywords: αA-crystallin; Müller glial cells; NF-kB; metabolic stress; inflammatory markers αA-crystallin; Müller glial cells; NF-kB; metabolic stress; inflammatory markers
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MDPI and ACS Style

Nath, M.; Shan, Y.; Myers, A.M.; Fort, P.E. HspB4/αA-Crystallin Modulates Neuroinflammation in the Retina via the Stress-Specific Inflammatory Pathways. J. Clin. Med. 2021, 10, 2384. https://doi.org/10.3390/jcm10112384

AMA Style

Nath M, Shan Y, Myers AM, Fort PE. HspB4/αA-Crystallin Modulates Neuroinflammation in the Retina via the Stress-Specific Inflammatory Pathways. Journal of Clinical Medicine. 2021; 10(11):2384. https://doi.org/10.3390/jcm10112384

Chicago/Turabian Style

Nath, Madhu, Yang Shan, Angela M. Myers, and Patrice Elie Fort. 2021. "HspB4/αA-Crystallin Modulates Neuroinflammation in the Retina via the Stress-Specific Inflammatory Pathways" Journal of Clinical Medicine 10, no. 11: 2384. https://doi.org/10.3390/jcm10112384

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