Santacruzamate A Ameliorates AD-Like Pathology by Enhancing ER Stress Tolerance Through Regulating the Functions of KDELR and Mia40-ALR in vivo and in vitro

Abstract

Aggregated amyloid-β protein (Aβ) and Aβ-induced neuronal apoptosis have been implicated as critical factors in the pathophysiology of Alzheimer’s disease (AD). Certain preclinical results have indicated that the increased accumulation of protein aggregates in AD-affected neurons activates the unfolded protein response (UPR), a pathological phenomenon, which predominantly mediates the aberrant endoplasmic reticulum (ER) stress and apoptotic cascades in neuronal cells. In the present study, we confirmed that Santacruzamate A (STA, a natural product isolated from a Panamanian marine cyanobacterium) attenuates Aβ protein fragment 25–35 (Aβ 25–35 )-induced toxicity in PC12 cells and rescues cognitive deficits in APPswe/PS1dE9 mice by enhancing ER stress tolerance. We first demonstrated the anti-apoptotic effects of STA by evaluating caspase-3 activity, annexin V/propidium iodide (PI) staining, and terminal deoxynucleotidyl transferase dUTP nick end labeling staining. Behavioral testing of STA-treated APPswe/PS1dE9 mice showed that the pronounced memory impairments were ameliorated and that the consolidated memories were stably maintained over a 2-week period. The mechanistic studies provided evidence that STA inhibited Aβ 25–35 -induced UPR and ER stress by regulating the ER retention signal (KDEL) receptor, which reinforced the retention of resident chaperones in the ER lumen. Furthermore, STA regulated the expression of the mitochondrial intermembrane space assembly protein 40 (Mia40) and augmenter of liver regeneration (ALR), which ultimately attenuated the mitochondrial fission and apoptosis pathways. Together, our present findings suggest that the KDEL receptor and Mia40-ALR play a role in mitigating Aβ 25–35 -induced neurotoxicity, which might in turn positively regulate learning and memory. These observations support that STA may be a promising agent for reversing the progression of AD.

KDELR2 knockdown synergizes with temozolomide to induce glioma cell apoptosis through the CHOP and JNK/p38 pathways

“…The activation of PERK signaling has been shown to impair cell proliferation and promote apoptosis ( 45 ). Our results suggested that knockdown of KDELR2 significantly elevated the levels of phosphorylated PERK, which is consistent with the findings of a previous study ( 35 ). Activation of PERK results in subsequent phosphorylation of eIF2, causing signal switching to enhance apoptotic cell death by causing increased translation of ATF-4 ( 46 ), which promotes the expression of transcription factors including CHOP, a central factor in cell apoptosis ( 24 , 47 - 49 ).…”

“…As previously reported, KDELR knockdown attenuated the anti-apoptotic effects of Santacruzamate A in the pathophysiology of Alzheimer's disease (35), and KDELR2 knockdown reduced cell viability and inhibited colony formation in glioblastoma cells (30). To measure the effect of KDELR2 knockdown in glioma cells, we established KDELR2 knockdown U373 cells with siRNAs (siKDELR2#1, siKDELR2#2, and siKDELR2#3) evaluated them by RT-qPCR (Figure 2A) and western blot analysis (Figure 2B).…”

“…Whether ERS plays an important role in silencing KDELR2-induced glioma cell apoptosis remains uncertain. The KDELR-mediated retrieval of ER molecular chaperone proteins is limited by the expression of a mutant KDEL receptor, which dramatically aggravates ERS ( 35 , 41 ). It has been shown that KDELR2 interacts with GRP78 ( 26 ), and the expression of GRP78, which regulates the UPR in the ER, is upregulated when ERS occurs ( 25 ).…”

A Linarin Derivative Protects against Ischemia-Induced Neuronal Injury in Mice by Promoting Cerebral Blood Flow Recovery via KDELR-Dependent CSPG4 Activation

“…KDELR was originally demonstrated to be essential for the retrieval of ER-resident molecular chaperones, including a KDEL sequence from the ERGIC complex when the chaperones are released from the ER [ 40 , 41 ]. Nevertheless, it has been proven that KDELR activation mediates bidirectional transport between the ER and the Golgi complex and from the ERGIC to the cellular membrane and external secretion, which warrants the transportation of specific substrates to their suitable locations [ 42 , 43 ]. Consequently, the KDELR-mediated transport system is devoted to the dynamic equilibrium and functional control of many membranal and external proteins.…”

Marine Cyanobacteria: A Source of Lead Compounds and their Clinically-Relevant Molecular Targets

“…The combined chemotherapy led to the inhibition of HDAC1/2 as well as changes in HCC cell morphology, growth inhibition, cell cycle blockage and apoptosis in vitro and growth suppression of subcutaneous HCC xenograft tumors in vivo [56]. Santacruzamate A has also been explored as potential candidate lead compound for the treatment of endoplasmic reticulum (ER) stress-and unfolded protein response (UPR)-related neurodegenerative disorders, such as Alzheimer's disease [57].…”