Alzheimer's disease (AD) is a progressive disorder that starts with mild memory impairment and eventually results in a severe decline in cognitive function. Presently, two drug classes - cholinesterase inhibitors and N-methyl-d-aspartate (NMDA) receptor antagonists - offer temporary relief from AD symptoms [[1], [2], [3], [4], [5]]. On June 7, 2021, the Food and Drug Administration (FDA) granted accelerated approval to aducanumab (Aduhelm) for treating AD patients. This marked the first disease-modifying therapy approved by the FDA since 2003, attributed to its unique ability to selectively target pre-amyloid β (Aβ) seeds (spanning amino acids 3–7 of the Aβ peptide) to block Aβ aggregates [6,7]. Subsequently, on July 6, 2023, the FDA approved lecanemab, a humanized IgG1 monoclonal antibody that binds strongly to soluble Aβ aggregates, including oligomers and protofibrils [8]. The launch of these drugs reinforces our belief in the potential of therapies based on the amyloid deposition hypothesis. Although both drugs mitigate Aβ aggregation, their clinical efficiency remains limited in the use of addressing mild cognitive impairment (MCI) and mild dementia due to potential side effects, including amyloid-related imaging abnormalities of the effusion (ARIA-E) and hemorrhage (ARIA-H) [6,9]. Notably, both aducanumab and lecanemab are suitable only for patients who show amyloid presence through amyloid PET scans and are not recommended for those on anticoagulant treatments or carriers of apolipoprotein 4 (APOε4) [6,10]. This highlights the pressing need to innovate new therapeutic agents cater to diverse clinical requirements. The pathology of AD encompasses not just extracellular senile plaques formation from Aβ deposition but also intracellular neurofibrillary tangles (NFTs) due to hyperphosphorylation of tau protein, brain atrophy from neuronal death, and neuroinflammatory reaction [11]. Such multifaceted origins underscore the importance to develop multitarget drugs for comprehensive and effective therapy [[12], [13], [14], [15]].

MicroRNAs (miRNAs) are noncoding RNAs capable of modulating the expression of multiple proteins by specifically targeting genes associated with diseases, representing a strategy for RNA interference (RNAi). Several miRNAs play a role in AD's pathogenesis [16]. The downregulation of microRNA-195 (miR-195) is known to induce various pathological processes tied to AD, either directly or indirectly. This includes Aβ deposition through targeting the amyloid precursor protein (APP) and β-site APP cleaving enzyme 1 (BACE1) protein [[17], [18], [19]]. Additional processes related to AD and linked with miR-195 reduction include the hyperphosphorylation of tau protein through the activation of Cdk5/p25 and deactivation of protein phosphatase-2 A (PP2A) [20,21]. It also affects neuronal death and dendritic degeneration by elevating the death receptor-6 (DR6) protein [22], and triggers microglia polarization via the CX3CL1-CX3CR1 signaling pathway [23]. A recent study observed a decline in brain miR-195 levels correlating with the progression from normal aging to early-stage AD [19]. Moreover, in MCI patients, cerebrospinal fluid (CSF) miR-195 levels showed a positive correlation with cognitive performances as assessed by mini-mental status examination (MMSE), and an inverse relationship with CSF tau levels [19]. Additionally, miR-195 mitigates cerebral ischemia-reperfusion injury in rats by targeting the KLF5-mediated JNK signaling pathway [24]. These findings suggest that miR-195 could serve as a potential gene therapy for preventing and/or treating AD. Nonetheless, challenges like the instability of RNA-based therapeutics in circulation due to nucleases sensitivity, and their inability to cross the blood-brain barrier (BBB) and cell membrane owing to their large size and negative charge, hinder the broad adoption of miRNA-based therapies [25,26]. Consequently, crafting a drug delivery system that is stable, safe, affordable, cost-effective, and amenable to large-scale production is pivotal for the clinical transition of nucleic acid medications.

Liposomes are viewed as promising drug carriers given their biocompatibility, minimal toxicity and biodegradability [27]. Glycosylated liposomes can further enhance targeted brain delivery of encapsulated drugs to a certain degree [27,28]. The cationic cell-penetrating peptide (TAT), derived from the human immunodeficiency virus-1 transcription activator (HIV-1), boosts intracellular delivery of diverse cargoes due to its unique physicochemical properties [29]. If nanoliposomes are reasonably constructed, TAT peptide could aid glycosylated liposomes in penetrating the cerebral parenchyma. In this study, we developed nanoliposomes modified with P-aminophenyl-alpha-d-mannopyranoside (MAN) and TAT peptide. The extended PEG linker in MAN molecules allowed nanoliposomes to attach to the glucose transporter 1 (Glut1) on endothelial cells, facilitating initial interaction. Following this initial attachment, TAT peptides with a shorter PEG linker further enhanced the nanoliposomes ‘adherence to BBB, resulting in a dual uptake mechanism that involves both receptor-mediated endocytosis and adhesion-mediated pathways [30,31]. Dual modification with MAN and TAT peptides also influenced the nanoliposomes ‘distribution and metabolism. To enhance the loading efficiency of RNA, counteract premature release, prevent degradation by circulating nucleases, and facilitate lysosome escape, the cationic polymer polyethyleneimine (PEI) was employed to electrostatically bind negatively charged miR-195, forming polyelectrolyte complexes. This process culminated in the creation of enzymatically stable polyplexes composed of PEI and miR-195 complex [32] (Fig. 1). This research underscores that our optimized dual-ligand modified nanoliposomes, with a size of <200 nm, present a promising avenue for AD treatment.