The growth and osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs) play a crucial role in mitigating bone loss in individuals with osteoporosis. Wang et al (13) found that miR-100-5p is upregulated in hBMSCs from patients with osteoporosis, where it directly targets and suppresses transmembrane protein 135 expression. This suppression negatively regulates the proliferation and osteogenic differentiation of hBMSCs, thereby disrupting the bone formation process in osteoporosis (13). In a comparable study, Ai et al (14) noted an increase in miR-100-5p expression within the knee joint tissues of individuals with osteoporosis, indicating that miR-100-5p plays a role in the downregulation of lysine demethylase 6B (KDM6B) expression. This reduction in KDM6B's capacity to eliminate histone H3K27 (H3K27me3) methylation from the RUNX family transcription factor 2 (RUNX2) promoter led to diminished RUNX2 expression and hindered osteoblast differentiation, ultimately affecting the bone formation ability in these patients (14). Of note, several clinical studies have confirmed the potential diagnostic value of miR-100 for osteoporosis. The miR-100 expression levels were compared in 120 plasma samples taken from patients with osteoporosis and 120 samples taken from healthy controls using reverse transcription-quantitative PCR (RT-qPCR), in a study by Ding et al (15). The researchers found that the osteoporosis group had significantly higher levels of miR-100 expression. An area under the curve (AUC) of 0.8916 was determined by the receiver operating characteristic (ROC) curve analysis to indicate that miR-100 has diagnostic potential for osteoporosis (15). This result can be corroborated with the study by Chen et al (16), who also observed an upregulation of miR-100 expression in the serum of patients with osteoporosis and obtained a similar diagnostic efficacy (AUC=0.8875). These studies not only revealed the key regulatory role of miR-100-5p in the pathogenesis of osteoporosis, but also provided an important theoretical basis for the development of miRNA-based early diagnostic methods and targeted therapeutic strategies.

Wu et al (17) demonstrated that infrapatellar fat pad MSC-derived exosomes could deliver miR-100-5p into chondrocytes, reduce mTOR expression and promote autophagy activation, thereby inhibiting apoptosis and maintaining cartilage homeostasis to protect articular cartilage from damage and alleviate the condition of OA. Lai et al (18) used RT-qPCR to detect the expression level of miR-100-5p in the serum of 150 patients with knee OA (KOA) and 150 normal controls, and found that its expression was downregulated, with an AUC of 0.845, which suggests that miR-100-5p is closely related to KOA, and it also has a high diagnostic value.

Yang et al (19) identified an upregulation of miR-100-5p in exosomes derived from bone tissue of patients with NONFH. The research found that miR-100-5p inhibits osteogenic differentiation of hBMSCs and angiogenesis of human umbilical vein endothelial cells by inactivating the BMPR2/Smad1/5/9 signaling pathway. The results suggest that miR-100-5p could be a promising target for NONFH therapy (19).

In the acute phase after stroke, neuronal abnormalities are one of the key factors promoting the formation and expansion of infarct foci, whereas microglia activation plays an important role in the progression of neuroinflammation (20,21). The study by Xin et al (22) found that ischemia induced hyperactivation of M1 neurons, which in turn upregulated miR-100-5p expression in neurons and promoted its enrichment in extracellular vesicles (EVs). These miR-100-5p-carrying EVs can be taken up by neighboring microglia and neurons, and subsequently, miR-100-5p specifically binds to and activates the Toll-like receptor (TLR)7 through its U₁₈U₁₉G₂₀ motif, which in turn activates the NF-κB signaling pathway. This process not only leads to neuronal overexcitation and apoptosis but also exacerbates the neuroinflammatory response, ultimately exacerbating the pathology of ischemic brain injury (22). However, Cao et al (23) found that miR-100-5p can target to reduce the expression level of mTOR, activate autophagy response, inhibit apoptosis and thus alleviate the condition of cerebral infarction. This suggests a possible dual regulatory role for miR-100 in cerebral infarction.

It has been shown that MSC-derived exosomes (MSC-Exo) are effective in attenuating dopaminergic (DA) neuronal damage and reducing oxidative stress levels in PD models. The molecular mechanism is that miR-100-5p, delivered by MSCs-Exo, inhibits the expression of its target gene NADPH oxidase 4 (NOX4) and upregulates the expression levels of the antioxidant factors Keap-1, nuclear factor erythroid 2-related factor 2, heme oxygenase 1, superoxide dismutase (SOD)-1 and SOD-2, which reduces the accumulation of reactive oxygen species and attenuates the damage of DA neurons, and improves the motor deficit in PD (24). Loss of DA neurons caused by microglia activation is considered an important pathological factor in PD. Adipose-derived stem cells with small EVs reduce microglia activation by delivering miR-100-5p, targeting downregulation of deltex E3 ubiquitin ligase 3L expression, which in turn reduces the expression level of STAT1 and attenuates microglial cell activation, thereby decreasing the loss of DA neurons and ameliorating motor deficits (25).

It was found that the regulation of inflammation and microenvironment after SCI was beneficial to the recovery of neural tissues. miR-100 could attenuate the inflammatory response induced by microglia by inhibiting the activation of the NF-κB pathway by downregulating the expression level of TLR4. miR-100 also inhibited neuronal apoptosis by decreasing the expression of apoptosis-related proteins. These anti-inflammatory and anti-apoptotic effects together promoted the repair of neural tissues, which ultimately significantly improved motor function after SCI (26).

As key effector cells of allergic inflammation, eosinophils and the cytotoxic granule proteins they release have been shown to promote atherosclerotic plaque development (27). Gao et al (28) found that miR-100-5p in human umbilical cord MSC exosomes (hUCMSC-Exo) could target and downregulate frizzled class receptor (FZD)5, inhibit the Wnt/β-catenin pathway, significantly reduce the migration ability of eosinophils, promote apoptosis and reduce the release of eosinophil cationic protein and inflammatory factors, thus improving the atherosclerotic lesions in mice. Similarly, Ji et al (29) found that knockdown of circ-0004104 in vascular endothelial cells (VECs) with atherosclerosis-induced injury resulted in upregulation of miR-100 expression, which targeted and downregulated of TNF-α-induced protein 8 expression levels, and attenuation of VEC injury, thereby inhibiting the progression of atherosclerosis.

Zeng et al (30) observed upregulation of miR-100-5p expression in tissues of a rat model of cardiac hypertrophy induced by abdominal aortic constriction and in a model of cardiac hypertrophic cells generated by angiotensin II stimulation. Their molecular pathogenic mechanism is that miR-100-5p promotes the activation of autophagy by decreasing the expression of mTOR, leading to an increase in the surface area of cardiomyocytes, a decrease in cardiac function and the progression of cardiac hypertrophy (30).

Zhong et al (31) constructed a heart failure cell model by adriamycin induction. It was found that hUCMSC-EVs could inhibit oxidative stress and apoptosis by delivering miR-100-5p and targeting to reduce the expression level of NOX4, thus alleviating the condition of heart failure (31).

Liu et al (32) demonstrated that miR-100-5p expression was downregulated in EVs derived from macrophages in the rheumatoid arthritis microenvironment. Overexpression of miR-100-5p can target and reduce the expression level of mTOR, inhibit the proliferation of synovial cells and the exacerbation of inflammation and attenuate the disease progression of rheumatoid arthritis. Li et al (33) found that hUCMSC-sEVs deliver miR-100-5p, promote macrophage polarization toward an anti-inflammatory M2 phenotype and increase the proportion of regulatory T cells, thus playing an important role in the treatment of autoimmune dacryoadenitis.

The incidence of acute kidney injury (AKI) caused by ischemia/reperfusion (IR) injury has been increasing year by year. Chen et al (34) found that hUCMSC-sEVs could deliver miR-100-5p into HK-2 cells exposed to IR injury, which could inhibit apoptosis by decreasing the expression of FKBP5 and activating the AKT pathway. The hUCMSC-sEVs were injected intravenously into mice with IR injury and found to significantly inhibit apoptosis and protect the kidneys from damage. This provides a new approach for the treatment of AKI (34). Wu et al (35) found that miR-100-5p can treat atopic dermatitis. miR-100-5p exerts anti-inflammatory effects by downregulating the expression of forkhead box (FOX)O3, thereby inhibiting the activation of the downstream NLR family pyrin domain containing 3 signaling pathway. Zhang et al (36) demonstrated that miR-100 from hUCMSC-EVs promotes endometriosis development by inhibiting HS3ST2 expression and promoting endometrial stromal cell proliferation, invasion and migration. Furthermore, in the context of a high-fat diet, mice that overexpress miR-100 exhibited a reduction in weight gain, a decrease in both visceral and subcutaneous fat, lower levels of serum low-density lipoprotein cholesterol, as well as enhanced glucose tolerance and insulin sensitivity. The results indicate that miR-100 could provide protective advantages in the context of metabolic syndrome and hepatic steatosis induced by a high-fat diet (37).

Ge et al (38) showed that miR-100 downregulates C-X-C motif chemokine receptor 7 (CXCR7) expression in hepatocellular carcinoma (HCC) LM3 cells, which decreases proliferation, migration and invasion. The cancer stem cells of HCC showed a marked downregulation of miR-100 and miR-125, according to another study (58). In addition, the study demonstrated that stemness regulators, including SOX2, OCT4 and NANOG, reduced miR-100 and miR-125 expression, which in turn increased insulin-like growth factor (IGF)2 expression, activated the PI3K/AKT/mTOR pathway and preserved tumor stem cell characteristics (58). Vessels encapsulating tumor clusters (VETC) are a typical vascular architecture in HCC that allows complete tumor clusters to enter the bloodstream non-invasively. Elevated levels of angiopoietin 2 (Angpt2) in HCC cells are critical for the formation of VETCs. miR-100 targets and reduces mTOR expression, which in turn diminishes p70S6K phosphorylation, leading to a decrease in Angpt2 levels. This action inhibits VETC-dependent metastasis of HCC cells, preventing their migration into the bloodstream in a non-invasive manner (73). The ‘Warburg effect’ is a characteristic of cancer metabolism; it occurs when cancer cells generate energy primarily through glycolysis (74). Tumor cell metabolism and survival are greatly impacted by lactate dehydrogenase A (LDHA), an essential glycolysis enzyme. By focusing on and reducing LDHA expression, miR-100-5p blocks glycolysis in cancer cells when oxygen levels are low. This inhibits HCC cell proliferation and invasion by reducing lactate generation and glucose uptake (75). The results of these investigations provide credence to the idea that miR-100 can slow the development of HCC. Nevertheless, there is evidence that miR-100 may contribute to the aggressive development of HCC, according to certain research. Wang et al (62) found that MHCC-97H, a highly metastatic HCC cell line, which has high expression of β-galactoside α2,6 sialyltransferase I (ST6Gal-I), was better able to invade and migrate than its ST6Gal-I-knockdown counterpart. The stimulation of α-2,6 sialylation by ST6Gal-I was thought to be responsible for this action. It led to an increase in the activity of nerve sheath phospholipase-2 and caused miR-100-5p to be sorted into exosomes. When these exosomes were co-cultured with low-invasive HCC cells (HepG2), miR-100-5p was transferred into the HepG2 cells, resulting in reduced claudin 11 expression, increased PI3K expression and AKT phosphorylation. These changes led to the activation of the PI3K/AKT signaling pathway and enhanced the migratory and invasive potential of HCC cells (62).

Peng et al (12) demonstrated that BMPR2 expression could be enhanced by removing miR-100-3p, and that BMPR2 expression could be suppressed by increasing the levels of miR-100-3p. Subsequently, this inhibition slowed GC cell proliferation and set off cell death. Cao et al (39) found that miR-100 could target and reduce CXCR7 expression, which in turn suppressed GC-cell proliferation. The ability of lncRNAs to operate as competing endogenous RNAs allows for the regulation of miRNA activity (76). To inhibit miR-100-5p expression, Chen et al (11) found the lncRNA HAGLROS. After HAGLROS knockdown increased miR-100-5p and decreased mTOR expression, autophagy was improved and GC-cell proliferation and migration were suppressed (11). Evidence indicates, on the other hand, demonstrated that miR-100 expression is elevated in GC tissues and cells, and that levels show marked increases in relation to tumor aggressiveness. The transcription factor NME/NM23 nucleoside diphosphate kinase 2 (NME2) plays a critical role in miR-100 transcription. To achieve this, it acts with RNA polymerase II at its C-terminal domain, specifically targeting serine 5 for phosphorylation. This leads to an increase in miR-100 expression, which prevents GC cells from terminating their lives (59).

Through its direct targeting of CXCR7, miR-100 inhibits EC cell proliferation, migration and invasion (40). Additionally, circ-0006168 serves as an oncogenic circRNA, with its expression being markedly elevated in esophageal squamous cell carcinoma (ESCC) tissues and cell lines. Reducing circ-0006168 expression increased miR-100 expression and decreased mTOR expression, which suppressed ESCC cell motility, invasion and proliferation (56). Patients with ESCC have a poor prognosis due to lymphangiogenesis, which is a critical component of metastasis (77). There are multiple routes by which cancer-associated fibroblasts (CAF), an important part of the tumor microenvironment (TME), can promote tumorigenesis and progression (78). The study demonstrated that in ESCC, overexpression of IGF1R was caused by the deletion of miR-100-5p in CAF-derived exosomes. This overexpression activated the PI3K/AKT pathway, which in turn promoted the creation of lymphatic vessels and enhanced the metastasis of ESCC to lymph nodes. Based on these results, miR-100-5p may be able to target the lymphatic metastases of ESCC via exosome-mediated transport and suppress lymphangiogenesis (63).

Relative to non-metastatic CRC tissues, miR-100 expression is substantially higher in lymph node metastatic CRC tissues, according to various studies. By reducing the expression of targets such as mTOR, IGF1R, Fas and X-linked inhibitor of apoptosis, overexpression of miR-100-5p can prevent CRC metastasis (79). Furthermore, Jahangiri et al (70) discovered that miR-100, which was delivered via MSCs-Exo, reduced mTOR expression and indirectly increased miR-143. The expression of hexokinase 2 and KRAS was subsequently downregulated as a result of this, thereby inhibiting CRC cellular activities (70). Of note, Zhou et al (51) found that lncRNA PGM5-AS1 could target and inhibit miR-100-5p. The elevation of miR-100-5p expression and the subsequent downregulation of Smad4 promoted the proliferation, migration and invasion of CRC cells when PGM5-AS1 was knocked down (51).

Ottaviani et al (60) discovered that the SMAD2/3 signaling pathway is activated by TGF-β, leading to an increase in miR-100 transcription and the progression of PDA. However, miR-100-5p was found in significant levels in exosomes from hUCMSCs, according to Ding et al (71). Pancreatic cancer cells sped up the disease's development after absorbing these exosomes, which allowed miR-100-5p to enter the cells and stimulate cell proliferation and invasion.

Through downregulating FOXA1 expression, Xie et al (41) discovered that miR-100 impeded BC-cell proliferation, migration and invasion. In a similar study, Li et al (42) showed that miR-100-5p may reduce cell division cycle 25A expression, which in turn delayed BC cell migration, invasion and proliferation while speeding up apoptosis. The Wnt/β-catenin system is crucial in the genesis of cancer and regulates numerous key biological processes. It is also a highly conserved pathway. After being engaged, the Wnt pathway makes β-catenin more stable, which encourages it to go to the nucleus and take part in cellular activities (80,81). To enhance Wnt/β-catenin signaling, FZD8, a receptor for Wnt proteins, activates signaling pathways that are dependent on β-catenin, as well as those that are independent of it (82). According to Jiang et al (64), miR-100 suppresses the migration and invasion of BC cells by downregulating FZD8, which in turn reduces the expression of β-catenin, MMP-7, transcription factor 4 and lymphoid enhancer binding factor 1. Ultimately, this leads to inactivation of the Wnt/β-catenin pathway (64). Separately, Pakravan et al (72) transported miR-100 into BC cells using exosomes produced by MSCs. Once inside, miR-100 reduced mTOR expression, which in turn reduced hypoxia-inducible factor 1α expression, leading to less VEFG transcription and a reduction in BC cell proliferation, migration and invasion (72). Remarkably, a different study proposed that miR-100 could enhance the tumor-associated macrophage phenotype, which in turn promotes BC metastasis. Angiogenesis, tumor migration and anti-tumor immunity are all promoted by tumor-associated macrophages (TAM), an important part of the TME immune cell population. In BC, TAM express a high level of miR-100, which helps to preserve their phenotype by reducing the production of mTOR, an enzyme that promotes tumor growth. Furthermore, the Hedgehog pathway can be activated to improve the stemness and migration of BC cells, as miR-100-induced reductions in mTOR expression result in an increase in STAT5A-mediated IL-1R secretion (83).

Cancer cells may die when autophagy, a mechanism of cellular breakdown, is stimulated (84). There is a strong correlation between the amount of autophagosomes and the expression of light chain (LC)3; therefore, an increase in LC3 often correlates with an increase in autophagosome numbers. Beclin1 is involved in autophagosome formation during the early stages of autophagy (85,86). By reducing mTOR expression, Cai et al (87) demonstrated that miR-100-5p accelerates autophagy and promotes autophagosome formation. Endometrial cancer cells die and the disease advances more slowly as a result of this upregulation of Beclin1 and LC3 expression (87). By reducing SATB homeobox 1 expression, miR-100 suppressed cervical cancer cell proliferation, migration and invasion, as well as epithelial to mesenchymal transition (EMT) and the AKT/mTOR pathway, according to research by Huang et al (65). In OC, the lncRNA SDCBP2-AS1 was shown by Liu et al (52) to modulate miR-100-5p expression. Through inhibition of SDCBP2-AS1, miR-100-5p was upregulated, leading to the suppression of epithelial-derived protein 1 expression. This, in turn, enhanced migration, invasion and proliferation of OC cells while preventing their apoptosis (52).

Through its direct targeting and suppression of homeobox (HOX)A1 expression, He et al (43) showed that miR-100 suppresses the growth of NPC cells. A different team of researchers discovered that miR-100 can decrease IGF1R expression, which in turn decreases NPC cell motility and invasion (44). In RNA, the reversible methylation of the sixth position of adenine, called N6-methyladenosine (m6A), is dynamically regulated by methyltransferases and demethylases. The methyltransferases that play a role include methyltransferase 3, N6-adenosine-methyltransferase complex catalytic subunit (METTL3), METTL14, RNA binding motif protein 15B and zinc finger CCCH-type containing 13, with METTL3 serving as the primary catalytic enzyme. Research has demonstrated that m6A alteration modulates RNA function through controlling RNA expression, splicing, translocation, stabilization of lncRNAs and miRNA processing (88–91). Peng et al (53) discovered a variety of differentially expressed m6A-associated genes in NPC, including METTL3 and alkB homolog 5, RNA demethylase. The expression of METTL3 was observed to be markedly elevated in tumor tissues. METTL3 promotes the expression of the lncRNA ZFAS1 by decelerating RNA degradation processes and providing stability to the methylated ZFAS1 transcripts. The increased levels of ZFAS1 expression are significantly associated with unfavorable outcomes in NPC. The depletion of ZFAS1 led to an increase in miR-100-3p levels, which subsequently reduced autophagy-related 10 expression, stimulated the PI3K/AKT pathway and suppressed autophagy in tumor cells. The increased autophagy within the TME supplies tumor cells with additional energy, leading to the conclusion that the inhibition of autophagy by miR-100-3p diminishes the proliferation and migration of NPC cells (53,92). However, additional research indicates that miR-100-5p could also be involved in the advancement of NPC. The downregulation of FOXA1, a pioneer factor implicated in multiple tumors (93), resulted in heightened expression of miR-100-5p. This increase subsequently diminished RAS guanyl releasing protein 3 expression, thereby facilitating cell proliferation, migration and invasion in NPC (61).

Zhang et al (45) discovered that miR-100-5p has the capacity to suppress the proliferation of chordoma cells while enhancing apoptosis through the downregulation of IGF1R expression. Furthermore, it notably reduced the levels of N-calmodulin and waveform protein, while simultaneously enhancing the expression of E-calmodulin. This modulation effectively hinders the migration and invasion of chordoma cells by disrupting the EMT process (45). In a distinct investigation, Ma and Han (66) demonstrated that miR-100-5p has the capacity to inactivate the Wnt/β-catenin pathway through the suppression of FZD8 expression, subsequently leading to the inhibition of thyroid cancer cell proliferation and the induction of apoptosis.

The two main histological subtypes of lung cancer (LC) are small cell LC (SCLC) and non-SCLC (NSCLC), the former of which is more frequent. The development and progression of NSCLC are regulated by miR-100, according to multiple studies. Based on what we know about its upstream regulators, miR-100 is frequently downregulated in NSCLC. For instance, in NSCLC, brain metastasis is reduced when circ-0072309 is downregulated and miR-100 is upregulated. This, in turn, decreases atypical chemokine receptor 3 expression (57). A similar pattern was observed when the lncRNA HAGLROS was knocked down: miR-100 was upregulated, SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily A, member 5 was downregulated and NSCLC cell proliferation, migration, and invasion were all reduced (54). Furthermore, it has been demonstrated that miR-100 can lower HOXA1 expression, which in turn inhibits NSCLC cell proliferation, motility and invasion (46). Sevoflurane inhibited cell proliferation and migration by re-establishing miR-100-3p expression, which in turn decreased sterol O-acyltransferase 1 expression, as discovered by Fu et al (47), who noted that miR-100-3p was downregulated in A549 NSCLC cells.

The expression of miR-100 is negatively impacted by a number of cancers and is strongly linked to the advancement of tumors. By reducing the expression of NOX4, for instance, miR-100-5p blocks the proliferation, colony formation, migration and invasion of prostate cancer (PC) cells. This is achieved by targeting and suppressing the expression of mTOR (94). In renal cell carcinoma (RCC), Liu et al (95) discovered that miR-100 inhibits mTOR pathway expression, which in turn induces autophagy and downregulates NOX4 expression. As a result, the migration and invasion of RCC cells are suppressed (95). In mantle cell lymphoma, miR-100 inhibits cell growth via targeting mTOR (48). On the other hand, miR-100 is overexpressed and targets ATM in child acute myeloid leukemia, which promotes the proliferation of leukemia cells while preventing their death (49). In their study, Wei et al (50) discovered that miR-100-5p inhibits apoptosis and increases the survival and metastatic capacity of multiple myeloma cells by targeting and downregulating MTMR3 expression. Diffuse large B-cell lymphoma cells are unable to proliferate, migrate or invade when the lncRNA HAGLROS is silenced; this is because miR-100 is upregulated in this tumor type (55).