PP2A主要包含三個次單元分別為A(結構次單元)，B(調控次單元)，C(催化單元)。 調控次單元影響PP2A在細胞內存在的位置及PP2A受質的特異性。根據一些研究報告指出，Bβ 調控次單元基因與脊髓小腦運動失調症12型(spinocerebellar ataxia type 12，SCA12)有所關聯。 Bβ有兩種異構物，Bβ1及Bβ2，SCA12是由於Bβ1啟動子區域CAG三核苷酸擴充所致，目前尚未確定這個不被轉錄的三核苷酸擴充是影響Bβ1轉錄活性或涉及到Bβ1/Bβ2啟動子間使用頻率。在之前報導指出在PC12細胞中Bβ2-PP2A會進入粒線體中，並且促使該細胞進入細胞凋亡。 為了在動物模式中測試這個假設，我們建立神經組織粒線體過度表現Bβ2之轉殖基因小鼠。我們觀察到轉殖鼠有幾個異常的性狀，包含了體型小，毛髮稀疏，脊椎彎曲以及早期夭折等。 我們也利用量化的運動行為分析以及病理分析以了解這些基因轉殖鼠於粒線體中過度表現Bβ2之影響， 期許透過此結果能了解Bβ2於粒線體表現與SCA12之關聯。目前之研究結果顯示，因Bβ2於粒線體之表現的確提升了不同腦區PP2A之活性，也同時造成cytochrome c之釋出，MnSOD氧化壓力指標及Caspase 3細胞自戕分子之上升，而這些傷害進一步也的確讓我們看到小鼠在Rotarod及HomeCageScan行為上的異常，由這些結果看來，Bβ2於粒線體之表現的確造成神經退化。

Protein phosphatase 2A (PP2A) is a heterotrimeric serine/threonine phosphatase which consists of scaffolding (A), catalytic (C), and variable regulatory (B) subunits. The regulatory B subunits dictate subcellular localization and substrate specificity of the PP2A holoenzyme. The Bβ regulatory subunit gene was reported to be involved in spinocerebellar ataxia type 12 (SCA12). One of the Bβ splice variants, Bβ2, was postulated to target PP2A holoenzyme to mitochondria and promote apoptosis in an in vitro PC12 cell system. To test this hypothesis in vivo, we have established the transgenic mice with Bβ2 overexpression in the mitochondria of neuronal tissues. These transgenic mice show several phenotypical abnormalities, including smaller size, sparse hair, spinal curvature and early lethality. Quantitative motor activity and neuropathological analyses are also conducted to understand the neuronal effect caused by the Bβ2 overexpression in the mitochondria. Our results show that the mitochondria PP2A activity was increased by the Bβ2 overexpression. The cytochrome c releasing, oxidative stress index MnSOD, and apoptotic marker caspase 3 were all significantly up-regulated in the transgenic mice. Behavior performances characterized by Rotarod and HomeCageScan indicate an impairment in neuron function occurred in these animals. Taken together, we suggest that Bβ2 overexpression in the mitochondria of neuronal tissues could induce neuron degeneration.

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